Accepted Manuscript DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid T.S. Renuga Devi, J. Sharmi kumar, G.R. Ramkumaar PII: DOI: Reference:

S1386-1425(14)01312-2 http://dx.doi.org/10.1016/j.saa.2014.08.121 SAA 12642

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

28 May 2014 12 August 2014 24 August 2014

Please cite this article as: T.S. Renuga Devi, J. Sharmi kumar, G.R. Ramkumaar, DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.08.121

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DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid

T.S. Renuga Devi*a, J. Sharmi kumarb,d and G.R. Ramkumaarc a

Department of Physics, Women’s Christian College, College Road, Chennai – 600006, TN, India b

P.G. Department of Physics, Women’s Christian College, College Road, Chennai – 600006, TN, India c

Department of Physics, C. Kandaswami Naidu College for Men in Anna Nagar East, Chennai 600102, TN, India d

Research Scholar, Department of Physics, Periyar University, Salem – 636011. TN, India

*Corresponding Author (email: [email protected])

Abstract The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm-1 and 4000-50 cm-1 respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using Hartee-Fock and Density functional method (B3LYP) with the correlation consistent-polarized valence double zeta (cc-pVDZ) basis set and 6-311++G(d,p) basis set. The most stable conformer was optimized and the structural and vibrational parameters were determined based on this. The complete assignments were performed based on the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. With the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. Thermodynamic properties and Atomic 1

charges were calculated using both Hartee-Fock and density functional method using the ccpVDZ basis set and compared. The calculated HOMO-LUMO energy gap revealed that charge transfer occurs within the molecule. 1H and

13

C NMR chemical shifts of the molecule were

calculated using Gauge Including Atomic Orbital (GIAO) method and were compared with experimental results. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using Natural Bond Orbital (NBO) analysis. The First order Hyperpolarizability (β) and Molecular Electrostatic Potential (MEP) of the molecule was computed using DFT calculations. The electron density based local reactivity descriptor such as Fukui functions were calculated to explain the chemical reactivity site in the molecule. Key Words: CHES, FTIR, NMR, HOMO-LUMO, FUKUI FUNCTION

1. Introduction

2-(cyclohexylamino)ethanesulfonic acid (CHES) is an amphiphilic compound exhibiting a hydrophobic hydrocarbon moiety in the form of a cyclohexyl group and a hydrophilic part consisting of an amino group and a sulfonic acid group, making the molecule zwitterionic. CHES has detergent-like properties that make it capable of rupturing membrane structures, thereby releasing integral membrane proteins in a relatively mild way [1]. CHES is used as a buffer for studying pH-dependent processes in enzymology. The useful pH range of CHES is 8.6 – 10.0. 15mM of CHES adjusted to pH8.8 was found to provide a very efficient and stable electrophoretic system for the analysis of allopurinol and its metabolite oxypurinol [2]. Of the various solubilization procedures tried for liberation of diol dehydratase from membranes of C.glycolicum, sonication in CHES buffer released the diol dehydratase in a form that retained enzymic activity. The membrane suspension was almost entirely solubilized by sonication in 2

100mM CHES with pH 8.6 and 2 mM dithiothreitol [3]. Using Bovine Serum Albumin (BSA) as a model protein, it was demonstrated that CHES buffer and the fluorescent probe 2-(p-toluidino) naphthalene-6-sulfonic acid gave rise to the highest increase in fluorescence for BSA. Hence CHES buffer with pH range 10.2 was identified as the most suitable buffer to detect bovine whey proteins [4]. CHES buffer is used in the separation of chiral polychlorinated biphenyls by micellar electrokinetic chromatography using β and γ cyclodextrin mixtures [5]. Electrophoretic separation of bodipy-FI-labeled glycosphingolipids produced better results with CHES [6]. CHES is used as aggregation suppressor and found to be superior with respect to the final renaturation yield during the optimized procedure for renaturation of recombinant human bone morphogenetic protein-2 at high protein concentration [7]. Marked improvements in both purification rate and yield were observed using the zwitterionic buffer CHES in the quantitative study of continous flow-counterbalanced capillary electrophoresis [8]. 0.08M of CHES at pH 9 when used as separation buffer in the separation of a group of N-phenylpyrazole derivatives by micellar electrokinetic chromatography helped in determination of solute-micelle association constants [9]. CHES has been used to buffer the indirect detection of fast anions by capillary electrophoresis [10].

2. Experimental 2-(cyclohexylamino)ethanesulfonic acid with >99% purity was obtained from Sigma Aldrich, U.S.A. and was used without further treatments. FTIR spectrum of the powder sample was recorded in KBr in the range 4000 – 400 cm-1 using Perkin Elmer spectrometer with a resolution of ±1 cm-1. FT- Raman spectrum of the powder sample was recorded using 1064 nm line Nd:YAG laser as excitation wavelength in the region 4000-50 cm-1 using Bruker RFS 27

3

spectrometer with 8 scans at a resolution of 2 cm-1. The UV–Vis spectral measurements were recorded in the range 200 – 900 nm using a Varian Cary 5E-UV-NIR spectrophotometer. CHES is soluble in water at the concentration of 103.6 g/l at 20 °C.

1

H and

13

C Nuclear Magnetic

Resonance (NMR) spectral measurements were recorded with Bruker AVANCE III 500 MHz. The spectral measurements were carried out at Sophisticated Analytical Instrument Facility, IIT Madras, India.

3. Computational Details To provide complete information regarding the structural characteristics and the fundamental vibrational modes of CHES, the Restricted Hartree-Fock and DFT-B3LYP correlation functional calculations have been carried out. The calculations of geometrical parameters in the ground state were performed using Gaussian 09 programs [11], invoking gradient geometry optimization [12] on Intel core i4/2.93 GHz processor. The computations were performed at RHF/cc-pVDZ, B3LYP/cc-pVDZ and B3LYP/6-311++G(d,p) levels to obtain the optimized geometrical parameters, vibrational wavenumbers of the normal modes, IR intensity, atomic charges and thermodynamical parameters of the compound. The complete assignments were performed on the basis of the Potential Energy Distribution (PED) of the vibrational modes, calculated using Vibrational Energy Distribution Analysis (VEDA) 4 program. DFT calculations were performed using Becke’s three- parameter hybrid model using Lee-Yang-Parr (B3LYP) correlation functional method.

4

4. Results and Discussion

4.1 Molecular geometry The molecule CHES has 30 atoms with 84 normal modes of vibration. It belongs to the C1 point group symmetry. Fig. 1 shows the optimized geometry of the compound and Table 1 presents the optimized values obtained for bond lengths and bond angles. The various bond lengths and bond angles are found to be almost same at B3LYP/cc-pVDZ and B3LYP/6311++G(d,p) methods. The bond length between C1-C2 in RHF, B3LYP/cc-pVDZ and B3LYP/6-311++G(d,p) methods are found to be 1.525, 1.528 and 1.529 respectively which are in good agreement with the experimental value 1.53. The bond length between O13 and H30 in RHF, B3LYP/cc-pVDZ and B3LYP/6-311++G(d,p) are 0.953, 0.976 and 0.969 respectively. The B3LYP values are in good agreement with experimental value of 0.97. The bond angle between C6-C5-H20 in RHF and B3LYP methods are 109.2° which match exactly with the experimental value of 109.2°. The bond angle between C7-C8-C9 in RHF is 111.7° and in B3LYP methods gave the same value of 111.5°. The corresponding experimental value is 112°. The bond angle between C8-C7-H25 in RHF is 110.2° and in both B3LYP methods the value is 110.3°. The corresponding experimental value is 110.7°. The dihedral angle between C7-C8-C9H29 in RHF is -177.84°, in B3LYP/cc-pVDZ is -178.18°, in B3LYP/6-311++G(d,p) is -178.04° and the corresponding experimental value is -178.5°. The calculated geometric parameters can be used to determine the other parameters of CHES. The optimized bond lengths are larger than the experimental values as the theoretical calculations result from isolated molecules in gaseous state, where as the experimental results were from molecule in solid state [13]. Bond angles and dihedral angles were referred from [14-16]. 5

4.2 Vibrational analysis The observed and calculated frequencies using RHF/cc-pVDZ, B3LYP/cc-pVDZ and B3LYP/6-311++G(d,p) methods and their IR intensities and assignments are listed in Table 2. Experimental and Theoretical FTIR spectra of CHES are shown in Fig. 2. Experimental and Theoretical FT-Raman spectra of CHES are presented in Fig. 3. The description of the various band assignments are as follows.

4.2.1 CH2 Vibrations The six fundamentals associated to CH2 group are CH2 symmetric stretching, CH2 asymmetric stretching, CH2 scissoring, CH2 rocking, CH2 wagging and CH2 twisting. Here scissoring and rocking belong to in-plane vibration while wagging and twisting belong to outplane vibration. Socrates [17] has reported CH2 stretching modes in the region 2950-2860 cm-1. The asymmetrical stretching modes usually occur at higher wavenumbers than symmetrical stretching modes. Sajan et al [18] and Gunasekaran et al [19] have observed CH2 asymmetric stretching in the region 3000-2900 cm-1 and symmetric stretching in the region 2900-2800 cm-1. In the title molecule CH2 asymmetric stretching is observed at 3086 cm-1 in FTIR and at 3107 cm-1 in FT-Raman spectra with PED contribution of about 92% and 99% respectively. The B3LYP/cc-pVDZ values at which CH2 asymmetric stretching is calculated at 3138, 3080, 3065, 3062, 3060, 3059 cm-1 and the corresponding B3LYP/6-311++G(d,p) values are 3132, 3079, 3057, 3054, 3051, 3050 cm-1 , while RHF values are 3303, 3258, 3218, 3214, 3211 and 3210 cm-1. Band observed at 3023 cm-1 in FTIR and 3022 cm-1 in FT-Raman corresponds to CH2 symmetric stretching vibration with PED contribution 69%. The B3LYP/cc-pVDZ values which

6

corresponds to CH2 symmetric stretching are 3073, 3013, 3009, 3006 cm-1 and the corresponding B3LYP/6-311++G(d,p) values are 3067, 3010, 3005, 3003 cm-1 and the RHF values are 3231, 3166, 3164, 3160 cm-1. Generally the CH2 scissoring band in the spectra of hydrocarbons occur around 1468 cm-1 [20]. CH2 scissoring is observed at 1574, 1485, 1455, 1423 cm-1 in FTIR and at 1538, 1450, 1419 cm-1 in FT-Raman spectrum. The B3LYP/cc-pVDZ values which are attributed to CH2 scissoring are 1501, 1494, 1481, 1465, 1461, 1459, 1453, 1431 cm-1 and the corresponding B3LYP/6-311++G(d,p) values are 1521, 1508, 1502, 1495, 1489, 1484, 1454 cm-1 and RHF values are 1648, 1628, 1614, 1596, 1595, 1589, 1583, 1562 cm-1. Karabacak et al [21] have reported CH2 scissoring at 1466, 1457 cm-1 in FTIR and at 1475, 1456, 1442 cm-1 in FTRaman.

