Accepted Manuscript Molecular structure, Spectroscopic characterization of (S)-2-Oxopyrrolidin -1yl Butanamide and ab-initio, DFT based quantum chemical calculations T. Ramya, S. Gunasekaran, G.R. Ramkumaar PII: DOI: Reference:

S1386-1425(15)00505-3 http://dx.doi.org/10.1016/j.saa.2015.04.033 SAA 13584

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

10 November 2014 31 March 2015 16 April 2015

Please cite this article as: T. Ramya, S. Gunasekaran, G.R. Ramkumaar, Molecular structure, Spectroscopic characterization of (S)-2-Oxopyrrolidin -1-yl Butanamide and ab-initio, DFT based quantum chemical calculations, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa. 2015.04.033

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Molecular structure, Spectroscopic characterization of (S)-2-Oxopyrrolidin -1-yl Butanamide and ab-initio, DFT based quantum chemical calculations T.Ramyaa,d, S.Gunasekaranb, G.R.Ramkumaarc* a

Department of Physics, C.T.T.E College for Women, Perambur, Chennai - 600095, TN, India.

b

Research and Development, St. Peter’s Institute of Higher Education and Research, St. Peter’s University, Avadi, Chennai – 600054, TN, India.

c

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

PG and Research Department of Physics, Pachaiyappa’s College, Chennai-600030, TN, India.

*Corresponding Author (email: [email protected]) Tel.: +91 9884351008

Abstract The experimental and theoretical spectra of (S)-2-Oxopyrrolidin -1-yl Butanamide (S2OPB) were studied. FT-IR and FT-Raman spectra of S2OPB in the solid phase were recorded and analyzed in the range 4000 – 450 and 5000 – 50 cm-1 respectively. The structural and spectroscopic analyses of S2OPB were calculated using Ab-initio Hartree Fock (HF) and Density Functional Theory calculations (B3PW91, B3LYP) with 6-31G(d,p) basis set. A complete vibrational interpretation has been made on the basis of the calculated Potential Energy Distribution (PED). The HF, B3LYP and B3PW91 methods based NMR calculation has been used to assign the 1H NMR and 13C NMR chemical shift of S2OPB. Comparative study on UVVis spectral analysis between the experimental and theoretical (B3PW91, B3LYP) methods and the global chemical parameters and local descriptor of reactivity through the Fukui function were performed. Finally the thermodynamic properties of S2OPB were calculated at different

temperatures and the corresponding relations between the properties and temperature were also studied. Keywords : S2OPB; vibrational spectra; NMR; UV-Vis; DFT Introduction (S)-2-Oxopyrrolidin-1-yl Butanamide (S2OPB) belongs to antiepileptic or anticonvulsant drug group used in the treatment of epileptic seizures, bipolar diseases and as a mood stabilizer [1]. S2OPB is a prototypical nootropic S-enantiomer of etiracetum. Which belongs to pyrrolidine derivative group and second-generation antiepileptic drug that does not alter basic cell characteristics and normal neurotransmission. S2OPB has no inhibitory effect on sodium or lowvoltage-activated, T-type calcium channels in neocortical neurons [2] and does not have a high affinity for GABA, N-methyl d-aspartate (NMDA) or glutamate receptors. However, it affects intraneuronal Ca2+ levels by partial inhibition of N-type Ca2+ currents and by reducing the release of Ca2+ from intra neuronal stores. In addition, it partially reverses the reductions in GABA and glycine-gated currents induced by zinc and β-carbolines. S2OPB reduces high-voltage, N-type, calcium channel currents in neurons, but do not have an effect on L-type, P-type or Q-type calcium channels [2, 3]. This effect occurs within a few seconds and suggests a direct interaction of S2OPB with the N-type channel and binds to a synaptic vesicle protein SV2A [4] which impede nerve conduction across synapse [5] rather than a second messenger pathway. This interesting information leads to the present investigation. A literature survey reveals that to the best of our knowledge no HF/DFT and structural parameter calculation of S2OPB has been reported so far. Therefore the present investigation is undertaken to study the vibrational spectra of S2OPB in detail and to identify the various normal modes with greater wave number

accuracy, HOMO and LUMO energy difference, natural bonding orbital (NBO) and Fukui function analysis. Experimental The compound S2OPB in powder form was procured from a reputed Pharmaceutical company, Chennai, India with more than 99% purity and used as such for the spectral recording. FT-IR spectrum of the title compound has been recorded in the range 4000 - 450 cm -1 in the solid state. The FT-Raman spectrum of S2OPB was recorded in the range 5000 - 50 cm

-1

on a

computer interfaced BRUKER IFS 66V model Interferometer. UV-Visible spectral measurements have been made using Cary 5E –UV-VIS spectrophotometer in the wavelength region 200-400 nm. All sharp bands observed in the spectra are expected to have an accuracy of ±1cm-1. The spectral measurements were carried out at the Indian Institute of Technology (IIT) Madras (Tamil Nadu), India. Computational details All the theoretical computations were performed at Hartree Fock, B3PW91 and B3LYP level on a Pentium IV/1.6 GHz personal computer using the Gaussian 03W program package [6]. The geometry optimization was carried out using the initial geometry generated from standard geometrical parameters at HF, B3PW91 and B3LYP methods adopting 6-31G(d,p) basis set to characterize all stationary points as minima. In the quantum methods, Becke’s three parameter exchange–functional (B3) [7, 8] combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) [9] by implementing the split-valance polarized 6-31G(d,p) basis set has been utilized for the computation of molecular structure optimization and vibrational frequencies. The optimized geometry was used in the vibrational frequency calculations at the HF, B3PW91 and B3LYP level to characterize all stationary points as minima. Finally,

calculated normal mode vibrations wave numbers provides thermodynamic properties by way of statistical mechanics. The vibrational frequency assignments were made with a high degree of accuracy with the help of the Chemcraft software program [10]. Result and Discussion Geometry optimization The calculated geometrical parameters such as bond lengths and bond angles were compared with available experimental data. As the experimental values of S2OPB

are known, the

theoretically calculated values may supply an idea about the geometry of the molecule and also an idea of how the geometry of the molecule changes from one basis set to another. The optimized structural parameters of S2OPB determined from the ab initio HF/6-31G(d,p), B3WP91/6-31G(d,p) and B3LYP/6-31G(d,p) calculations and also the available experimental values are listed in Tables 1 and 2, in accordance with the atom numbering scheme given in Fig.1. A statistical treatment of these data shows that, for the bond lengths, B3LYP/6-31G(d,p) and

