Accepted Manuscript Molecular structure and spectroscopic characterization of Carbamazepine with experimental techniques and DFT quantum chemical calculations M. Suhasini, E. Sailatha, S. Gunasekaran, G.R. Ramkumaar PII: DOI: Reference:

S1386-1425(15)00080-3 http://dx.doi.org/10.1016/j.saa.2015.01.059 SAA 13227

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

24 August 2014 4 November 2014 25 January 2015

Please cite this article as: M. Suhasini, E. Sailatha, S. Gunasekaran, G.R. Ramkumaar, Molecular structure and spectroscopic characterization of Carbamazepine with experimental techniques and DFT quantum chemical calculations, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/ 10.1016/j.saa.2015.01.059

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Molecular structure and spectroscopic characterization of Carbamazepine with experimental techniques and DFT quantum chemical calculations M. Suhasinia, E. Sailathaa, S. Gunasekaranb, G.R. Ramkumaarc*

a

PG and Research Department of Physics, Pachaiyappa’s College, Chennai 600030, 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 in Anna Nagar East, Chennai 600102, TN, India *Corresponding Author (email: [email protected]) Tel.: +91 9884351008 Abstract A systematic vibrational spectroscopic assignment and analysis of carbamazepine has been carried out by using FT-IR, FT-Raman and UV spectral data. The vibrational analysis were aided by electronic structure calculations – ab initio (RHF) and hybrid Density Functional methods (B3LYP) performed with standard basis set 6-31G(d,p). Molecular equilibrium geometries, electronic energies, natural bond order analysis, harmonic vibrational frequencies and IR intensities have been computed. A detailed interpretation of the vibrational spectra of the molecule has been made on the basis of the calculated Potential Energy Distribution (PED) by VEDA program. UV–visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and λmax were determined by HF/6-311++G(d,p)

Time-Dependent method. The thermodynamic functions of the title

molecule were also performed using the RHF and DFT methods. The restricted Hartree-Fock and density functional theory-based nuclear magnetic resonance (NMR) calculation

1

procedure was also performed, and it was used for assigning the

13

C and 1H NMR chemical

shifts of carbamazepine. Keywords : carbamazepine; UV; vibrational spectra; RHF; DFT.

Introduction Carbamazepine is an anticonvulsant drug. It is white crystalline powder, almost odourless, exhibits polymorphism. The systematic IUPAC name of Carbamazepine is 5Hdibenz (b,f) azepine-5-carboxamide. Its molecular formula is C15H12N2O. The molecular weight of Carbamazepine is 236.27[1]. Carbamazepine is used alone or in combination with other medications to control certain types of seizures in patients with epilepsy. It is also used to treat trigeminal neuralgia (a condition that causes facial nerve pain). Carbamazepine extended-release capsules (Equetro brand only) are used to treat episodes of mania or mixed episodes (symptoms of mania and depression that happen at the same time) in patients with bipolar first disorder (manic-depressive disorder; a disease that causes episodes of depression, episodes of mania, and other abnormal moods). Carbamazepine is in a class of medication called anticonvulsants. It works by reducing abnormal electrical activity in the brain. Thus, an attempt has been made in the present work to compute and compare with ground

state optimised

molecular

geometrical parameters,

harmonic

frequencies,

thermodynamic and electronic properties using the Ab initio Restricted Hartree-Fock (RHF) and Becke’s three parameter exact exchange functional (B3) combined with gradient corrected correlation functional of Lee, Yang and Parr (LYP) methods with the 6-31G(d,p) basis set. These methods predict substantial optimised molecular structure and wavenumbers for the vibrational modes with moderate computational effect. The present vibrational spectroscopic studies of Carbamazepine not only help for the proper assignments of the

2

observed and computed frequencies but also offer a comprehensive picture on the molecular dynamics and electronic properties. Experimental: The solid phase FT-IR spectrum was recorded in the region 4000-400 cm-1 in evacuation mode on Nexus 670 DTGS using KBr pellet technique with 4.0 cm-1 resolution. The FT-Raman spectrum was recorded using 1064 nm line of Nd: YAG laser as excitation wavelength in the region 4000-50 cm-1 on Bruker IFS 66V spectrometer equipped with FRA 106 Raman module was used as an accessory. The UV–vis spectral measurements were carried out in the range 200–600 nm using a Varian cary 5E-UV-NIR spectrophotometer. 1H NMR,