4.2.2 C-H, C-N and C-S vibrations The hetero aromatic structure shows the presence of C-H stretching vibration in the region 3100-3000 cm-1 which is the characteristic region for the ready identification of C-H stretching vibration [22]. C-H stretching is typically exhibited as a multiplicity of weak to moderate bands, compared with the aliphatic C-H stretching. In our present work 3023, 2923, 2902, 2859 cm-1 of FTIR and 3022, 2976, 2938, 2899, 2857 cm-1 of FT-Raman are assigned to C-H stretching. The B3LYP/cc-pVDZ values 3076, 3073, 3065, 3062, 3060, 3059, 3013, 3009, 3006, 3003, 2992, 2989 and 2976 cm-1 corresponds to C-H stretching vibration. The corresponding B3LYP/6-311++G(d,p) values are 3072, 3067, 3057, 3054, 3051, 3050, 3010, 3005, 3003,2998, 2990, 2987, 2985 cm-1 and the RHF values are 3236, 3231, 3218, 3214, 3211, 3210, 3166, 3164, 3158, 3147, 3142 cm-1. As indicated by PED, these modes involve maximum contribution of about 93% suggesting that they are due to pure stretching modes. Arivazhagan et

7

al [23] have also observed C-H stretching at 3000, 2983 cm-1 in FTIR and at 3083, 3000, 2995, 2983 cm-1 in FT-Raman spectra. Ramkumaar et al [24] have reported C-H stretching at 3167, 2933 cm-1 in FTIR and at 2941 cm-1 in FT-Raman spectra. The identification of C=N and C-N vibrations are a difficult task, as the mixing of several bands is possible in the region. Silverstein [25] has assigned C-N stretching in the region 13501000 cm-1 for amines. In our present work the bands at 1084, 955 cm-1 in FTIR are attributed to C-N stretching vibration. Calculated B3LYP/cc-pVDZ wavenumbers 1160, 1084 and 978 cm-1 corresponds to C-N stretching while the corresponding B3LYP/6-311++G(d,p) values are 1166, 1084 and 974 cm-1. The FTIR experimental value 1084 cm-1 is an exact match with both B3LYP values. The experimental and calculated wavenumbers are in good agreement. Turgay Polat et al [26] have reported C-N stretching vibrations at 1151, 1044, 896 cm-1 in FTIR and at 1158, 921 cm-1 in FT-Raman spectra. Renuga et al [27] have observed C-N stretching at 963 and 933 cm-1 in FTIR and at 935 cm-1 in FT-Raman spectra. Kanagathara et al [28] have reported C-N stretching vibrations at 1131, 1033 cm-1 in FTIR spectrum. The results obtained by literature are in good agreement with our present work. Colthup et al [29] and Socrates [17] have reported C-S stretching vibrations in the range 670 – 930 cm-1. C-S stretching vibrations are observed at 804, 775, 616 cm-1 in FTIR and at 806, 777, 612, and 405 cm-1 in FT-Raman spectra. The B3LYP/cc-pVDZ values for C-S stretching vibrations are 802, 775, 698, 412 cm-1 and the corresponding B3LYP/6-311++G(d,p) values are 795, 776, 689, 421 cm-1. Sarojini et al [30] have observed C-S vibration at 661 cm-1 in FTIR spectrum.

8

4.2.3. C-C and C-C-C vibrations The C-C aromatic stretching vibrations give rise to characteristic bands in the spectral range from 1600-1400 cm-1 [31]. C-C stretching vibrations for the title compound is observed at 1036, 1031, 903, 830, 790 cm-1 in FTIR and at 1037, 923 cm-1 in FT-Raman spectra. Theoretically C-C stretching vibration is observed at 1367, 1110, 1066, 1055, 1043, 933, 906, 857 and 815 cm-1 in B3LYP/cc-pVDZ method. While in B3LYP/6-311++G(d,p) it is observed at 1370, 1099, 1066, 1051, 1038, 931, 903, 851 and 809 cm-1. The corresponding RHF values are 1501, 1207, 1140, 1128, 1114, 998, 967, 934, 908 cm-1. The PED contributions are about 47%, 33% and 30%.

Santhana Krishnan et al [32] have observed C-C stretching vibrations at

wavenumbers 1059, 1007 cm-1 in FTIR and at 1053, 1012 cm-1 in FT-Raman spectra. Ramachandran et al [33] have observed C-C stretching vibrations at 1021, 1010, 822 cm-1 in FTIR and at 1020, 1013, 820 cm-1 in FT-Raman spectra. C-C-C bending vibrations are observed at 830, 569, 488 cm-1 in FTIR and at 562, 473 cm-1 in FT-Raman spectra. The corresponding B3LYP/cc-pVDZ values are 857, 577, 465, 448, 443 cm-1 and the B3LYP/6-311++G(d,p) values are 851, 580, 468, 458, 446 cm-1. 4.2.4. O-H and N-H vibrations The O-H group vibrations are likely to be the most sensitive to the environment, so they show pronounced shifts in the spectra of the hydrogen bonded species. The O-H stretching vibrations are usually observed in the region 3500 cm-1 [34]. O-H stretching is observed at 3777 cm-1 in FTIR spectrum. The corresponding B3LYP/cc-pVDZ, B3LYP/6-311++G(d,p) and RHF values are 3717, 3773 and 4074 cm-1 respectively. The PED contribution of about 100% 9

indicated that the mode is a pure O-H stretching vibration. Kanagathara et al [28] have also observed O-H stretching at 3882 cm-1 in FTIR spectrum. Santhana Krishnan et al [32] too have observed O-H vibration at 3660 cm-1 in FTIR. In all the hetero cyclic compounds the N-H stretching vibrations occur in the region 3500-3300 cm-1 [35-37]. The positions of the N-H stretching depends on the strength of hydrogen bond formed [38]. In primary amines, N-H stretching vibrations usually occur in the region 3500-3300 cm-1. Rofouei et al [39] have reported N-H stretching at 3301 cm-1 in FTIR. Arjunan et al [40] have reported 3430 cm-1 in FTIR and 3440 cm-1 in FT- Raman as N-H stretching. In our present investigation the wavenumber 3543 cm-1 in FTIR is assigned to N-H stretching. The corresponding B3LYP/cc-pVDZ, B3LYP/6-311++G(d,p) and RHF wavenumbers are 3463, 3495 and 3728 cm-1 respectively. The experimental value and B3LYP values are in good agreement. 4.2.5. SO2 and SO vibrations Symmetric SO2 stretching vibrations occur in the region 1125-1150 cm-1, while the asymmetric vibrations occur in the region 1295 -1330 cm-1 [41]. In the title molecule, SO2 symmetric stretching is assigned to 1098 cm-1 in FTIR, 1092, 1087 cm-1 in B3LYP/cc-pVDZ and 1095, 1087 cm-1 in B3LYP/6-311++G(d,p) and 1199, 1176 cm-1 in RHF method. Wavenumbers 1327, 1321 cm-1 in B3LYP/cc-pVDZ and 1338, 1333 cm-1 in B3LYP/6-311++G(d,p)

are

attributed to SO2 asymmetric stretching. Arivazhagan et al [42] have reported SO2 asymmetric and symmetric stretching vibrations at 1386 and 1112 cm-1 respectively in FTIR spectrum. Muthu et al [43] have observed SO2 asymmetric vibrations at 1286 cm-1 in FTIR and 1262 cm-1 10

in FT-Raman, while SO2 symmetric vibration at 1083, 1058 cm-1 in FTIR and at 1086, 1052 cm-1 in FT-Raman spectra. In our present investigation the wavenumbers 569, 538 cm-1 in FTIR are attributed to SO2 scissoring while 562, 520 cm-1 in FT-Raman corresponds to SO2 scissoring. The B3LYP/cc-pVDZ values 577, 527, 383 cm-1 and B3LYP/6-311++G(d,p) values 580, 535, 394 cm-1 corresponds to SO2 scissoring. SO2 twisting vibration is attributed to 317, 302, 159 cm-1 of B3LYP/cc-pVDZ, 324, 298, 151cm-1 of B3LYP/6-311++G(d,p) and 350, 335, 173 cm-1 of RHF. Muthu et al [43] have reported band at 478 cm-1 in FTIR and 313 cm-1 in FT-Raman as SO2 scissoring. 1154, 804, 756, 616 cm-1 of FTIR and 806, 612 cm-1 of FT-Raman corresponds to S-O stretching vibrations. The corresponding B3LYP/cc-pVDZ and B3LYP/6-311++ values are 1155, 802, 752, 698 cm-1 and 1149, 795, 734, 689 cm-1 respectively. The RHF values are 1258, 872, 822, 807 cm-1. 4.3 UV-Vis spectral analysis The time dependent density functional method (TD-DFT) is to detect exact absorption wavelengths at a relatively small computing time which correspond to vertical electronic transitions computed on the ground state geometry [44,45]. UV spectral studies are very useful in determining the transmittance and absorption of an optically active material [46]. Fig. 4 shows the UV spectrum of CHES and Table 3 shows the experimental and calculated absorption wavelength (λ), excitation state, oscillator strength (f), electronic absorption value and transition of CHES. According to Frank- Condon principle, the maximum absorption peak (λmax) corresponds to vertical excitation. Theoretical calculations predicts one intense electronic transition at 258.29nm with an oscillator strength f=0.018 and electronic absorption value 4.8003