B3WP91/6-31G(d,p) is better than the HF/6-31G(d,p) geometry. The correlation

coefficients for bond lengths computed from the ab initio-HF, DFT- B3PW91 and B3LYP methods with the experimental values were found to be 0.9965, 0.9972 and 0.9973 respectively. Similarly, the correlation coefficients for bond angles computed from the HF and DFT methods with the experimental values were found to be 0.9347, 0.9270 and 0.9332 respectively. The agreement for bond angles is not as good as that for the bond length. The slight variation with the experimental value is due to the fact that optimization is performed in an isolated condition, whereas the crystal environment affected the experimental X-ray structure.

Vibrational spectral analysis In the present study, we have performed a complete frequency calculation analysis in terms of fundamental, overtone and combination bands using HF/6-31G(d,p), B3WP91/631G(d,p) and B3LYP/6-31G(d,p) basis set. The complete vibrational assignments of most of the fundamental vibration of S2OPB were straightforward on the basis of their calculated Potential Energy Distribution (PED). According to the theoretical calculations, S2OPB has a non-planar structure of C1 point group symmetry. The molecule of S2OPB consists of 26 atoms, so it has 72 normal vibrational modes active in both IR and Raman. Since the tittle molecule possess C1 point symmetry, all the modes of vibrations belong to A species only. The measured wave numbers from FT-IR and FT-Raman spectra and PED calculations were compared with the wave numbers assigned by HF, B3WP91 and B3LYP with 6-31G(d,p) basis set. A good relevance is revealed between these compared values. The experimental and theoretical FT-IR and experimental FTRaman spectra are shown in Figs. 2 and 3. The calculated and experimental wave numbers and intensities of the normal mode of vibrations and the corresponding vibrational assignment of S2OPB are given in Table 3. Heterocyclic ring vibrations Heterocyclic ring in the present compound is a five member nitrogen substituted pyrolidine ring. In heterocyclic compounds C-H vibrational bands are usually weak. In many cases it is too weak for detection. In the present investigation the band at 3020 cm-1 in FT-IR spectrum and the corresponding theoretical vibrations are at 3030 and 3019 cm-1 corresponds to C-H vibrations of the pyrolidine ring. The other heterocyclic vibrations are C-C stretching vibrations. These vibrations are presented in the Table 3.

N-H vibrations The vibration for N-H stretching always occur in the region 3450-3250 cm-1 [11]. In the present study the FT-IR band observed at 3353 and 3179 cm-1 are assigned to N-H asymmetric and symmetric stretching vibrations respectively. The theoretically assigned N-H vibrations are at 3564 and 3405 cm-1. The PED for this mode suggests that this is a pure mode with 99%. The N-H in and out of plane bending vibrations shows that they are not in pure mode. Methyl vibrations The CH3 methyl group in S2OPB has nine fundamental Vibrational assignments. The CH stretching usually occurs in the region 3100-2900 cm-1[12]. The asymmetric stretching usually occurs at higher wavenumber than the symmetric stretching. The CH3 asymmetric stretching mode is predicted theoretically at 3014, 3012 and 2992 cm-1. In FT-IR spectrum, it corresponds to bands at 2994 and 2990 cm-1 and at 2990 cm-1 in FT-Raman. The symmetric mode is at 2942 cm-1 in FT-IR spectrum. S2OPB shows a 97 % PED contribution, suggesting that it is a pure stretching mode. If we consider PED calculations for bending vibrations it shows pure modes for in plane bending vibrations and found to be true by considering the experimental values from FT-IR and FT-Raman spectrum. Methylene vibrations Basically six fundamental vibrations are associated with CH2 group. The asymmetrical and symmetrical stretching vibrations will appear around 3000 cm-1 and in the region 30002900cm-1 respectively [13]. The asymmetric stretching vibrations of S2OPB are observed at 2994 and 2990 cm-1 and symmetric stretching vibrations at 2974, 2965 and 2911 cm-1 in FT-IR spectrum. This mode is calculated in the range 3076 cm-1 with HF/6-31G(d,p) and 2935 cm-1 with B3WP91/6-31G(d,p) and 2926 cm-1 with B3LYP/6-31G(d,p) method. As expected these

modes are pure stretching modes with contribution 99% by PED method. Methylene group normally has deformation vibrations in the region 1465-1440 cm-1 and around 1600 cm-1.The band at 1489, 1457, 1414 cm-1 in FT-IR and 1463, 1447, 1414 cm-1 in FT-Raman are assigned to CH2 in plane bending vibrations. C-N vibrations Identification of C-N vibrations is a very difficult task [14, 15]. In the present work, the band observed in 1121, 1011, 881 cm-1 in FT-IR and 1122 cm-1 in FT-Raman have been assigned to C-N stretching vibration. The calculated band at 1191, 1010 and 870 cm-1 is in good agreement with experimental values. The PED suggests 48% for this mode of vibration. C=O vibrations The C=O stretching vibration band can be easily identified from the FT-IR and FTRaman spectrum because of the degree of conjugation, the strength and polarizations are increasing. Strong band in the region 1715-1680 cm-1 are attributed to C=O stretching [16]. The stretching at 1710 and 1678 cm-1 in FT-IR and 1650 cm-1 in FT-Raman and the theoretical bands at 1739 and 1754 cm-1 corresponds to the C=O stretching fundamentals. The Out of plane O-CN-C deformation occurs in the region 850 to 550 cm-1 and O-C-N occurs at 653 and 387 cm-1 theoretically. Its PED value is 63%. C-C vibrations The carbon-carbon stretching modes are expected in the range from 1260-800 cm-1 [17]. In the present work the wave numbers observed in the FT-IR spectrum at 1168, 1042, 1101 and 943 cm-1 and 935 cm-1 in FT-Raman spectrum have been assigned to C-C stretching. The corresponding theoretically computed values at 1162, 1048, 1020, 1010 and 951 cm-1 shows close agreement with experimental data. The PED of this mode is 59%. The PED of this mode