13

C NMR spectra were recorded on a Bruker Advance DPX 300 MHz and 2D homo

cosy NMR spectra were recorded on a Bruker Advance DPX 500 MHz ultra-shield FT-NMR spectrophotometer in DMSO-d6 with TMS as internal standard chemical shifts are expressed in (б units ppm) SAIF IIT Madras. The spectral measurements were carried out at sophisticated instrumentation Analysis Facility, IIT, Madras, India. Computational details To provide complete information regarding the structural characteristics and the fundamental vibrational modes of Carbamazepine the restricted Hartree-Fock and DFTB3LYP correlation functional calculations have been carried out. The calculations of geometrical parameters in the ground state were performed using the Gaussian 03 [2] programs, invoking gradient geometry optimization [3] on Intel core i3/2.93 GHZ processor. The geometry optimization was carried out using the initial geometry generated from standard geometrical parameters at restricted Hartree-Fock level, and B3LYP methods adopting the 6-31G(d,p) basis set to characterize all stationary points as minima. The optimized structural parameters of the compound Carbamazepine were used for harmonic vibrational frequency calculations resulting in IR and Raman frequencies together with

3

intensities. In DFT method, Becke’s three parameter exchange-functional (B3) [4,5] combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) [6] by implementing the split-valence polarized 6-31G(d,p) basis set [7,8] has been utilized for the computation of molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The 1H and

13

C nuclear magnetic

resonance (NMR) chemical shifts of the title compound were calculated using the keyword NMR in the RHF and DFT calculation at the B3LYP level with 6-31G(d,p) basis set. Results and discussion Molecular geometry The molecular structure of Carbamazepine belongs to C1 point group symmetry. All vibrations are active in both IR and Raman. The optimized molecular structure of Carbamazepine is shown in Fig. 1. The optimized geometrical parameters such as bond lengths and bond angles obtained by DFT and restricted HF methods for the molecule are presented in Table 1. From the calculated values, we can find that most of the optimized bond length and bond angles are slightly varied with experimental data [9]. The difference is due to fact that theoretical calculation are performed on isolated molecules in the gaseous phase whereas the experimental results belongs to the molecules in the solid phase [10, 11]. Table 1 also gives the geometry difference between experimental values and the calculated values obtained from B3LYP method. It is to be noticed that there is an appreciable bond angle difference and insignificant bond length difference is observed which is mentioned in Table 1. Frontier molecular orbitals (FMOs) The most important orbitals in molecules are the frontier molecular orbitals, called highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). These orbitals determine the way the molecule interacts with other species. The

4

frontier orbital gap helps to characterize the chemical reactivity and kinetic stability of the molecule. A molecule with a small frontier orbital gap is more polarizable and is generally associated with a high chemical reactivity, low kinetic stability and is also termed as soft molecule [12–14]. The low values of frontier orbital gap in Carbamazepine make it more reactive and less stable. The HOMO is the orbital that primarily acts as an electron donor and the LUMO is the orbital that largely acts as the electron acceptor. The energies of four important molecular orbitals of Carbamazepine: the highest and second highest occupied MO’s (HOMO and HOMO−1), the lowest and the second lowest unoccupied MO’s (LUMO and LUMO+1) were calculated and are presented in Table 2. The lowest singlet→singlet spin-allowed excited states of Carbamazepine were taken into account for the TD-DFT calculation in order to investigate the properties of electronic absorption. The experimental λmax values are obtained from the UV- Visible spectra recorded in ethanol. The calculations were also performed with ethanol solvent effect. The calculated absorption wavelengths (λmax), oscillator strength, excitation energies and the experimental wavelengths are also given in Table 3. The energy gap between HOMO and LUMO is a critical parameter in determining molecular electrical transport properties [15]. In the electronic absorption spectrum of Carbamazepine, there are three absorption bands with a maximum 285.36 nm. The strong absorption band 213.84 nm is caused by the π →π* and the other moderately intense bands are due to n→π* and π→π* transitions. The π→π* transitions are expected to occur relatively at lower wavelength, due to the consequence of the extended aromaticity of the benzene ring. The 3D plots of the frontier orbitals HOMO and LUMO for Carbamazepine are shown in Fig. 2. The positive phase is red and the negative one is green. It can be seen from the figure that, the HOMO levels are spread over the entire molecule. The LUMO in Carbamazepine is found to spread over the entire molecule except N-amide group. The energy gap of HOMO–LUMO explains the eventual charge transfer interaction within the