11

eV, which is in good agreement with the experimental value 235 nm, corresponding to HOMO↔LUMO transition. The observed wavelength 235 nm corresponds to n-σ* transition. Another peak at 220.1nm with an oscillator strength 0.0094 and electronic absorption value 5.6331eV corresponds to the second excited state with transitions HOMO↔LUMO+1, HOMO↔LUMO+2 and HOMO↔LUMO+3. The third peak 207.18nm at 5.9843eV with oscillator strength 0.0031 corresponds to the third excited state and the corresponding transitions occur between HOMO↔LUMO+1 to HOMO↔LUMO+5. The maximum absorption wavelength corresponds to the electronic transition from HOMO ↔ LUMO with 98% contribution, followed by HOMO ↔ LUMO+1 with 91% contribution. 4.4 HOMO-LUMO Analysis The energy gap between the highest occupied and the lowest unoccupied molecular orbital is an important quantum chemical parameter that determines molecular electrical transport properties as it is a measure of electron conductivity. The HOMO energy characterizes the ability of electron to give and the LUMO energy characterizes the ability of electron to accept, and the gap between HOMO and LUMO characterizes the molecular chemical stability and explains the eventual charge transfer interactions taking place within the compound. This influences the biological activity of the molecule. When the energy gap is small, the compound will be easily excited. The HOMO energy is directly related to the ionization potential while, LUMO energy to electron affinity. HOMO energy and LUMO energy are theoretically calculated to be -5.8047eV and -0.2337eV. The energy gap is -5.571eV in B3LYP/cc-pVDZ method. In RHF method the HOMO energy is -9.6299eV and that of LUMO is 3.6300eV and the energy gap is found to be 12

13.2599eV. Fig. 5 represents the pictorial illustration of the frontier molecular orbitals and their respective positive and negative regions. In HOMO, negative site is over H16, C9, H26, C4 (partially), below H18 and between C6 and C5. Positive region is over H17, H22, C2 (partially), above H18 and between C4 and C5. HOMO is localized over the centre of the molecule. In LUMO, negative sites are found partially over H30, O13, O11, O12, C1 and C2. Positive site is partially over O11, O12, H30, O13, C1, H14, H16, H17, C2 and C4. The negative and positive sites indicate that LUMO is localized over the non-benzene region. 4.5 Mulliken population analysis Mulliken atomic charge analysis plays an important role in the application of theoretical calculation to molecular system, as atomic charges affect properties of molecular systems [47]. The electronic charge on an atom determines the bonding capability and molecular conformation. The atomic charge values were obtained by the Mulliken population analysis [48]. Mulliken population analysis was performed on the title molecule by B3LYP and RHF method using cc-pVDZ as the basis set and presented in Table 4. The oxygen atoms O11, O12 and O13 have charges -0.4197, -0.4317and -0.3123e respectively in B3LYP method. Of which O12 has the highest negative value. S10 has the maximum positive charge of 0.9384e and H30 has the next maximum charge of 0.1689e. Hence the oxygen atoms attract the sulphur atom S10 and the hydrogen atom H30. N3 atom has negative charge of -0.2357e and the H18 atom attached to it has positive charge 0.0716e in B3LYP method. Except C1, the other carbon atoms C2, C4, C5, C6, C7, C8 and C9 have positive atomic charges. Most of the hydrogen atoms exhibit negative charge in B3LYP method. The net charge of hydrogen atoms is 0.3832e in B3LYP. The presence of negative charge on nitrogen and oxygen atoms and net positive charge on hydrogen atoms may suggest the formation of intramolecular interaction in solid forms [49]. The advantage of 13

this population analysis is that it is useful for comparing changes in partial charge assignment between two different geometries with the same size basis set. The mulliken charges obtained by B3LYP/cc-pVDZ and RHF/cc-pVDZ methods are shown in Fig. 6.

4.6 Thermodynamic properties Using

B3LYP/cc-pVDZ,

B3LYP/6-311++G(d,p)

and

RHF/cc-pVDZ

several

thermodynamic properties like zero point energy, rotational constants, rotational temperatures, molar capacity, energy and entropy of CHES have been calculated and shown in Table 5. The statistical thermo chemical analysis of CHES was performed considering the molecule to be at room temperature 298.15K and one atmospheric pressure. All the thermodynamic data supply helpful information for further study of the title molecule. They can be used to compute the other thermo-dynamic energies according to relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamical field [50]. The difference in values calculated by both B3LYP and RHF methods are less. The zero point vibrational energy calculated by B3LYP methods is much lower than by the RHF method. The thermodynamic functions such as heat capacity at constant pressure (Cp), entropy (S) and enthalpy change (ddH) for the title compound were evaluated from the theoretical harmonic frequencies obtained from B3LYP/ cc-pVDZ method in the temperature range 100-1000 K and are listed in Table 6. From this table it is evident that the properties increase with the increase in temperature due to the fact that the vibrational intensities of molecules increase with temperature. The correlation between these thermodynamic properties and temperatures are fitted by quadratic formulae as follows and corresponding fitting factors (R2) for these

14

thermodynamic properties were found to be 0.9999, 0.9990 and 0.9996. The temperature dependent correlation graphs are shown in Fig. 7.   249.87677 0.91101  1.903110 

R2 = 0.9999

  13.76987 0.84436  3.1687910 

R2 = 0.9990

∆  8.06074 0.09222  2.5078910 

R2 = 0.9996

4.7 First order Hyperpolarizability The First order Hyperpolarizability (β) is a measure of induced dipole in a molecule in the presence of an electric field. The large value of hyperpolarizability is a measure of the nonlinear optical activity of the molecular system and is associated with the intermolecular charge transfer resulting from the electron cloud movement through Π conjugated frame work from electron donor to electron acceptor groups. Non-linear optical (NLO) responses induced in various materials are of great interest in recent years because of the potential applications in photonic technologies such as optical communication, computing data storage and image processing [51]. Recent efforts have been focused to develop organic molecules with large molecular non-linear optical response, improved optical transparency and good thermal stability [52]. The first order hyperpolarizability is a third rank tensor described by 3 X 3 X 3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to the Kleinman symmetry [53]. The components of β are defined as the coefficients in the Taylor series

15

expansion of the energy in the external electric field. The expression of the external Electric field when it becomes weak and homogeneous is        

1 1

2   6! "   "

E0 is the energy of the unperturbed molecules, Fα is the field at the orgin , µα, ααβ & βαβϒ are the components of dipole moment, polarizability and the first order hyperpolarizability respectively. The total static dipole moment µ, the mean polarizability α0, the anisotropy of the polarizability ∆α and mean first order hyperpolarizability β0 using the x,y and z components are defined as follows.   #$ % &'(/  

*++ ,-- ,.. / 0





 (/ ' ∆  2(/ #1$$  %% 2 1%%  && 2 3&&  $$ 4 6$$

!  3!$ !% !& 4(/ and !$  !$$$ !$%% !$&& !%  !%%% !$$% !%&& !&  !&&& !$$& !%%& Since the values of the polarizabilities (α) and hyperpolarizability (β) are reported in atomic units (a.u.), the calculated values were converted into electrostatic units (esu). [α: 1a.u. = 0.1482 X1024

esu; β: 1a.u. = 8.639 X 10-33 esu]. The first order hyperpolarizability(β) of the molecule along

16

with related properties were calculated using RHF/cc-pVDZ and B3LYP/cc-pVDZ methods are presented in Table 7. Urea is one of the molecules which has good non-linear optical property and it is has been used as a critical parameter for comparative studies. (µ = 1.3732 debye and β = 0.3728 X 10-30 esu). In RHF method, dipole moment (µ) is nearly 1.7 times greater than urea and the hyperpolarizability is 3.8 times greater than urea. In B3LYP method, the dipole moment is 1.7 times greater than urea and hyperpolarizability is 2.4 times greater than urea. Hence the title compound has good non-linear property. 4.8 NMR spectral analysis The experimental and theoretical chemical shift values of 1H and 13C NMR are given in Table 8. The experimental and theoretical NMR spectrum of 1H and 13C are shown in Fig. 8. Full geometry optimization of CHES was performed at the gradient corrected density functional level of theory using the hybrid B3LYP method based on Becke’s three parameters functional of DFT. Then, gauge- including atomic orbital (GIAO) 1H and

13

C chemical shift calculations of the

compound was made by the same method using cc-pVDZ as basis set. Aromatic carbons give signals in overlapped areas of the spectrum with chemical shift values of about 100 ppm [54]. In our present investigation the experimental chemical shift values of aromatic carbons are in the range 40.659 to 48.122 ppm. The nitrogen atom N3 have more electronegative property and polarizes the electron distribution in its bond to adjacent carbon atoms C2 and C4 and decreases the chemical shift values. The chemical shift value of C7 is smaller than the other aromatic carbons. The non-aromatic carbon atom C1 has the largest value of 57.013 ppm. The chemical shifts of hydrogen atoms obtained experimentally and theorectically are quite low. The hydrogen atoms attached to nearby electron- withdrawing atom or group can decrease the

17

shielding and move the resonance of attached proton towards a higher frequency, whereas electron- donating atom or group increases the shielding and moves the resonance towards a lower frequency [55]. The chemical shift values of hydrogen atoms obtained by B3LYP method ranges from 0.318 to 5.477 ppm and the experimental chemical shift values ranges from 1.243 to 4.601 ppm. 4.9 Natural Bond Orbital Analysis Natural Bond Analysis (NBO) stresses the role of intermolecular orbital interaction in the complex, particularly charge transfer. This is carried out by considering all possible interactions between filled donor and empty acceptor natural bond orbital and estimating their energetic importance by second order perturbation theory. The NBO analysis of CHES has provided detailed insight into the nature of electronic conjugation between the bonds in this molecule. Natural bond analysis is a measure of delocalization or hyperconjugation. The hyperconjugation interaction energy was deduced from the second order perturbation approach [56].