suggests that this is a mixed mode. The in plane bending modes are observed at 579, 361, 166, 162 cm-1 theoretically. The experimental band in FT-IR spectrum is at 584 cm-1 and in FTRaman at 349 cm-1. Natural population analysis The calculation of effective atomic charges plays an important role in the application of quantum mechanical calculations to molecular systems [18]. The calculated natural atomic charge values form the natural population analysis (NPA) and Mulliken population analysis (MPA) procedures using HF and DFT methods are listed in Table 4 and the graphical representation of the molecule is given in Fig. 4. The NPA from the natural bonding orbital (NBO) method is better than the MPA scheme. The NPA analysis of S2OPB shows high negativity on O12 and O5 which is due to the high positive charge on the carbon atom C8 and C1. The high positive charge possessed by H19 and H20 in the amide molecule is due to the high positive charge on the N6. The presence of lower negative charge on N7 is due to the attraction of negative charge from C2 and C11. HOMO LUMO analysis Many organic molecules that contain conjugated π electrons are characterized by hyper polarizabilities and were analyzed by means of Vibrational spectroscopy [19]. Highest occupied molecular orbital (HOMO) indicating the ability to donate an electron and the lowest unoccupied molecular orbital (LUMO) the ability to accept an electron. Recently the energy gap between HOMO and LUMO has been used to prove the intra molecular charge transfer from the donor to accepter group through a single – double bond conjugated path can induce large variations of both the molecular dipole moment and the molecular polarizability, making activity strong in both IR and Raman. In the present compound HOMO is located at the methylene C-H bond. In

contrast the LUMO is delocalized over the pyrolidine ring. Hence the transfer of electron takes place between methylene and pyrolidine ring structure. HOMO–LUMO energy gap difference of S2OPB by B3LYP/6-31G(d,p) level is shown below and also presented in the Fig. 5. The HOMO energy = -6.2948 eV. The LUMO energy = -0.3517 eV. Energy gap between HOMO and LUMO = -5.9431 eV. The electron density contour map of S2OPB which represents the two dimension projections of cube data into a plane is shown in Fig. 6. 1

H-NMR and 13 C NMR chemical shift assignments The 1H-NMR and

13

C NMR simulated theoretically with the aid of ChemDraw Ultra 10.0

and Table 5 gives the predicted chemical shift values of S2OPB obtained by RHF, B3PW91, B3LYP and ChemDraw Ultra 10.0 software package and its assignment along with shielding values [20]. Figs. 7 and 8 gives the overlay spectrum of S2OPB between experimental and theoretical 1H-NMR and

13

C NMR predicted by HF, B3LYP and B3PW91 methods. In general,

highly shielded electrons appear downfield and vice versa. The present study reveals that the predicted chemical shift values by the theoretical methods both by HF, B3LYP and B3PW91 are slightly deviates from the computed values of ChemDraw Ultra. The spectrum of S2OPB showed a singlet at 3.39 ppm and at 6.49 ppm due to a hydrogen atom of pyrrolidin-2-one group and primary amide respectively. Three doublet peaks at 2.49 ppm for the pyrrolidin ring of hydrogen atoms H21 and H22 and another doublet at 4.46 ppm is predicted for the proton H13 of the methine group and at 1.80ppm due to the methylene hydrogen atoms H14 and H15. Table 5 gives the

13

C NMR predicted chemical shift values obtained by RHF, B3PW91,

B3LYP and ChemDraw Ultra 10.0 software program along with the assignment. The carbon

atom C1 appearing at very higher chemical shift value 172.57 ppm in HF, 167.50 ppm in B3PW91, 170.3 ppm in B3LYP and 173.4 ppm in ChemDraw Ultra due to the negative charge of oxygen atom(O5). The carbon atom C1 is electropositive and possess more positive charges than the other carbon atoms, and hence shielding is very small and appears up field. The theoretical and ChemDraw Ultra methods revealed that the more electron rich atoms are C3, C4 and C10 and they are highly shielded atoms and hence appear at downfield (lower chemical shift). In this study a good correlation between atomic charges and chemical shift was made. It is concluded that the predicted chemical shift values by the theoretical methods, slightly deviates from the experimental value due to the fact that theoretical calculations being carried out in the isolated gas phase. UV spectral analysis The chemical structure of S2OPB consists of the conjugated system with single and double bonds of heterocyclic rings. All these structures allow σ- σ* and π- π* transitions in the UV-Vis region with high extinction coefficients. Electronic transition energies and oscillator strength (f), the wavelength of absorption (λ) and spectral assignments were calculated employing Time Dependent method using B3WP91 and B3LYP for which the optimized geometry obtained from DFT calculations were used. The results of the theoretical calculations of electronic transition energies along with the measured UV-Vis data are presented in the Table 6. The UV spectrum of S2OPB is presented in Fig. 9. The present experiment revealed three absorption bands at 226, 216 and 200 nm in the UV region, which implies the transition between σ and π electrons. However the theoretically calculated values are slightly higher than the observed electronic absorption bands of S2OPB.