5

molecule, which influences the biological activity of the molecule. As the energy gap between the LUMO and HOMO decreases, it is easier for the electrons of the HOMO to be excited. The higher the energy of HOMO, the easier it is for HOMO to donate electrons whereas it is easier for LUMO to accept electrons when the energy of LUMO is low. The energy values of HOMO and LUMO levels for Carbamazepine are computed to be -0.3030 a.u. and 0.0336 a.u., respectively, and the energy difference is -0.3366 a.u. Chemical reactivity Global reactivity descriptors The energies of frontier molecular orbitals (EHOMO, ELUMO), energy band gap (EHOMO ELUMO), electronegativity (χ), chemical potential (µ), global hardness (η), global softness (S) and global electrophilicity index (ω) [16–18] of Carbamazepine are listed in Table 3. On the basis of EHOMO and ELUMO, these are calculated by using the below equations. 1 2

χ = − ( +  ) 1  = −χ = ( +  ) 2 1  = (  −  ) 2 =

1 2

=

 2

Electrophilicity index is one of the important quantum chemical descriptors in describing toxicity or biological activities of the molecules in the context of development of Quantitative Structure Activity Relationship (QSAR) parlance. Quantitative Structure Activity Relationship (QSAR) methodology is one of the most powerful tool for describing the

6

relationships between biological activity and the physicochemical characteristics of molecules. The molecular descriptor is the final result of a logic and mathematical procedure which transforms chemical information encoded within a symbolic representation of a molecule into a useful number or the result of some standardized experiment. Many of the descriptors are based directly on the results of quantum–mechanical calculations or can be derived from the electronic wave function or electrostatic field of the molecule [19]. Since the electrophilicity index is a chemical reactivity descriptor and it has been used as appropriate descriptor of QSAR study. Recently the electrophilicity index has been used as a possible descriptor of biological activity confirming the fact that the electrophilicity properly quantifies the biological activity. A previous QSAR study made with Multiple Linear Regression and found that the HOMO and LUMO energies are the most important descriptors for describing the drug-receptor interaction of the molecules [20]. It has found that electrophilicity is sufficient enough to describe the toxicity of the molecule. The usefulness of this new reactivity quantity has recently demonstrated in understanding the toxicity of various pollutants in terms of their reactivity and site selectivity [21]. The computed electrophilicity index of Carbamazepine describes the biological activity of drug receptor interaction. Natural population analysis The calculation of effective atomic charges plays an important role in the application of quantum mechanical calculations to molecular systems. Our interest here is in the comparison of different methods (RHF and DFT) to describe the electron distribution in Carbamazepine as broadly as possible, and to assess the sensitivity of the calculated charges to change the choice of quantum chemical method. The calculated natural atomic charge values from the natural population analysis (NPA) and Mulliken population analysis (MPA) procedures using the RHF and DFT methods are listed in Table 4. The NPA from the natural bonding orbital