34

 ∆56

38, :4  75 ∈ :∈ 8

Where qi is the donor orbital occupancy, Єi and Єj are diagonal elements and F (i,j) is the off diagonal NBO Fock matrix element. The larger the E(2) value, the more intensive is the interaction between electron donors and electron acceptors. The more the donating tendency of electron donors to electron acceptors, then greater will be the extent of conjugation of the whole system [57]. The interaction between lone pair LP (3) of type O11 with σ* (S10 – O13) results in a stabilization energy of 38.23 KJ/mol and lone pair LP (3) of type O12 with σ* (S10 – O13) 18

results in stabilization energy of 39.58 KJ/mol. These indicate larger delocalization. The intramolecular hypeconjugative interaction of σ (S10 – O13) to σ* (S10 - O11) leading to strong stabilization of 6 KJ/mol. The intramolecular hyperconjugative interaction of σ (C1 – S10) to σ* (S10 - O13) and σ (C4 – H19) to σ* (N3 – H18) leads to stabilization of 4.91 and 4.41 KJ/mol respectively. These interactions are observed as increase in electron density in antibonding orbital that weakens the respective bonds. These charge transfer interactions in CHES are responsible for biological properties. Hence CHES structure is stabilized by these orbitals interactions. In CHES, the oxygen has larger percentage of NBO and gives the larger polarization co-efficient because it has the higher electronegativity. The calculated values of E(2) are given in Table 9. 4.10 Natural Population Analysis The Natural Population Analysis (NPA) is an alternative method to the conventional Mulliken Population Analysis (MPA). It exhibits an improved numerical stability and describes the electron distribution in compounds of high ionic character in a better way. NPA are found to give a satisfactory description of the molecules, providing a unified treatment of covalent and extreme ionic limits at modest computational cost. The calculated natural atomic charge values from the natural population analysis and mulliken population analysis procedures using B3LYP/cc-pVDZ are listed in Table 10. The NPA from the natural bonding orbital method is better than MPA scheme. The table compares the atomic charge site of CHES of both methods. All carbon atoms carry negative charge. From NPA it is observed that the nitrogen atom N3 possesses negative charge of -0.7557. The oxygen atoms O11, O12 and O13 have negative charges -0.8983, -0.9230 and -0.8889 respectively. O12 has the maximum negative charge. S10 has positive charge of 2.3187, which is the highest. It may be due to the negative charge of 19

oxygen atoms. All the hydrogen atoms possess positive charge. H30 and H18 have the highest contribution of 0.4964 and 0.3863 among the hydrogen atoms, which may be due to the presence of O13 and N3 respectively. 4.11 Molecular Electrostatic Potential The electrostatic potential V(r) that is created in the space around a molecule by its nuclei and electrons (treated as static distributions of charge) is a very useful property for analyzing and predicting molecular reactive behavior. The electrostatic potential is a powerful tool which provides insights into intermolecular association and molecular properties of small molecules, actions of drug molecules and their analogs [58], the biological function of hemoglobin and enzyme catalysis. Electrostatic potential maps illustrate the charge distribution of molecules three dimensionally. The maps enable us to visualize the charge distributions of molecules and charge related properties of molecules [59]. Negative electrostatic potential corresponds to attraction of the proton by the concentrated electron density in the molecules (from lone pairs, pibond etc). Positive electrostatic potential corresponds to repulsion of the proton by the atomic nuclei in regions where low electron density exists and the nuclear charge is incompletely shielded. The Molecular Electrostatic Potential (MEP) at a point r in the space around a molecule (in a.u.) can be expressed as >→A→

B

C1D ′ →2ED D′→D



where ZA is the charge on nucleus A, located at RA and ρ(r’) is the electronic density function of the molecule. The first and second terms represent the contributions to the potential due to nuclei

20

and electrons respectively. V(r) is the resultant at each point r, which is the net electrostatic effect produced at the point r by both the electrons and nuclei of the molecule. MEP is related to electron density and is a powerful tool in determining sites for electrophilic attack, nucleophilic attack and hydrogen – bonding interaction [60].The total electron density and MESP surfaces of the molecule under investigation are constructed by using B3LYP/cc-pVDZ method. The figures illustrate an electrostatic potential model of the compound, computed at the 0.002 a.u. isodensity surface. Fig. 9(A) represents the counter map of the molecular electrostatic potential surface of CHES and Fig. 9(B) the molecular electrostatic potential surface of CHES. Total electron density of CHES is shown in Fig 10. The different values of the electrostatic potential at the surface are represented by different colours. Potential increases in the order red ˂ orange ˂yellow ˂green ˂ blue. Electrophilic regions are represented by red, nucleophilic by blue and green indicates neutral electrostatic potential. The atoms O11, O12, O13 and S10 were electrophilic sites. Nitrogen atom N3 was a nucleophilic site. From these results, one can say that the nitrogen atom and hydrogen atoms indicate strongest attraction, while oxygen atoms and sulphur atom indicate strongest repulsion. These sites give information about the region from where the compound can have intermolecular interactions. The figures confirm the different positive and negative sites of the molecule in accordance with the total electron density surface. 4.12 Chemical reactivity Global reactivity descriptors Conceptual density functional theory based global reactivity descriptors are used to understand the relationship between structures, stability and global chemical reactivity. These 21

descriptors are employed in the development of quantitative structure activity (QSAR), structure property (QSPR) and structure toxicity (QSTR) relationships [61]. QSAR methodology is one of the most powerful tools for describing the relationships between biological activity and the physicochemical characteristics of molecules. The global descriptor of hardness has been an indicator of overall stability of the system. According to the Koopman’s theorem [62] associated within the framework of HF self-consistent field molecular orbital theory the ionization energy and electron affinity can be expressed through HOMO and LUMO orbital energies. F  GHIH and

J  KLIH

The higher HOMO energy corresponds to the more reactive molecule in the reactions with electrophiles, while lower LUMO energy is essential for molecular reactions with nucleophiles [63]. Knowing the HOMO-LUMO energy gap, the nature of the molecule (hard or soft) can be determined. The molecule having a large energy gap are known as hard molecules [64] and those with less energy gap are known as soft molecules. The soft molecules are more polarizable than the hard ones as they require less energy for excitation. The hardness of the molecule is determined by the formula 1 M  3F  J4 2 (

M  3 KLIH  GHIH 4 

and global softness inverse of global hardness is obtained by the formula 

1 2M

22

The electron affinity can also be used in combination with ionization energy to give electronic chemical potential (µ) defined by Parr and Pearson [65] as the characteristic of electronegativity of molecules. 1    3F J4 2 1   3KLIH GHIH 4 2   χ 1 2

χ   3KLIH GHIH 4 The global electrophilicity index (ω) was introduced by Parr [66] and calculated using the electronic potential µ and chemical hardness η

N

  2M

According to this definition, index measures the propensity of a species to accept electrons. A good, more reactive, nucleophile is characterized by a lower value of µ, ω and conversely a good electrophile is characterized by a high value of µ and ω. Table 11 presents the values of electronegativity (χ), chemical potential (µ), global hardness (η), global softness (S) and global electrophilicity index (ω). Local reactivity descriptors Fukui function is one of the widely used local density functional descriptors to model chemical reactivity and site selectivity. The atom with the highest fukui function is highly 23

reactive compared to the other atoms in the molecule. Fukui functions have been calculated for large number of organic molecules, and are found to be always positive. Numeric and algebraic considerations allowed the identification of several boundary conditions for negative values for fukui functions. Negative fukui functions are found to be unlikely, except when very short interatomic distances are present. Fukui function predicts favourable interactions between molecules that are far apart. The fukui function [67] denoted by f(r) is defined as the differential change in electron density due to an infinitesimal change in the number of electrons O3=4   P

QC3D4 QR

S

T3D4

(1)

Where ρ(r) is the electron density, U  B V3=4W= is the total number of electron in the system and v(r) is the external potential acting on an electron. A molecule is susceptible to nucleophilic attack at sites where f+ (r) is large. Similarly, a molecule is susceptible to electrophilic attack at sites where f(r) is large, because these are the regions where electron removal leads to least destabilization. In density functional theory, the fukui functions are the selectivity indicators for electron – transfer controlled reactions. The electron density based local reactivity descriptors namely local hardnessη, local softness S, and the fukui function (f) are proposed to explain the chemical selectivity or reactivity at a particular site of a chemical system. It has also been shown that local hardness is a reliable intermolecular reactivity descriptor [68] and local softness and fukui function are more reliable intramolecular site selectivity descriptors [69]. Yang and Mortier [70] have given a simple procedure to calculate the atomic condensed fukui function indices based on mulliken population analysis are OX,  # 73U 14  73U4 '

for nucleophilic attack

24

OX  # 73U4  73U  14'

for electrophilic attack

OX  # 73U 14  73U  14'

for radical attack

where N, N-1 and N+1 are total electrons present in neutral, cation and anion state of molecule respectively. OX , OX, describe the ability of an atom to accommodate an extra electron or to cope with the loss of an electron and

OX is considered as an indicator for radical

reactivity. 7X is the atomic charge at the kth site. In addition to these functions, local softness ( YX, ,YX ,YX ) and local electrophilicity indices (NX, , NX , NX ) are also used to describe the reactivity of atoms in molecule. Values of fukui function, local softness and local electrophilicity indices of atoms of the molecule CHES are given in Table 12. It has been found that MPA schemes predict S10 has higher OX value indicating it as a possible site for electrophilic attack. The other sites for electrophilic attack were H14, O11 and H16. The observation of the reactive sites by YX, was found almost identical to OX . From the table, the highest nucleophilic attack site was found to be N3 and the other sites were H16, H17 and H18. The radical attack was predicted at N3, H16, O11, and H17. Of all the attacks, it was observed that nucleophilic was the biggest reactivity site compared to the electrophilic and radical attack. 5. Conclusion The molecular geometry of the molecule in the ground state has been calculated by using RHF/cc-pVDZ and DFT (B3LYP) methods with cc-pVDZ and 6-311++G(d,p) basis set. Several thermodynamical parameters were obtained and analyzed with RHF and DFT methods using the same basis set. UV spectral analysis of the molecule was also carried out. The HOMO-LUMO

25

energy gap helped in analyzing the chemical reactivity of the molecule. Atomic charges of the molecule were studied by both the RHF and DFT methods. The 1H and

13

C NMR chemical

shifts were calculated and compared with the experimental results. The calculated dipole moment and first order hyperpolarizability results indicate that the molecule has a reasonably good nonlinear optical behavior. The NBO analysis indicated the intramolecular charge transfer between the bonding and antibonding orbitals. Fukui functions, local softness and electrophilicity were calculated. MESP confirmed the different negative and positive potential sites of the molecule in accordance with the total electron density surface. On comparing the experimental results with the theoretically predicted values, it was found that the B3LYP method was more accurate, proving that DFT is a reliable method for molecular vibrational analysis. References [1] M.J. Taylor, Y.Pignat, Cryobiology, 19 (1982) 99-109 [2] Tomas Perez-Ruiz, Carmen Martinez-Lozano, Virginia Tomas, Raquel Galera, Journal of Chromatography B 792 (2) (2003) 303-308. [3] M.G. Hartmanis, T.C, Stadtman, Proc. Natl. Acad. Sci. USA, 84(1) (1987) 76-79. [4] I. Benito, M.L Marina, J.M. Saz, J.C. Diez-Masa, Journal of Chromatography A, 841(1) (1999) 105-114 [5] M.L. Marina, I. Benito, J.C. Diez-Masa, M.J. Gonzalez, Journal of Chromatography A, 752 (1996) 265-270. [6] S.A. Sarver, R.B. Keithley, D.C. Essaka, H.Tanaka, Y.Yoshimura, M.M. Palcic, 26