Global quantities The popular

qualitative chemical concepts like hardness (η),

softness (S),

electronegativity (χ) and electrophilicity index (ω) can be defined using the energy gap between HOMO and LUMO energy levels [21]. Density functional theory [22] has been found to be successful in providing theoretical concepts mentioned above. Hence, in the present study DFT based B3WP91 and B3LYP methods have been used to determine various chemical parameters. Theoretically, the Ionization potential (I) is defined as the amount of energy required to remove an electron from a molecule I= -E HOMO Electron affinity (A) is defined as the energy released when a proton is added to a system. A= -ELUMO The ionization potential and electron affinity by B3WP91/6-31G(d,p) and B3LYP/6-31G(d,p) for S2OPB is 6.3360 eV, 6.2948 eV and -0.2718 eV, 0.3517 eV respectively. The electronegativity is the measure of the power of an atom or group of atoms to attract electrons towards itself [23]. χ = (I+A)/2 Chemical hardness (η) measures the resistance of an atom to a charge transfer [24]. η = (I- A)/2

Chemical softness (S) is the measure of the capacity of an atom or group of atoms to receive electrons [25]. S = 1/ η According to Parr et al [26] the relationship between chemical potential with the first derivative of the energy (E) with respect to the number of electrons (N) in the external potential of the system v(r), therefore the electronegativity χ can also be expressed as

µ = v(r) = - χ Similarly, hardness (η) is defined as the second derivative of the energy E with respect to N as v(r) measures the stability and reactivity of the molecule η2E/ dN2) v(r) The electrophilicity is a descriptor of reactivity that allows a quantitative classification of the global electrophilic nature of a molecule within a relative scale. The electrophilicity index (ω) is defined as ω = µ2/2 η Using the above equations the hardness (η), softness (S) electronegativity (χ) and electrophilicity index (ω) were calculated for S2OPB and the respective values are given in Table 7. The usefulness of these quantities has been recently demonstrated in understanding the toxicity of various pollutants in terms of their reactivity and site selectivity [27-29]. The calculated value of electrophilicity index describes the biological activity. Local reactivity descriptors The most relevant local descriptor of reactivity is the Fukui function. Yang and Parr [30] proposed a finite difference to calculate Fukui function indices. In a molecular system, fk+ measures the change in density when the molecule gains electrons and it corresponds to reactivity with respect to nucleophilic attack. Whereas, fk - corresponds to reactivity with respect to electrophilic attack when the molecule losses electrons. In addition to fukui function the local softness (Sk+, Sk-, Sk0) is also used to describe the reactivity of the molecular system. Fukui function and local softness for selected atomic sites in S2OPB have been listed in the Table 8. From the values reported in the Table 8, the highest nucleophilic attack is on C9. The other nucleophilic attack order was found to be C11 > C4 > C3 > C2 > C10. The sites for electrophilic

attack were C4, C9, and C10. The radial attack was on C11, C9 and C4. Sk+, Sk- and Sk0 predicts the most nucleophilic and electrophilic and radial attack in a molecule is the one which has the Sk+,-/0 value, in turn is the softest region in a molecule. Thermodynamic properties Several calculated thermodynamic parameters such as Rotational constants, Enthalpy, Gibbs free energy and dipole moment at room temperature are presented in Table 9. Scale factors have been recommended for an accurate prediction in determining the zero- point

vibrational

energies and the entropy S [31]. The biggest value ZPVE of S2OPB is 150.503kcal/mol obtained by HF method whereas the smallest value is 140.575 kcal/mol obtained by B3LYP method. The dipole moment of the molecule was also calculated by HF, B3PW91 and B3LYP methods with 6-31G (d, p) basis set. Dipole moment reflects the molecular charge distribution and is given as a vector in three dimensions. Therefore, it can be used as a descriptor to depict the charge movement across the molecule depending upon the centers of positive and negative charges. Dipole moments are strictly determined for neutral molecules. For charged systems, its value depends on the choice of origin and molecular orientation. As a result of calculations of different methods the highest dipole moments were observed for HF whereas the smallest one was observed for B3LYP in S2OPB. The study of the variation of thermodynamic parameters with temperature provides information for the further study on the S2OPB and also can be used to compute the other thermodynamic energies according to the relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics. The standard thermodynamic functions: heat capacity, entropy and enthalpy at various temperature for S2OPB are listed in the Table 10. The correlation equations between entropy, heat capacity and enthalpy

changes and temperatures are built in by quadratic formulas and are as follows and the correlation graphs of these parameters are presented in the Fig. 10. S0m = 237.5889 + 0.79517T – 1.7428x10-4T2 C0p = 19.70089 + 0.69704T – 2.51826x10-4T2 H0m = – 6.55878 + 0.0815T – 2.1284x10-4T2 The fitting factors (R2) for entropy, heat capacity and enthalpy are 0.9999, 0.9989, and 0.9996 respectively.

Conclusion The geometry of S2OPB was optimized by HF, DFT based B3WP91 and B3LYP methods. The molecular structure, vibrational frequencies, HOMO and LUMO energy gap, 1H-NMR and 13

C-NMR, nucleophilic and electrophilic attacking sited in S2OPB has been studied. On the basis

of the calculated and experimental results, assignment of the fundamental frequencies was examined. The available experiment results were compared with theoretical data. Theoretical 1

H-NMR and

13

C NMR chemical shift values were reported and compared with experimental

data, showing a good agreement both for

1

Hand

13

C. Thus, the present investigation provides

vibrational assignments, structural information and thermodynamic properties of the compound which may be useful to upgrade further knowledge on S2OPB. Acknowledgement One of the authors Mrs. T. Ramya is thankful to SAIF, IIT, Madras, for providing structural analysis of the title compound. My Sincere thanks to all the other authors for their support in all aspects.