7

(NBO) method is better than the MPA scheme. Table 4 compares the atomic charge site of Carbamazepine from both MPA and NPA methods. The NPA of Carbamazepine shows that the presence of two nitrogen atoms (N1 = -0.525 (RHF) and -0.425 (DFT), N18 = −0.831 (RHF) and −0.742 (DFT), and O17 = −0.77 (RHF) and −0.656 (DFT)) imposes large positive charges on the carbon atoms (C2 = 0.196 (RHF) and 0.15 (DFT), C7 = 0.165 (RHF) and 0.142 (DFT) and C16=0.994 (RHF) and 0.809 (DFT)). However, the nitrogen atoms N1, N18 and oxygen atom O17 possess large negative charges, resulting in the positive charges on the carbon atoms C2, C7, and C16. Moreover, there is no difference in charge distribution observed on all hydrogen atoms except the H30 hydrogen atom (H30 = 0.407 in RHF and 0.401 in DFT). The large positive charge on H30 is due to the large negative charge accumulated on the N18 atom. Predication of hyperpolarizability Density functional theory has been used as an effective method to investigate the organic NLO materials. Recent research works have illustrated that the organic non-linear optical materials are having high optical non-linearity than inorganic materials [22]. Recently Carbamazepine has identified as new organic material for NLO applications [23]. The first order hyperpolarizability (βtotal) of the title compound Carbamazepine along with related properties (µ, (α) and ∆α) are calculated by using DFT-B3LYP method with 6-31(d,p) basis set. Based on the finite-field approach, the energy of a system is a function of the electric field. First order hyperpolarizability is a third rank tensor that can be described by a 3 x 3 x 3 array. The 27 components of the 3D matrix can be reduced to 10 components due to the Kleinman symmetry [24]. It can be given in the lower tetrahedral format. The components of βtotal are defined as the coefficients in the Taylor series expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion becomes:

8

E = E0 – µ αFα – 1/2ααβFαFα – 1/6βαβγ FαFβFγ + . . . where E0 is the energy of unperturbed molecule, Fα the field at the origin, µ α, ααβ, and βαβγ are the components of dipole moment, polarizability and the first order hyperpolarizabilities, respectively. The total static dipole moment (µ), the mean dipole polarizability (α), the anisotropy of the polarizability (∆α) and the total first order hyperpolarizability βtotal, using x, y, z components they are defined as  = [ +  +  ]/ =

 

!! "

# 



 / ∆ = 2%/ [& −  ' + & −  ' + ( −  ) + 6 ]

)* = () + ) + ) )/ and ) = ) + ) + ) ) = ) + ) + ) ) = ) + ) + ) In the present work, the calculated dipole moment, polarizability and first order hyperpolarizability values are obtained from B3LYP/6-31G(d,p) method and listed in Table 5. The total molecular dipole moment of Carbamazepine from B3LYP with 6-31G(d,p) basis set is 1.3927D which is nearer to the value for urea (µ = 1.3732 D). Urea is one of the prototypical molecule used in the study of the NLO properties of molecular systems. Therefore it has been used frequently as a threshold value for comparative purposes. Theoretically, the first-order hyperpolarizability of the title compound is of 21 times magnitude of urea. This result indicates the nonlinearity of the Carbamazepine molecule. 9

Vibrational assignment The experimental and simulated FT-IR and FT-Raman vibrational spectra were shown in Figs. 3 and 4. Since the calculated vibrational wavenumbers were known to be higher than the experimental ones, they were scaled down by the wavenumber linear scaling procedure of Yoshida et al. [25] using the following expression: ν ob s = (1.0087−0.0000163ν c a l c ) ν c a l c The above expression is used by Soni Mishra et al [26], which really scaled the theoretical value to the observed values. Vibrational spectral assignments have been carried on the recorded FT-IR and FT-Raman spectra based on the theoretically predicted wavenumbers by RHF and B3LYP with the 6-31G(d,p) basis set along with their PED values and are presented in Table 6. Comparison of the frequencies calculated at RHF and DFT-B3LYP with experimental values (Table 6) reveals the overestimation of the calculated vibrational modes due to anharmonicity in real system which was neglected. Inclusion of electron correlation in DFT to a certain extent makes the frequency values smaller in comparison with the RHF frequency data. According to the theoretical calculations, Carbamazepine has a non-planar structure of C1 point group symmetry. The molecule has 30 atoms and 84 normal modes of vibration active in both IR and Raman. NH2 group vibrations The NH2 group has two (N-H) stretching vibrations, one being symmetric and other asymmetric. The frequency of asymmetric vibration is higher than that of symmetric one. It has frequency range of 3300 cm-1 to 3700 cm-1. In addition, NH2 group has scissoring, rocking, wagging and torsion modes. The NH2 scissoring mode has been suggested to lie in the region 1590 cm-1 to 1650 cm-1 in benzene derivatives containing an NH2 group [1]. Hence, in the present investigation, the NH2 stretching vibrations have been found at 3465 cm−1 in IR, which are further supported by the RHF and DFT-B3LYP method.