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[37] N. Puviarasan, V. Arjunan, S. Mohan, Turkey, J. Chem. 26 (2002) 323 -334. [38] H. Ringertz, Acta Crystallogr. B27 (1971) 285-291. [39] M.K. Rofouei, N. Sohrabi, M. Shamsipur, E. Fereyduni, S. Ayyappan, N. Sundaraganesan, Spectrochimica Acta Part A, 76 (2010) 182-190. [40] V. Arjunan, Arushma Raj, P. Raaaavindran, S. Mohan, Spectrochimica Acta Part A, 118 (2014) 951-965. [41] N.P.G. Roeges, “A Guide to the Complete Interpretation of Infrared Spectra of Organic Structures”, Wiley, New York, 1994. [42] M.Arivazhagan, S.Prabhakaran, R.Gayathri, Spectrochimica Acta Part A, 82 (2011) 332339. [43] S. Muthu, J.Uma Maheswari, Tom Sundius, Spectrochimica Acta Part A, 108 (2013) 307-318. [44] D. Jacquemin, J.Preat, E.A. perpete, Chem. Phys. Lett. 40 (2005) 254-259. [45] M.Cossi, V. Barone, J.Chem. Phys. 115 (2001) 4708-4717. [46] C.N.R. Rao, “Ultraviolet and Visible Spectroscopy Chemical applications”, plenum Press, New York, 1975. [47] V.K. Rastogi, M.A. Palatox, L.Mittal, N.Peica, W.Kiefer, K.Lang, P.Ohja, J. Raman

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[59] C. Munoz-Caro, A.Nino, M.L. Sement, J.M. Leal, S. Ibeas, J. Org. Chem. 65 (2000) 405410. [60] F.J. Luque, J.M. Lopez, M. Orozco, Theor. Chem. Aca. 103 (2000) 343-345. [61] R. Vijayaraj, V. Subramanian, P.K. Chattaraj, J. Chem. Theo. Comput. 5(10) (2009) 27442753. [62] T. Koopmans, Physica 1 (1933) 104-113. [63] A. Rauk, “Orbital Interaction Theory of Organic Chemistry”, 2nd Ed., John Wiley & Sons, New York, 2001. [64] R.G. Pearson, J. Am. Chem. Soc. 107 (1985) 6801-6806. [65] R.G. Parr, R.G. Pearson, J. Am. Chem Soc. 105, (1983) 7512-7516. [66] R.G. Parr, L.Szentpaly, S.Liu, J. Am. Chem, Soc. 121 (1999) 1922-1924. [67] R.G. Parr, W. Yang, J. Am. Chem. Soc. 106 (1984) 4049-4050. [68] W. Langenaekar, F De Proft, P Greerlings, J. Phys. Chem. 99 (1995) 6424-6431. [69] S. Krishnamurthi, R.K. Roy, R. Vetrivel, S. Iwata, S. Pal, J. Phys. Chem. 101 (1997) 72537257. [70] W.Yang, J. Mortier, J. Am. Chem. Soc., 108 (1986) 5708-5711.

32

Figures CHES

Fig 1.Optimized molecular structure and atomic numbering of 2-(cyclohexylamino)ethanesulfonic acid

1

Fig 2. Experimental and Theoretical FTIR spectra of 2-(cyclohexylamino)ethanesulfonic acid

2

Fig 3. Experimental and Theoretical FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid

3

Fig 4. UV spectrum of CHES, Soluble in water (103.6 g/l) at 20 °C

4

LUMO (First excited state)

HOMO (Ground state)

Fig 5. The atomic orbital composition of the frontier molecular orbital for CHES

5

B3LYP/cc-pVDZ RHF/cc-pVDZ

1.4 1.2 1.0 0.8

Charge

0.6 0.4 0.2 0.0 C1 C2 N3 C4 C5 C6 C7 C8 C9 S10O11O12O13H14H15H16H17H18H19H20H21H22H23H24H25H26H27H28H29H30

-0.2

Atoms

-0.4 -0.6

Fig 6. Plot of Mulliken charges obtained by B3LYP/cc-pVDZ and RHF/cc-pVDZ methods.

6

Enthalpy, ddH (kj/mol)

350 300 250 200 150 100 50 0

Heat Capacity, Cp (j/mol.k)

600 500 400 300 200 100

Entropy, S (j/mol.k)

1000 900 800 700 600 500 400 300 0

200

400

600

800

1000

Temperature (K)

Fig 7. Correlation graph between Entropy, Heat Capacity and Enthalpy with Temperature

7

Fig 8. NMR Spectrum of CHES

8

Fig. 9(A) The counter map of the molecular electrostatic potential surface of CHES (B) The molecular electrostatic potential surface of CHES

Fig 10. Total electron density of CHES

9

TABLES CHES

Table 1: Experimental values and theoretically optimized geometrical parameters of CHES obtained by B3LYP/6-311++G(d,p), B3LYP/cc-pVDZ and RHF/cc-pVDZ methods. RHF/ ccpvdz

B3LYP/

RHF/

B3LYP/

cc-pvdz

cc-pvdz

B3LYP/ 6311++G(d,p)

C1-C2

1.525

1.528

1.529

1.53

S10-C1-C2-N3

-177.33

-173.61

-177.35

C1-S10

1.772

1.81

1.804

1.81

S10-C1-C2-H16

57.50

60.16

57.30

C1-H14

1.089

1.1

1.091

1.09

S10-C1-C2-H17

-59.12

-55.83

-59.71

C1-H15

1.09

1.101

C2-N3

1.447

1.458

1.092

1.09

H14-C1-C2-N3

-59.29

-55.89

-59.61

1.46

1.47

H14-C1-C2-H16

175.55

177.89

175.05

C2-H16

1.095

1.108

1.098

1.09

H14-C1-C2-H17

58.92

61.89

58.04

C2-H17

1.09

1.102

1.093

1.09

H15-C1-C2-N3

62.40

66.76

62.77

N3-C4

1.458

1.469

1.471

1.47

H15-C1-C2-H16

-62.76

-59.46

-62.58

N3-H18

1.006

1.023

1.017

1.01

H15-C1-C2-H17

-179.38

-175.46

-179.58

C4-C5

1.53

1.536

1.535

1.53

C2-C1-S10-O11

178.58

179.60

178.24

C4-C9

1.536

1.543

1.543

1.53

C2-C1-S10-O12

43.96

43.65

43.35

C4-H19

1.096

1.107

1.099

1.09

C2-C1-S10-O13

-67.87

-67.60

-68.61

C5-C6

1.53

1.535

1.536

1.53

H14-C1-S10-O11

57.02

58.16

56.63

C5-H20

1.097

1.108

1.099

1.09

H14-C1-S10-O12

-77.61

-77.79

-78.27

C5-H21

1.091

1.102

1.093

1.09

H14-C1-S10-O13

170.56

170.95

169.77

C6-C7

1.529

1.535

1.535

1.53

H15-C1-S10-O11

-57.08

-56.14

-57.67

C6-H22

1.093

1.103

1.095

1.09

H15-C1-S10-O12

168.30

167.91

167.43

C6-H23

1.096

1.106

1.098

1.09

H15-C1-S10-O13

56.47

56.65

55.47

C7-C8

1.529

1.534

1.534

1.53

C1-C2-N3-C4

163.20

165.77

164.16

C7-H24

1.096

1.107

1.098

1.09

C1-C2-N3-H18

-71.66

-70.63

-70.79

C7-H25

1.093

1.103

1.095

1.09

H16-C2-N3-C4

-74.49

-71.54

-73.38

C8-C9

1.531

1.536

1.537

1.53

H16-C2-N3-H18

50.66

52.06

51.66

C8-H26

1.093

1.103

1.095

1.09

H17-C2-N3-C4

45.17

48.02

46.11

C8-H27

1.096

1.106

1.098

1.09

H17-C2-N3-H18

170.31

171.62

171.16

C9-H28

1.098

1.108

1.099

1.09

C2-N3-C4-C5

-171.01

-170.60

-172.39

C9-H29

1.093

1.103

1.095

1.09

C2-N3-C4-C9

64.42

64.71

62.94

S10-O11

1.434

1.47

1.451

1.42

C2-N3-C4-H19

-55.10

-54.66

-56.40

S10-O12

1.443

1.481

1.46

1.42

H18-N3-C4-C5

63.60

65.43

62.16

S10-O13

1.607

1.675

1.657

1.52

H18-N3-C4-C9

-60.97

-59.26

-62.51

O13-H30

0.953

0.976

0.969

0.97

H18-N3-C4-H19

179.50

-178.63

178.15

N3-C4-C5-C6

178.79

178.32

178.64

Structural parameters

cc-pvdz

B3LYP/ 6311++G(d,p)

Experimental

Bond length

Structural parameters

Experimental

Dihedral angle(°)