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Fig. 1. Atom numbering of S2OPB

Fig. 2. FTIR spectrum of S2OPB (Experimental, HF, B3PW91, B3LYP/6-31G(d,p))

Atoms

Fig. 3. FT Raman spectrum of S2OPB

H26 H25 H24 H23 H22 H21 H20 H19 H18 H17 H16 H15 H14 H13 O12 C11 C10 C9 C8 N7 N6 O5 C4 C3 C2 C1

B3PW91/6-31G(d,p) B3LYP/6-31G(d,p) HF/6-31G(d,p)

-1.0

-0.5

0.0

0.5

1.0

Charges

Fig. 4. Graphical representation of Mulliken and Natural charge distribution of S2OPB

Fig. 5. Homo and Lumo energy structure of S2OPB

Fig. 6. Two dimensional Contour map of S2OPB

Fig. 7. 1H NMR spectrum of S2OPB (Experimental,HF,B3PW91,B3LYP/6-31G(d,p))

Fig. 8.

13

C NMR spectrum of S2OPB (Experimental,HF,B3PW91,B3LYP/6-31G(d,p))

Fig. 9. UV Spectrum of S2OPB

900 800

Thermodynamic Parameter

700

Entropy(S)

600 500

Heat Capacity(Cp)

400 300

Enthalpy(H) 200 100 0 200

400

600

800

1000

Temperature(K)

Fig. 10. Thermodynamic functions graph of S2OPB

Table 1. Selected bond lengths (A0) of S2OPB Parameters C1-C2 C1-O5 C1-N6 C2-C3 C2-C7 C2-H13 C3-C4 C3-H14 C4-H15 C4-H16 C4-H17 C4-H18 N6-H19 N6-H20 N7-C8 N7-C11 C8-C9 C8-O12 C9-C10 C9-H21 C9-H22 C10-C11 C10-H23 C10-H24 C11-H25 C11-H26

HF/6-31G(d,p) 1.531 1.200 1.349 1.526 1.457 1.082 1.527 1.085 1.083 1.085 1.085 1.086 0.993 0.995 1.351 1.456 1.514 1.203 1.531 1.086 1.081 1.538 1.084 1.082 1.086 1.082

Method/basis set B3WP91/6-31G(d,p) 1.542 1.222 1.358 1.524 1.460 1.096 1.525 1.095 1.095 1.094 1.094 1.095 1.008 1.014 1.362 1.456 1.520 1.228 1.532 1.097 1.092 1.541 1.094 1.093 1.098 1.095

B3LYP/6-3G(d,p) 1.546 1.224 1.362 1.529 1.467 1.095 1.531 1.095 1.094 1.094 1.095 1.095 1.009 1.014 1.366 1.464 1.525 1.229 1.538 1.096 1.091 1.547 1.094 1.092 1.097 1.094

Exp.value 1.530 1.240 1.319 1.530 1.460 1.094 1.53 1.094 1.094 1.094 1.078 1.094 1.014 1.046 1.320 1.470 1.510 1.230 1.541 1.094 1.091 1.530 1.094 1.094 1.094 1.094

Table 2. Selected bond angles ( 0) of S2OPB

Parameters C2-C1-O5 C2-C1-N6 O5-C1-N6 C1-C2-C3 C1-C2-N7 C1-C2-H13

HF/6-31G(d,p) 122.534 114.047 123.404 112.081 107.872 108.403

Method/basis set B3WP91/6-31G(d,p) 122.901 112.813 124.276 112.098 108.220 108.076

B3LYP/6-3G(d,p) 122.773 113.095 124.120 112.063 108.066 108.261

Exp.value 121.0 114.9 125.7 112.0 107.5 109.4

C3-C2-N7 C3-C2-H13 N7-C2-H13 C2-C3-C4 C2-C3-H14 C2-C3-H15 C4-C3-H14 C4-C3-H15 H14-C3-H15 C3-C4-H16 C3-C4-H17 C3-C4-H18 H16-C4-H17 H16-C4-H18 H17-C4-H18 C1-N6-H19 C1-N6-H20 H19-N6-H20 C2-N7-C8 C2-N7-C11 C8-N7-C11 N7-C8-C9 N7-C8-O12 C9-C8-O12 C8-C9-C10 C8-C9-H21 C8-C9-H22 C10-C9-H21 C10-C9-H22 H21-C9-H22 C9-C10-C11 C9-C10-H23 C11-C10-H23 C11-C10-H23 C11-C10-H24 H23-C10-H24 N7-C11-C10 N7-C11-H25 N7-C11-H26 C10-C11-H25 C10-C11-H26

113.303 109.169 105.718 113.001 107.360 109.978 109.535 110.974 105.664 110.484 111.988 111.176 107.722 107.552 107.552 117.804 120.619 119.203 121.506 124.063 114.067 107.923 125.278 126.797 103.418 107.938 110.575 112.181 114.615 107.902 104.048 109.782 113.424 109.603 112.147 107.784 103.327 110.801 110.608 111.666 112.422

113.297 109.819 104.968 113.394 107.087 109.469 110.038 111.337 105.100 110.835 111.978 111.220 107.643 107.682 107.272 117.997 119.673 119.852 121.067 124.212 114.218 107.630 124.875 127.493 103.484 108.314 110.518 112.445 114.437 107.490 104.522 109.466 111.950 107.592 103.42 110.783 103.420 110.783 110.573 111.952 112.381

113.314 109.740 105.051 113.506 107.067 109.508 109.886 111.233 105.228 110.738 111.966 111.220 107.672 107.708 107.338 117.607 119.558 119.471 121.059 124.165 114.141 107.722 124.930 127.346 103.539 108.423 110.465 112.387 114.390 107.494 104.540 109.756 113.511 109.499 111.898 107.594 103.499 110.735 110.493 111.922 112.414

114.8 109.4 104.7 112.0 109.4 109.4 109.4 112.0 109.5 109.4 109.4 109.4 109.5 109.5 109.5 118.6 118.6 119.1 126.8 126.8 113.2 107.5 121.0 127.3 104.0 109.4 109.4 109.4 109.4 109.4 104.0 109.4 109.4 109.4 109.4 109.4 104.7 108.4 108.4 109.4 109.4