Bond angle (°) C2-C1-S10

114

113.3

114

N3-C4-C5-H20

-60.23

-60.91

-60.50

C2-C1-H14

111

111.2

111.3

C3-C4-C5-H21

55.62

54.70

55.44

-176.4

C2-C1-H15

112.9

113.3

112.8

C9-C4-C5-C6

-54.21

-54.34

-54.24

C1-C2-N3

108.7

108.9

108.5

C9-C4-C5-H20

66.77

66.43

66.63

C1-C2-H16

109.4

109

109.5

109.5

C9-C4-C5-H21

-177.38

-177.97

-177.44

C1-C2-H17

108.5

108.4

108.9

109.4

H19-C4-C5-C6

63.76

63.54

63.79

S10-C1-H14

104.8

104.7

104.4

H19-C4-C5-H20

-175.26

-175.70

-175.34

S10-C1-H15

105.5

105

105.2

H19-C4-C5-H21

-59.41

-60.09

-59.41

C1-S10-O11

108.8

108.9

109

N3-C4-C9-C8

177.90

178.34

178.38

C1-S10-O12

110.7

110.4

110.9

N3-C4-C9-H28

56.93

57.56

57.57

C1-S10-H13

100.5

99

98.7

N3-C4-C9-H29

-59.61

-58.75

-58.96

H14-C1-H15

108.2

108.6

108.6

109.4

C5-C4-C9-C8

54.22

54.40

54.48

N3-C2-H16

114.1

115

114.3

116.6

C5-C4-C9-H28

-66.75

-66.38

-66.33

N3-C2-H17

108.8

108.4

108.3

C5-C4-C9-H29

176.72

177.30

177.14

C2-N3-C4

116.2

115.7

115.9

110

109.6

110.3

H16-C2-H17

107.2

106.9

107.3

C4-N3-H18

109.5

108.9

109.5

N3-C4-C5

108.9

109

109.1

N3-C4-C9

114.8

115

114.8

N3-C4-H19

106.4

106.1

106.1

C5-C4-C9

110.6

110.5

110.5

C5-C4-H19

107.8

107.9

C4-C5-C6

112.2

112.2

C4-C5-H20

108.8

C4-C5-H21 C9-C4-H19

-176.4

179.2

H19-C4-C9-C8

-63.53

-63.38

-63.41

H19-C4-C9-H28

175.50

175.84

175.78

H19-C4-C9-H29

58.96

59.52

59.25

C4-C5-C6-C7

54.82

54.99

54.78

C4-C5-C6-H22

177.58

177.95

177.64

C4-C5-C6-H23

-66.10

-65.79

-66.12

H20-C5-C6-C7

-65.93

-65.40

-65.78

112.4

H20-C5-C6-H22

56.83

57.55

57.08

107.9

109.6

H20-C5-C6-H23

173.15

173.81

173.32

112.1

118.6

H21-C5-C6-C7

176.91

177.33

176.92

108.6

108.7

109.5

H21-C5-C6-H22

-60.33

-59.71

-60.22

109

109

109

109.4

H21-C5-C6-H23

55.99

56.55

56.02

108.1

108

108.1

109.5

C5-C6-C7-C8

-54.34

-54.54

-54.35

112

112

112

112

C5-C6-C7-H24

66.36

66.05

66.30

C4-C9-H28

108.6

108.3

108.4

108.2

C5-C6-C7-H25

-176.87

-177.27

-176.96

-178.5

C4-C9-H29

110.4

110.3

110.3

110.2

H22-C6-C7-C8

-176.82

-177.23

-176.90

-178.4

C6-C5-H20

109.2

109.2

109.2

109.2

H22-C6-C7-H24

-56.12

-56.64

-56.25

C6-C5-H21

110.9

111.2

110.9

110.7

H22-C6-C7-H25

60.64

60.04

60.49

C5-C6-C7

111.7

111.6

111.8

112

H23-C6-C7-C8

66.58

66.23

66.52

C5-C6-H22

109.9

110

109.8

110.7

H23-C6-C7-H24

-172.72

-173.18

-172.83

C5-C6-H23

109.2

109.2

109.1

109.2

H23-C6-C7-H25

C20-C5-H21

106.6

106.5

106.7

C7-C6-H22

110.3

110.4

110.4

C7-C6-H23

109.2

109.2

109.2

C6-C7-C8

111.2

111.2

C6-C7-H24

109.3

109.2

C6-C7-H25

110.3

H22-C6-H23

C2-N3-H18

C4-C9-C8

115

-178.8

109.4

120

-55.96

-56.50

56.09

C6-C7-C8-C9

54.50

54.63

54.53

109.5

C6-C7-C8-H26

177.07

177.45

177.11

109.4

C6-C7-C8-H27

-66.33

-66.02

-66.26

111.2

112

H24-C7-C8-C9

-66.22

-65.97

-66.14

109.3

109.2

H24-C7-C8-H26

56.35

56.84

56.44

110.3

110.2

109

H24-C7-C8-H27

172.94

173.38

173.07

106.4

106.3

106.4

H25-C7-C8-C9

177.07

177.36

177.13

C8-C7-H24

109.3

109.2

109.2

109

H25-C7-C8-H26

-60.37

-59.82

-60.29

C8-C7-H25

110.2

110.3

110.3

110.7

H25-C7-C8-H27

56.23

56.71

56.34

C7-C8-C9

111.7

111.5

111.5

112

-54.94

-55.08

-55.11

C7-C8-C9-C4

179.2

C7-C8-H26

110.4

110.5

110.5

109.2

C7-C8-C9-H28

65.56

65.06

65.14

C7-C8-H27

109.2

109.2

109.2

109.4

C7-C8-C9-H29

-177.84

-178.18

-178.04

-178.5

H24-C7-H25

106.5

106.4

106.5

H26-C8-C9-C4

-177.78

-178.13

-177.99

-178.4

C9-C8-H26

109.9

110.1

109.9

H26-C8-C9-H28

-57.27

-58.00

-57.73

C9-H8-H27

109.2

109.1

109.2

H26-C8-C9-H29

59.32

58.77

59.09

C8-C9-H28

109.4

109.4

109.4

109.4

H27-C8-C9-C4

65.94

65.61

65.71

C8-C9-H29

109.7

110

109.8

109.5

H27-C8-C9-H28

-173.56

-174.26

-174.04

H26-C8-H27

106.4

106.3

106.3

H27-C8-C9-H29

-56.96

-57.49

-57.22

H28-C9-H29

106.6

106.6

106.7

O11-S10-OI2

120.6

121.6

120.5

H11-S10-O13

108.3

108.1

108.5

O12-S10-O13

106.1

106.3

106.9

S10-O13-H30

108.3

104.7

107.8

109

119.3

C1-S10-O13-H30

129.05

128.34

141.73

O11-S10-S13-H30

-116.99

-118.21

-104.78

O12-S10-O13-H30

13.76

13.84

26.61

Table 2: The observed and calculated frequencies of CHES using RHF/cc-pvdz, B3LYP/cc-pvdz and B3LYP/6-311++G(d,p) methods. Theoretical Wavenumbers cm-1

Experimental Wavenumbers cm-1 FTFTIR Raman

Vibrational Assignments with PED

RHF/cc-pvdz

B3LYP/cc-pvdz

B3LYP/6-311++ G(d,p)

Frequency

Intensity

Frequency

Intensity

Frequency

Intensity

3777

4074

207.84

3717

108.27

3773

206.61

OH  (100)

3543

3728

0.75

3463

0.21

3495

128.98

NH  (100)

3303

2.47

3138

1.47

3132

126.99

CH2 asy  (99)

3258

12.66

3080

9.39

3079

112.20

CH2 asy  (92)

3236

1.93

3076

38.60

3072

89.57

CH  (88)

3231

56.66

3073

1.73

3067

87.84

CH2 sym  (84)+ CH  (14)

3218

112.13

3065

77.19

3057

83.63

(CH2)2 asy  (68)+ CH  (10)

3214

35.70

3062

12.94

3054

80.55

CH2 asy  (44) + CH  (42)

3211

80.19

3060

78.43

3051

78.01

CH2 asy  (52) + CH  (36)

3210

70.46

3059

49.19

3050

76.05

CH2 asy  (75) + CH  (10)

3166

75.64

3013

73.88

3010

65.92

(CH2)2 sym  (69)+ CH  (11)

3164

28.58

3009

11.87

3005

57.06

CH2 sym  (42)+ CH  (45)

3160

4.26

3006

20.60

3003

53.57

CH2 sym  (78)

2976

3158

20.61

3003

23.60

2998

41.94

CH  (93)

2923

2938

3158

28.85

2992

11.06

2990

39.78

CH  (88)

2902

2899

3147

27.22

2989

3.55

2987

39.01

CH  (95)

2859

2857

3142

7.79

2976

32.54

2985

37.01

CH  (93)

1574

1538

1648

51.88

1501

19.70

1521

36.47

CH2  (64) + HNC b (17)

1628

1.26

1494

12.97

1508

35.76

HNC b (39) + CH2  (18)

1614

0.55

1481

0.56

1502

34.77

(CH2)5  (87)

1596

7.64

1465

7.45

1495

30.06

(CH2)4  (83)

1595

3.94

1461

3.49

1490

22.23

(CH2)4  (82)

1589

3.24

1459

1.90

1489

22.18

(CH2)2  (79)

1450

1583

0.03

1453

0.03

1484

17.64

(CH2)2  (57)

1419

1562

12.09

1431

5.73

1454

16.51

CH2  (83)

1545

4.40

1402

1.96

1416

16.23

HCC b (10) + HCNC t (18) + HCNC t (17)

1521

30.00

1382

6.74

1393

16.03

HCC b (10) + HCCC t (32)

1509

0.87

1378

14.02

1381

14.38

HCC b (10) +HCCC t (31)

1503

1.63

1375

4.49

1377

14.31

HCC b (16) +HCCC t (28)

1501

1.01

1367

2.05

1370

13.57

CC  (10) + HCC b (29) + HCNC t (18)

3107 3086

3023

3022

1485

1455

1423 1386 1370

1387

1352

1356

1477

1.84

1359

2.15

1367

13.34

HCCC t (50)

1454

206.06

1334

7.11

1348

12.42

HCN b (10) + HCC b (40)

1452

47.31

1327

104.51

1338

11.00

SO2 asy  (49)

1437

4.62

1321

44.16

1333

10.62

SO2 asy  (10) + HCNC t (14) + HCCC t (23)

1417

28.11

1301

36.69

1313

9.98

HCC b (10) + HCNC t (16)

1390

9.68

1280

3.47

1289

9.57

HCC b (71)

1257

1257

1386

6.80

1278

2.78

1288

9.08

HCC b (12) + HCCC t (30)

1233

1234

1382

3.47

1273

3.49

1284

9.07

HCC b (14) + HCCC t (10)

1366

10.59

1237

14.82

1269

8.66

HCC b (13) + HCN b (15) + HCCN t (39)

1311

7.04

1207

3.93

1216

8.54

HCC b (12)

1302

6.23

1199

5.42

1204

8.50

HCC b (10)

1278

188.88

1160

46.80

1166

7.82

CN  (50) + HOS b (15) + SO  (10)

1258

93.74

1155

134.60

1149

7.44

SO  (16) + HOS b (22)

1235

52.71

1132

85.18

1132

7.39

HOS b (12) + HCN b (11) + HCC b (14)

1207

80.42

1110

1.62

1099

7.19

CC  (63)

1199

5.10

1092

2.88

1095

6.92

SO2 sym  (58) + HOS b (20)

1176

2.41

1087

62.83

1087

5.53

SO2 sym  (57) + HOS b (30)

1162

0.35

1084

7.74

1084

5.43

CN  (17)

1140

5.11

1066

0.60

1066

5.25

CC  (11)

1128

4.25

1055

1.75

1051

4.98

CC  (47)

1114

12.40

1043

1.13

1038

4.56

CC  (33)

1108

0.97

1018

7.33

1030

4.06

HCCN b (21) + HCNC b (11)

1054

5.00

978

3.00

974

3.92

CN  (16)

998

0.13

933

0.17

931

3.65

CC  (24) + HCCC t (10)

967

1.58

906

3.94

903

3.59

CC  (21)

963

7.36

898

7.18

897

3.54

HCC b (10)

934

218.41

857

0.48

851

3.42

CC  (27) + CCC b (10) + HCCC t (13)

908

18.03

815

7.71

809

3.00

CC  (30)

872

27.43

802

140.96

795

2.75

CS  (15) + SO  (18) + HCC b (10)

853

0.70

793

4.41

792

2.35

CC  (10) + HCCC t (28)

847

6.94

775

32.60

776

2.31

CS  (12) + HCC b (14) + HNCC t (11)

822

3.57

752

31.95

734

2.31

SO  (13) + HNCC t (26)

1221 1183

1186

1154 1130

1131

1098

1084 1036 1031

1037

955 923 903 897

896

830 804

806

790 775

777

756 616

612

807

47.07

698

57.83

689

2.11

CS  (20) + SO  (50)

569

562

636

85.11

577

29.77

580

1.96

CCC b (13) + SO2  (10)

538

520

589

37.07

527

38.33

535

1.94

SO2  (19) +SCC b (13) + OCOS  (14)

536

22.44

491

13.22

492

1.87

CNC b (20)

521

31.54

465

7.38

468

1.86

CCC b (15) + NCCC  (20)

496

5.33

448

5.88

458

1.66

CCC b (18) +SO2  (11) + OCOS  (16)

442

475

0.30

443

11.46

446

1.51

CCC b (11) + SO2  (27) + OCOS  (15)

405

465

18.70

412

13.66

421

1.45

CS  (10) + SO2  (29) + OCOS  (10)

428

8.07

383

8.87

394

1.25

SO2  (36) + OCOS  (12)

362

4.55

338

0.70

336

1.18

HCCC t (11) + CCCC t (19)

520 488

473

342

207

69

350

10.60

317

19.53

324

0.90

NCC b (20) + SO2 t (21) +OCOS  (16)

335

12.31

302

10.33

298

0.90

SO2 t (23) + HOSC t (12) + OCOS  (37)

248

0.36

239

0.22

236

0.68

HCCC t (21) + CCCC t (24)

231

4.88

215

2.80

212

0.65

CCCC t (23)

220

0.77

203

0.95

202

0.52

CC  (10) + CN  (10) + CS  (16) +CCN b (22)

173

103.29

159

73.79

151

0.50

SO2 t (11) + HOSC t (72)

161

4.41

150

6.96

118

0.49

SCC b (26) + CCCC t (12)

125

3.02

115

2.04

102

0.44

CNCC t (16) +OSCC t (30) + SCCN t (17)

111

1.70

103

1.59

93

0.32

CCNC t (10) + SCCN t (14) + OSCC t (29)

62

0.92

62

0.76

63

0.30

SCC b (21) + CNC b (26) + CCN b (20)

40

1.50

41

1.56

43

0.12

CCNC t (39) + SCCN t (32)

28

0.77

31

0.26

30

0.06

CNCC t (24) +OSCC t (24) + SCCN t (26) + CCNC t (21)

sym= symmetric, asy= asymmetric, = stretching, = scissoring, b= bending, = out of plane bending, t= torsion

Table 3. Experimental and calculated absorption wavelength (λ), excitation state, oscillator strength(f), electronic absorption value (eV) and transition of CHES by TD-DFT method (B3LYP/cc-pVDZ) Excitation

Excited state 1 5657 Excited state 2 56 58 56 59 56 60 Excited state 3 56 58 56 59 56  60 56 61 56 62

Singlet A

Cal. Wavelength Oscillator Electronic Wavelength(nm) (nm) Strength(f) Absorption value (eV)

Transition

258.29

0.018

4.8003

HOMO ↔ LUMO (98%)

0.67434 0.12952 -0.107

220.1

0.0094

5.6331

HOMO ↔ LUMO+1 (91%) HOMO ↔ LUMO+2 (3%) HOMO ↔ LUMO+3 (2%)

-0.1527 0.63217 -0.1607 -0.1516 -0.1070

207.18

0.0031

5.9843

HOMO ↔ LUMO+1 (5%) HOMO ↔ LUMO+2 (80%) HOMO ↔ LUMO+3 (5%) HOMO ↔ LUMO+4 (5%) HOMO ↔ LUMO+5 (2%)

0.69905

235

Table 4 : Mulliken atomic charges of CHES by RHF/cc-pVDZ and B3LYP/cc-pVDZ methods. Atoms

B3LYP

RHF

C1 C2 N3 C4 C5 C6 C7 C8 C9 S10 O11 O12 O13 H14 H15 H16 H17 H18 H19 H20 H21 H22 H23 H24 H25 H26 H27 H28 H29 H30

-0.1622 0.1006 -0.2357 0.0051 0.0643 0.0018 0.0027 0.0031 0.0633 0.9384 -0.4197 -0.4317 -0.3123 0.0878 0.0678 -0.0094 0.0382 0.0716 -0.0141 -0.0105 -0.0011 -0.0003 0.0006 0.0019 -0.0002 -0.0002 -0.0004 -0.0098 -0.0073 0.1689

-0.2373 0.1435 -0.4510 0.0358 0.0147 -0.0539 -0.0504 -0.0535 0.0151 1.3427 -0.5748 -0.5748 -0.4416 0.1238 0.1010 0.0117 0.0669 0.1125 0.0223 0.0162 0.0310 0.0324 0.0245 0.0260 0.0313 0.0316 0.0236 0.0167 0.0239 0.2056

Table 5 : The Calculated Thermodynamic parameters of CHES

Parameter Zero point vibrational energy(Kcal/Mol) Rotational constant (GHz)

Rotational temperatures (Kelvin)

Entropy (Cal/Mol-Kelvin) Total Translational Rotational Vibrational Molar capacity at constant volume (Cal/Mol-Kelvin ) Total Translational Rotational Vibrational Energy (KCal/Mol) Total Translational Rotational Vibrational

RHF/

B3LYP/

B3LYP/

cc-pVDZ

cc-pVDZ

6-311++G(d,p)

173.2177 2.09472 0.23243 0.22253 0.10053 0.01115 0.01068

161.2169 2.02003 0.22956 0.21999 0.09695 0.01102 0.01056

161.666 2.04825 0.2293 0.2196 0.0983 0.011 0.01054

117.581 41.888 32.362 43.331

120.791 41.888 32.422 46.481

121.582 41.888 32.411 47.283

49.126 2.981 2.981 43.164

53.261 2.981 2.981 47.299

53.181 2.981 2.981 47.22

181.55 0.889 0.889 179.772

170.112 0.889 0.889 168.334

170.614 0.889 0.889 168.836

Table 6: Temperature dependence of thermodynamic properties of CHES

T (K) 100 200 298.15 300 400 500 600 700 800 900 1000

S (J/mol.K) 336.36 427.36 505.5 506.93 583.26 657.03 727.41 793.94 856.61 915.61 971.21

Cp (J/mol.K)

ddH (kJ/mol)

103.39 165.76 231.16 232.44 300.72 360.98 410.92 452.06 486.34 515.29 539.97

6.79 20.28 39.7 40.12 66.82 99.99 138.67 181.88 228.85 278.97 331.77

Table 7: The electric dipole moment (μ), polarizability (α), and first hyperpolarizability (β) of CHES

RHF/cc-pVDZ

B3LYP/cc-pVDZ

-24

αxx αxy αyy αxz αyz αzz αtot ∆α μx μy μz μ

a.u. esu(x 10 ) 132.742 19.672 βxxx 0.560 0.083 βxxy 103.766 15.378 βxyy -1.389 -0.206 βyyy -1.789 -0.265 βxxz 100.611 14.911 βxyz 111.500 16.524 βyyz 231.951 34.375 βxzz 2.529 0.375 βyzz 0.897 0.133 βzzz 0.146 0.022 βtot 2.688 0.398

-33

92.406 23.1512 35.2653 7.8773 -27.6488 0.5134 9.5767 34.3253 10.9206 24.5721 167.466

esu(X10 ) 798.295 200.003 304.657 68.052 -238.858 4.435 82.733 296.536 94.343 212.278 1446.739

αxx αxy αyy αxz αyz αzz αtot ∆α μx μy μz μ

123.9975 -5.8741 107.018 18.1167 -4.4039 132.7474 121..2543 215.9597 -1.1305 -0.2796 -2.0097 2.3227

esu(X10-24) esu(X10-33) 18.376 βxxx 85.077 734.984 -0.871 βxxy -19.369 -167.327 15.860 βxyy -40.744 -351.987 2.685 βyyy -19.784 -170.910 -0.653 βxxz 45.157 390.113 19.673 βxyz -7.503 -64.817 0.148 βyyz -30.121 -260.217 32.005 βxzz 6.456 55.773 -0.168 βyzz -3.317 -28.659 -0.041 βzzz -96.473 -833.426 -0.298 βtot 104.953 906.689 0.344

Table 8 : Chemical shift (13C &1H) for CHES *δ(ppm)+ Atoms Expt. Chemical Shift C1 57.013 C2 47.95 C4 48.122 C5 47.781 C6 47.441 C7 40.659 C8 46.401 C9 47.61 H14 3.453 H15 3.44 H16 3.427 H17 3.337 H18 1.243 H19 3.334 H20 2.179 H21 3.331 H22 3.328 H23 2.134 H24 2.119 H25 3.325 H26 3.177 H27 1.908 H28 1.901 H29 3.169 H30 4.601

B3LYP/cc-pVDZ Absolute Chemical shielding Shift 132.495 67.491 146.332 53.654 135.407 64.578 150.169 49.817 159.462 40.523 160.680 39.306 159.351 40.634 150.071 49.914 28.057 4.541 28.343 4.255 28.460 4.138 27.767 4.831 32.280 0.318 29.287 3.310 30.535 2.062 28.962 3.635 29.302 3.295 29.944 2.653 30.188 2.410 29.501 3.097 29.311 3.287 29.948 2.650 30.528 2.070 29.043 3.555 27.121 5.477

RHF/cc-pVDZ ∆ Absolute Chemical shielding Shift 10.478 148.345 51.6401 5.704 162.761 37.2239 16.456 152.003 47.982 2.036 164.335 35.6506 6.918 173.517 26.4684 1.353 174.570 25.415 5.767 173.472 26.5134 2.304 164.156 35.8293 1.088 28.486 4.1112 0.815 28.937 3.6603 0.711 29.439 3.1583 1.494 28.516 4.0816 0.925 32.631 -0.0334 0.024 29.959 2.6382 0.117 30.946 1.6518 0.304 29.574 3.024 0.033 29.946 2.6517 0.519 30.558 2.0398 0.291 30.707 1.8907 0.228 30.075 2.5225 0.110 29.960 2.6378 0.742 30.575 2.023 0.169 30.945 1.6528 0.386 29.691 2.9067 0.876 27.778 4.8196

∆ (δ exp -δ cal): difference between respective chemical shifts.

∆ 5.373 10.726 0.140 12.130 20.973 15.244 19.888 11.781 0.658 0.220 0.269 0.745 1.276 0.696 0.527 0.307 0.676 0.094 0.228 0.803 0.539 0.115 0.248 0.262 0.219

Table 9: Second order perturbation theory analysis of Fock matrix in NBO analysis.