H25-C11-H26

108.010

107.742

107.783

109.5

Table 3.Calculated and Experimental wave numbers (cm-1) of S2OPB Ferquency(cm-1) Mode

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

FTIR

FT Raman

3353(m) 3179(m) 2994(w) 2990(vw) 2974(vw) 2965(w) 2939(w) 2911(w) 1710(m) 1644(s) 1489(m) 1457(m) 1440(s) 1414(s) 1383(s)

2990(vs) 2942(vs) 2911(vs) 1650(m) 1463(m) 1447(m) 1431(m) 1414(m) 1384(w)

HF/6-31G(d,p) IR Freq. Intensity (cm-1) KM/Mole 3823 3684 3177 3163 3162 3149 3148 3144 3130 3108 3107 3101 3088 3076 1899 1873 1775 1663 1624 1623 1614 1606 1592 1589 1562 1539 1508

81 59 21 36 47 20 15 42 11 27 14 14 48 29 40 40 16 8 2 32 6 1 18 8 32 2 20

B3WP91/6-31G(d,p) IR Freq. Intensity (cm-1) KM/Mole 3590 3418 3046 3035 3031 3030 3007 2996 2979 2975 2968 2967 2949 2935 1757 1772 1620 1530 1501 1495 1494 1481 1468 1456 1414 1406 1376

68 71 13 15 34 40 0.27 16 16 10 5 11 22 43 32 26 16 6 4 11 12 3 7 10 15 20 24

B3LYP/6-3G(d,p) IR Vibrational assignment Freq. Intensity (cm-1) KM/Mole 3564 3405 3030 3019 3014 3012 2992 2984 2969 2968 2962 2954 2942 2926 1739 1754 1623 1536 1508 1501 1500 1489 1476 1449 1420 1404 1378

60 63 16 18 48 36 1 17 13 9 10 12 23 43 31 25 14 4 3 6 7 2 1 10 4 25 20

ν asyNH2(99) ν symNH2(99) ν asyCH2(99) ν asyCH2(84) ν asyCH2(92)+ν asyCH3(91) ν asyCH2(97)+ν asyCH3(92) ν asyCH2(99)+ν asyCH3(97) ν symCH2(97) ν symCH2(96) ν symCH2(96) ν symCH2(99) ν symCH2(99) ν symCH3(97) ν symCH2(97) ν C=O(80) ν C=O(86) β HNH(84) β HNH(84) β HCH(84)+Ʈ HCCC(40) β HCH(73)+Ʈ HCCC(54) β HCH(73) β HCH(71) β HCH(78) ν NC(36)+Ʈ HCNC(41) β HCH(70) ν NC(48)+ν CC(60)+ β HCC(57) β HCCN(36)

28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

1330(s) 1316(m) 1293(m) 1275(s) 1230(s) 1213(w) 1168(w) 1121(m) 1082(s) 1042(m) 1011(m) 943(m) 932(s)

1338(w) 1122(s) 1090(vw) 935(m) -

1472 1466 1441 1429 1403 1375 1359 1340 1331 1283 1257 1205 1191 1176 1130 1094 1089 1023 994

19 27 42 9 87 60 14 37 10 5 2 3 3 3 2 1 3 13 10

1349 1337 1315 1310 1286 1260 1248 1230 1220 1178 1166 1123 1091 1084 1054 1029 1021 958 940

14 12 3 46 40 29 2 20 3 2 2 1 2 2 1 1 3 9 1

1351 1339 1312 1308 1288 1263 1246 1223 1221 1179 1162 1119 1089 1086 1048 1020 1010 951 930

16 10 4 39 61 29 8 32 2 3 2 2 2 2 1 2 1 8 1

47 48 49 50 51 52 53 54 55 56 57 58 59

881(s) 852(s) 812(w) 703(s) 674(vw) 636(s) 584(s) 545(s)

855(m) 705(m) 545(m)

976 945 928 892 827 785 723 683 667 621 611 571 490

2 7 8 11 3 20 12 7 19 3 20 16 15

906 874 857 820 761 737 670 656 619 582 571 531 478

1 1 3 9 3 8 3 20 6 23 1 29 19

905 870 869 854 818 762 733 666 653 619 579 570 531

1 1 3 8 4 7 4 18 8 30 1 31 20

ν NC(48) β HCC(78)+Ʈ HCCN(43) Ʈ HCNC(41)+β HCC(53) β HCC(78) β HNC(68) +Ʈ HCCN(49) β HCC(57) +β HCN(68) β HCC(57)+β HCN(68) β HCC(78) +β HCN(68)+Ʈ HCCN(37) β HCC(78) +ƮHCCN(37) β HCC(78) +β HCN(68) ν CC(19) ν NC(48)+β HNC(33) Ʈ HCCC(40) Ʈ HCCN(51) Ʈ HCCC(10)+ν CC(53) Ʈ HCCC(49)+ν CC(59) ν NC(25)+ ν CC(54) ν CC(53) ν CC(59)+β CNC(33) +β CCN(33) Ʈ CNCC(57) +β HCC(33) +Ʈ HCNC(32) ν NC(36)+ ν CC(60) γ OCNC(58) +Ʈ HCCC(54) γ OCNC(58) +Ʈ HCCN(43) γ OCNC(58)+Ʈ HCCC(54) ν NC(20) γ OCNC(47)+β CCN(33) γ OCNC(47) β OCN(63) β OCC(67) γ OCNC(47)+ Ʈ HCCN(47)+β CCC(13) β OCC(67) Ʈ HNCC(85)