Donor(i) Type

Acceptor(j) Type

                              LP(1) LP(1) LP(2) LP(3)

                                 

C1-C2 C1-S10 C1-H14 C1-H15 C2-N3 C2-H16 C2-H17 N3-C4 N3-H18 C4-C5 C4-C9 C4-H19 C5-C6 C5-H20 C5-H21 C6-C7 C6-H22 C6-H23 C7-C8 C7-H24 C7-H25 C8-C9 C8-H26 C8-H27 C9-H28 C9-H29 S10-O11 S10-O12 S10-O13 O13-H30 N3 O11 O11 O11

N3-C4 S10-O13 C2-H16 C2-H17 C1-S10 C1-H14 C1-H15 C5-C6 C4-H19 C9-H29 C5-H21 N3-H18 N3-C4 C4-H19 C4-C9 C5-H21 C4-C5 C5-H20 C6-H22 C6-H23 C5-C6 N3-C4 C6-C7 C7-H24 C4-H19 C4-C5 S10-O12 S10-O13 S10-O11 S10-O11 C2-H16 S10-O13 S10-O12 S10-O13

E KJ/mol)

E(j)a-E(i)b (a.u.)

F(i,j)c (a.u.)

3.19 4.91 3.42 3.36 2.25 3.31 3.38 2.09 2.13 2.1 2.07 4.41 2.62 3.58 4.16 2.11 3.79 3.67 2.12 3.45 4.01 2.62 3.9 3.57 3.56 4.14 1.89 3.45 6 1.62 8.1 1.1 17.44 38.23

1.05 0.76 0.95 0.97 0.89 0.91 0.9 1.14 1.05 1.03 1.04 0.91 0.99 0.91 0.87 1.03 0.87 0.9 1.03 0.91 0.88 0.99 0.88 0.91 0.91 0.87 1.26 1.02 1.1 1.09 0.63 0.82 0.56 0.33

0.052 0.059 0.051 0.051 0.042 0.049 0.049 0.044 0.042 0.042 0.042 0.057 0.046 0.051 0.054 0.042 0.052 0.051 0.042 0.05 0.053 0.046 0.052 0.051 0.051 0.054 0.045 0.058 0.074 0.039 0.065 0.029 0.089 0.103

(2)

LP(1) LP(2) LP(3) LP(1) LP(2)    

O12 O12 O12 O13 O13 C1-S10 S10-O11 S10-O12 S10-O13

        

C1-S10 S10-O11 S10-O13 S10-O11 S10-O12 C2-N3 C1-C2 C1-H15 O13-H30

1.22 17.19 39.58 2.94 6.61 0.59 1.4 1.68 2.03

0.92 0.55 0.32 0.92 0.64 0.23 0.09 0.11 0.39

0.031 0.088 0.104 0.048 0.059 0.033 0.036 0.041 0.059

Table 10: Calculated atomic charges of CHES by Natural Bond Orbital analysis and Mulliken Charge Analysis by B3LYP/cc-pVDZ method Atom Natural charge Mulliken charge C1 C2 N3 C4 C5 C6 C7 C8 C9 S10 O11 O12 O13 H14 H15 H16 H17 H18 H19 H20 H21 H22 H23 H24 H25 H26 H27 H28 H29 H30

-0.6702 -0.2107 -0.7557 -0.0201 -0.4425 -0.4367 -0.4360 -0.4364 -0.4422 2.3187 -0.8983 -0.9230 -0.8889 0.2771 0.2585 0.1815 0.2202 0.3863 0.2226 0.2100 0.2314 0.2303 0.2102 0.2105 0.2293 0.2298 0.2098 0.2105 0.2276 0.4964

-0.1622 0.1006 -0.2357 0.0051 0.0643 0.0018 0.0027 0.0031 0.0633 0.9384 -0.4197 -0.4317 -0.3123 0.0878 0.0678 -0.0094 0.0382 0.0716 -0.0141 -0.0105 -0.0011 -0.0003 0.0006 0.0019 -0.0002 -0.0002 -0.0004 -0.0098 -0.0073 0.1689

Table 11: HOMO-LUMO energy value, Ionization potential and Chemical hardness of CHES method calculated by B3LYP/cc-pVDZ method

Parameter Energy (eV) EHOMO ELUMO ELUMO+1 ELUMO+2 ELUMO+3 ELUMO+4 ELUMO+5

Parameter -5.8047 -0.2337 0.8438 1.1774 1.3091 1.5755 1.8803

Ionization potential (μ) Chemical Hardness (η) Softness (S) Electronegativity (χ) Electrophilicity index (w )

-3.0192 2.7855 0.1795 3.0192 1.6362

Table 12: Using Mulliken population analysis, Fukui functions, local softness and local electrophilicity indices in eV for CHES

Atoms

Mulliken atomic charges

Fukui functions

Local softness

qN+1

qN

qN-1

fk+

C1

-0.6957

-0.6701

-0.6846

-0.0256

0.01447

-0.0055

-0.0046

0.00260

C2

-0.2694

-0.2106

-0.2132

-0.0588

0.00255

-0.0281

-0.0105

N3

-0.2755

-0.7556

-0.7582

0.48008

0.00263

0.24136

C4

-0.0534

-0.0200

-0.0130

-0.0333

-0.0069

C5

-0.4411

-0.4424

-0.4386

0.00129

-0.0038

C6

-0.4342

-0.4367

-0.4318

0.00248

C7

-0.4446

-0.4359

-0.4296

C8

-0.4339

-0.4364

Local electrophilicity indices

fk-

fk0

Sk+

Sk-

Sk

0

wk+

wk-

wk0

-0.0010

-0.0419

0.02368

-0.0091

0.00046

-0.0050

-0.0962

0.00417

-0.0460

0.08617

0.00047

0.04332

0.78551

0.00430

0.39491

-0.0201

-0.0059

-0.0012

-0.0036

-0.0546

-0.0114

-0.0330

-0.0012

0.00023

-0.0006

-0.0002

0.00211

-0.0062

-0.0020

-0.0048

-0.0012

0.00045

-0.0008

-0.0002

0.00406

-0.0079

-0.0019

-0.0087

-0.0063

-0.0075

-0.0015

-0.0011

-0.0013

-0.0142

-0.0103

-0.0122

-0.4316

0.00246

-0.0047

-0.0011

0.00044

-0.0008

-0.0002

0.00403

-0.0078

-0.0018

C9

-0.4409

-0.4421

-0.4385

0.00126

-0.0036

-0.0012

0.00023

-0.0006

-0.0002

0.00206

-0.0059

-0.0019

S10

2.30710

2.31872

2.21629

-0.0116

0.10243

0.04541

-0.0020

0.01839

0.00815

-0.0190

0.16760

0.07429

O11

-0.8500

-0.8983

-0.9776

0.04825

0.07934

0.06380

0.00866

0.01424

0.01145

0.07895

0.12982

0.10438

O12

-0.8881

-0.9229

-0.9863

0.03487

0.06336

0.04912

0.00626

0.01137

0.00882

0.05705

0.10367

0.08036

O13

-0.8640

-0.8889

-0.9530

0.02487

0.06411

0.04449

0.00446

0.01151

0.00799

0.04069

0.10490

0.07279

H14

0.29348

0.27709

0.19020

0.01639

0.08689

0.05164

0.00294

0.01560

0.00927

0.02682

0.14217

0.08449

H15

0.27573

0.25848

0.22099

0.01725

0.03749

0.02737

0.00310

0.00673

0.00491

0.02822

0.06134

0.04478

H16

0.26032

0.18148

0.10826

0.07884

0.07322

0.07603

0.01415

0.01314

0.01365

0.12900

0.11980

0.12440

H17

0.29242

0.22015

0.17830

0.07227

0.04185

0.05706

0.01297

0.00751

0.01024

0.11825

0.06847

0.09336

H18

0.43180

0.38628

0.36970

0.04552

0.01658

0.03105

0.00817

0.00298

0.00557

0.07448

0.02713

0.05080

H19

0.26326

0.22257

0.20702

0.04069

0.01555

0.02812

0.00730

0.00279

0.00505

0.06658

0.02544

0.04601

H20

0.23408

0.21003

0.19815

0.02405

0.01188

0.01797

0.00432

0.00213

0.00322

0.03935

0.01944

0.02939

H21

0.25895

0.23142

0.20430

0.02753

0.02712

0.02733

0.00494

0.00487

0.00490

0.04504

0.04437

0.04471

H22

0.27296

0.23032

0.20075

0.04264

0.02957

0.03611

0.00765

0.00531

0.00648

0.06977

0.04838

0.05908

H23

0.22914

0.21020

0.18955

0.01894

0.02065

0.01980

0.00340

0.00371

0.00355

0.03099

0.03379

0.03239

H24

0.22520

0.21047

0.19615

0.01473

0.01432

0.01453

0.00264

0.00257

0.00261

0.02410

0.02343

0.02377

H25

0.25954

0.22932

0.18601

0.03022

0.04331

0.03677

0.00542

0.00777

0.00660

0.04945

0.07086

0.06015

H26

0.27233

0.22975

0.20206

0.04258

0.02769

0.03514

0.00764

0.00497

0.00631

0.06967

0.04531

0.05749

H27

0.22869

0.20975

0.18786

0.01894

0.02189

0.02042

0.00340

0.00393

0.00366

0.03099

0.03582

0.03340

H28

0.23451

0.21046

0.19720

0.02405

0.01326

0.01866

0.00432

0.00238

0.00335

0.03935

0.02170

0.03052

H29

0.25525

0.22762

0.19813

0.02763

0.02949

0.02856

0.00496

0.00529

0.00513

0.04521

0.04825

0.04673

H30

0.49672

0.49640

0.30568

0.00032

0.19072

0.09552

0.00006

0.03423

0.01715

0.00052

0.31206

0.15629

GRAPHICAL ABSTRACT

HIGHLIGHTS     

Optimized geometry and vibrational assignments with PED were computed by DFT. NBO, NMR and UV spectral analysis were carried out. HOMO – LUMO and MEP analysis were made. Isotropic chemical shifts were calculated using the GIAO method. Local reactivity descriptor such as Fukui functions was calculated.

DFT analysis on the molecular structure, vibrational and electronic spectra of 2-(cyclohexylamino)ethanesulfonic acid.

The FTIR and FT-Raman spectra of 2-(cyclohexylamino)ethanesulfonic acid were recorded in the regions 4000-400 cm(-1) and 4000-50 cm(-1) respectively. ...
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