60 468(m) 452 0.2 436 33 435 19 Ʈ HNCC(51) +β OCC(67) 61 349(m) 387 7 362 0.18 361 0.2 ν CC(60) +β OCN(63)+ β CCC(58) 62 332 9 307 5 307 6 γ CNCC(37) +β OCC(67) 63 317 4 296 7 296 7 γ CCCN(66) +β CCN(67) 64 261 2 242 3 242 3 ƮHCCC(40) +β CNC(59) 65 181(vs) 187 1 176 5 176 5 γ CNCC(37) +β CNC(59) 66 181 9 166 7 166 9 Ʈ CNCC(57) +β CCC(58) 67 171 1 162 2 162 0.1 Ʈ CNCC(57) +β CCC(45) 68 164 2 146 1 145 1 ƮCCCN(53) +ƮCCCN(37) 69 123(s) 120 0.6 111 0.19 111 0.2 ƮCCCN(53) 70 76(vs) 84 0.3 87 0.63 87 0.7 γ CCCN(66) +Ʈ NCCC(77) 71 65 8 65 5 65 5 Ʈ NCCC(77) +Ʈ CCNC(53) 72 54 5 47 4 50 5 γ CCCN(66) +Ʈ NCCC(77) vw- very weak; w- weak; m- medium; s- strong. ν asy- asymmetric stretching; ν sym- symmetric stretching; β-In plane bending; Ʈ- out of plane bending; γ -torsion.

Table 4. Mulliken and Natural Atomic charges of S2OPB Mulliken population analysis Parameter

HF/ 6-31G(d,p)

B3WP91/ 6-31G(d,p)

B3LYP/ 6-3G(d,p)

Natural population analysis HF/ 6-31G(d,p)

B3WP91/ 6-31G(d,p)

B3LYP/ 6-3G(d,p)

C1

0.7545

0.5960

0.5770

0.8421

0.6790

0.6834

C2

-0.0133

-0.0706

-0.0148

-0.1071

-0.1592

-0.1463

C3

-0.2172

-0.2428

-0.1806

-0.4498

-0.4972

-0.4777

C4

-0.0088

-0.3963

-0.3268

-0.6487

-0.7133

-0.6875

O5

-0.6124

-0.519

-0.5154

-0.7369

-0.6234

-0.6255

N6

-0.7666

-0.6531

-0.6132

-0.9503

-0.8777

-0.8701

N7

-0.7107

-0.4571

-0.4428

-0.5872

-0.4739

-0.4749

C8

0.7699

0.5998

0.5813

0.8693

0.7012

0.7045

C9

-0.3156

-0.3305

-0.2661

-0.5294

-0.5681

-0.5458

C10

-0.2771

-0.296

-0.2338

-0.4531

-0.4958

-0.4772

C11

0.0209

-0.0705

-0.0266

-0.2074

-0.2783

-0.2611

O12

-0.6455

-0.5513

-0.5459

-0.7613

-0.6505

-0.6524

H13

0.1801

0.1660

0.1312

0.2608

0.2796

0.2700

H14

0.1370

0.1490

0.1166

0.2441

0.2684

0.2584

H15

0.1388

0.1451

0.1175

0.238

0.2586

0.249

H16

0.1218

0.1351

0.1086

0.2282

0.2501

0.2413

H17

0.1124

0.1281

0.1049

0.2144

0.2358

0.2268

H18

0.1182

0.1352

0.1100

0.2201

0.2425

0.2335

H19

0.3127

0.2894

0.2683

0.4278

0.4247

0.4179

H20

0.3399

0.3145

0.2948

0.4515

0.4409

0.4355

H21

0.1584

0.1648

0.1353

0.2519

0.2699

0.2601

H22

0.1630

0.1635

0.1331

0.257

0.2746

0.2653

H23

0.1439

0.1547

0.1251

0.2348

0.2564

0.2468

H24

0.1386

0.1431

0.1129

0.2399

0.2606

0.2515

H25

0.1275

0.1387

0.1124

0.2135

0.2363

0.2275

H26

0.1590

0.1639

0.1369

0.2373

0.2586

0.2497

Table 5. The calculated 13C and 1H NMR chemical shifts of S2OPB 13

1

C Chemical shift

H Chemical shift

Atom numbe r

631G(d,p)

B3PW91/6-

B3LYP/

31G(d,p)

6-31G(d,p)

Chem. Ultra

HF/

Atom number

HF/

B3PW91/

B3LYP/6

6-31G(d,p)

6-31G(d,p)

-31G(d,p)

Chem. Ultra

Exp

1

172.57

167.50

169.66

173.4

172.45

13

4.45

5.10

5.02

4.53

4.46

2

49.35

61.99

64.91

68.1

43.89

14

1.99

2.45

2.39

2.18

1.9

3

17.99

27.81

31.35

30.6

18.18

15

2.46

2.87

2.82

2.18

2.03

4

10.92

18.01

21.00

17.3

10.53

16

1.65

1.9

1.89

1.91

1.91

8

179.37

172.42

174.81

178.2

176.03

17

1.36

1.70

1.66

1.91

1.70

9

27.68

36.74

39.61

30.6

21.13

18

1.37

1.69

1.65

1.91

1.68

10

17.45

26.86

29.94

22.8

18.18

19

4.70

4.91

4.76

4.53

4.48

11

37.20

48.61

51.37

45.7

31.10

20

6.92

7.22

7.09

7.16

6.49

21

2.77

3.25

3.17

3.29

2.47

22

2.65

2.92

2.83

2.18

2.47

23

2.27

2.74

2.67

2.18

2.39

24

2.30

2.70

2.63

1.80

2.35

25 26

3.68 3.73

4.32 4.30

4.27 4.26

4.53 4.53

4.50 4.48

Exp

Table 6. Assignment of observed electronic transitions of S2OPB

S. No

B3WP91/6-31G(d,p) λ calc Energy

B3LYP/6-3G(d,p) λ calc Energy

(nm)

(nm) 231

231

(eV) 5.352

f 0.0164

(eV) 5.356

f 0.0158

1

2

3

State Transitions H→ L H→ L+1 H+3 → L H+3 → L+1

218

5.671

0.0011

219

5.647

0.001

H→ L H→ L+1

196

6.302

0.0647

197

6.291

0.0636

H→ L H+2→ L-1 H+2→ L+1 H→ L+5

λ Expt. (nm)

226

216

200

Table 7. Comparison of HOMO, LUMO, energy gaps and related global quantities of S2OPB

Energy values and

E HOMO(eV)

B3WP91/ 6-31G(d,p) -6.336

B3LYP/ 6-3G(d,p) -6.2948

E LUMO(eV)

0.2718

-0.3517

E HOMO- LUMO gap(eV)

6.6078

-5.9431

Ionization potential I (eV)

6.336

6.2948

Electron affinity A(eV)

-0.2718

0.3517

Electronegativity( χ )

3.0321

3.3232

Chemical hardness(η )

3.3039

2.9715

Softness(S)

0.3026

0.3365

Chemical potential ( µ )

-3.0321

-3.3232

Electrophilicity index( ω)

4.5968

5.5218

global quantities

Table 8. Condensed Fukui functions and local softness of S2OPB Atom

fk+

fk -

fk0

Sfk+

Sfk -

Sfk0

C1

-0.11901

0.00505

-0.11396

-0.04004

0.00169

-0.03834

C2

0.00669

-0.01076

-0.00407

0.00225

-0.00362

-0.00136

C3

0.00915

0.00743

0.01658

0.00307

0.0025

0.00557

C4

0.01024

0.01007

0.02031

0.00344

0.00338

0.00683

O5

-0.1103

-0.24077

-0.35107

-0.03711

-0.088

-0.11813

N6

-0.04256

-0.05828

-0.10084

-0.01432

-0.01961

-0.03393

N7

-0.03505

-0.19152

-0.22657

-0.01179

-0.06444

-0.07624

C8

-0.20168

0.00283

-0.19885

-0.06786

0.00095

-0.06691

C9

0.02263

0.00901

0.03164

0.00761

0.00303

0.01065

C10

0.00529

0.00814

0.01343

0.00178

0.00273

0.00451

C11

0.00925

0.02386

0.03311

0.00311

0.00802

0.01114

O12

-0.12492

-0.14199

-0.26691

-0.04203

-0.04777

-0.08981

H13

-0.03048

-0.04502

-0.0755

-0.01025

-0.01514

-0.0254

H14

-0.04947

-0.02619

-0.04961

-0.01664

-0.00881

-0.01669

H15

-0.0148

-0.01374

-0.02854

-0.00498

-0.00462

-0.0096

H16

-0.03106

-0.03559

-0.06665

-0.01045

-0.01197

-0.02242

H17

0.00123

-0.0022

-0.00097

-0.00041

-0.00074

-0.00032

H18

-0.01353

-0.01835

-0.03188

-0.00456

-0.00617

-0.01072

H19

-0.04092

-0.04102

-0.08194

-0.01376

-0.0138

-0.02757

H20

-0.01389

-0.01897

-0.03286

-0.00467

-0.00638

-0.01105

H21

-0.07902

-0.0345

-0.11358

-0.02659

-0.0116

-0.03819

H22

-0.05822

-0.03506

-0.09328

-0.01959

-0.01179

-0.03138

H23

-0.02291

-0.02205

-0.04496

-0.0077

-0.00741

-0.01507

H24

-0.04453

-0.03383

-0.07836

-0.01498

-0.01138

-0.02636

H25

-0.03579

-0.05993

-0.09572

-0.01204

-0.0215

-0.0322

H26

-0.02237

-0.03664

-0.05901

-0.00752

-0.01232

-0.01985

Table 9. Thermodynamic parameter of S2OPB HF/ 6-31G(d,p)

B3WP91/ 6-31G(d,p)

B3LYP/ 6-3G(d,p)

1.129 0.795 0.668 150.503

1.123 0.799 0.656 140.944

1.113 0.795 0.656 140.575

0.889 0.889 156.131 157.909 42.912 107.55 2.8516

0.889 0.889 146.954 148.731 45.761 110.096 2.8346

0.889 0.889 146.587 148.364 45.834 110.024 2.759

µx

-2.448

-2.385

-2.3

µy

1.224

1.343

1.364

µz

0.797

0.735

0.677

Parameters Rotational constants(GHz) A B C ZPVE(Kcal/mol) Energy(Kcal/mol) Translational Rotational Vibrational Total Heat capacity(Kcal/mol-Kelvin) Entropy(Cal/mol-Kelvin) Dipole moment (Debye)

Table 10. Thermodynamic parameter of S2OPB at different temperatures

Temperature(K)

100 200 298.15 300 400 500 600 700

Entropy(S0 m) (J/mol K)

311.68 392.78 460.75 461.99 527.64 590.76 650.92 707.82

Heat Capacity (C0pm) (J/mol K)

94.47 145.23 199.78 200.85 257.74 308.57 351.29 386.8

Enthalpy (H0 m) (KJ/mol )

6.19 18.17 35.06 35.43 58.39 86.77 119.83 156.79

800 900 1000

761.47 812.03 859.71

416.56 441.76 463.29

197 239.95 285.23

Graphical Abstract

HIGHLIGHTS

 The optimized geometry and vibrational assignments with PED were computed using DFT method.  The HOMO, LUMO energy gap were theoretically predicted.  Natural population analysis of the molecule were studied.  A thermodynamics properties of the title compound was calculated at the different temperatures.

Molecular structure, spectroscopic characterization of (S)-2-Oxopyrrolidin-1-yl Butanamide and ab initio, DFT based quantum chemical calculations.

The experimental and theoretical spectra of (S)-2-Oxopyrrolidin-1-yl Butanamide (S2OPB) were studied. FT-IR and FT-Raman spectra of S2OPB in the solid...
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