10

C=C stretching vibrations Benzene has two doubly degenerate modes and two non-degenerate modes of vibrations due to stretching of C=C bonds. The C=C stretching vibrations occur in the region 1625-1430 cm1

[1]. In the present work, the FT-IR band observed at 1594 cm-1 has been assigned to C=C

stretching vibrations. Also the corresponding Raman band is identified at 1601 cm-1. The C=C vibrations calculated experimentally are in good agreement with the theoretically attained by DFT and RHF methods. C-N vibrations The identification of C-N stretching frequency is a very difficult task, since the mixing of bands is possible in this region. Hence the FT-IR bands observed at 1383, 1307, 1245,1115 and 1039 cm-1 and the Raman bands at 1309,1250, 1117 and 1025 cm-1 in Carbamazepine are assigned to C-N stretching vibrations. These assignments are made in accordance with the assignments proposed by Roy [27]. The C-N vibrations calculated experimentally are in good agreement with the theoretically attained by DFT and RHF methods. C-C-C bending vibrations. The C-C-C bending bands always occur below 700 cm-1. Isopropyl benzenes [28, 29] have a medium intensity absorption band in the region 545-525 cm-1. Hence, in the present investigation, the FT-IR bands observed at 705, 647 and 624 cm-1 and the Raman bands at 700, 646, 620 and 582 cm-1 are due to C-C-C bending vibrations. The calculated bands at B3LYP and RHF levels in the same region are in excellent agreement with experimental observations of both in FT-IR and FT- Raman spectra of Carbamazepine. Thermodynamic properties On the basis of vibrational analysis at B3LYP/6-31G(d,p), the standard statistical thermodynamic functions: heat capacity (C0 p:m), entropy (S0 m), and enthalpy changes (∆H0 m) for the title compound were obtained from the theoretical harmonic frequencies and listed in

11

Table 7. From Table 7, it can be observed that these thermodynamic functions are increasing with temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities increase with temperature [30, 31]. The correlation equations between heat capacities, entropies, enthalpy changes and temperature are fitted by quadratic formulas. The corresponding fitting factors (R2) for these thermodynamic properties are 0.9998, 0.9995 and 0.9996, respectively. The standard deviation is very least in the calculation of enthalpy change. The corresponding fitting equations are as follows and the correlation graphics of those shows in Fig. 5. C0p.m = 227.22259 + 0.92949 T – 1.74344 X 10-4 T2

(R2=0.9999)

S0m

(R2=0.9991)

= -11.71747 + 1.00096 T – 4.29357 X 10-4 T2

∆H0 m = -10.84161 + 0.09664 T + 2.6589 X 10-4 T2

(R2=0.9992)

All the thermodynamic data supply helpful information for the study on the Carbamazepine. They can be used to compute the other thermodynamic energies according to relationship of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics. Notice: all thermodynamic calculations were done in gas phase and they could not be used in solution. The total energy of a molecule is the sum of translational, rotational, vibrational and electronic energies, i.e., E = Et + Er + Ev + Ee. Thus, the molecular partition function is the product of the translational, rotational, vibrational, and electronic partition functions of the molecule [32]. The relations between partition functions and various thermodynamic functions were used to evaluate the latter due to translational, vibrational, and rotational degrees of freedom of molecular motions. The statistical thermochemical analysis of

12

Carbamazepine is carried out considering the molecule to be at room temperature of 298.15 K and 1 atom pressure. In the present analysis using B3LYP, the contributions due to internal rotations are not considered. The free energy of the molecule is calculated including zeropoint vibrational energy. The values of zero-point energy of the molecule were 149.330 kcal/mol by DFT method and 160.097 kcal/mol by RHF method, respectively. Microscopically, the thermal energy is the kinetic energy of a system's constituent particles, which may be atoms, molecules, electrons, or particles in plasmas. Table 8 summarizes the calculated thermodynamic parameters, namely heat capacity, entropy, rotational constants, and dipole moments of Carbamazepine. Knowledge on permanent dipole moment of a molecule provides a wealth of information to determine the exact molecular conformation. The total dipole moment of Carbamazepine in DFT-B3LYP method is the lesser side of the dipole moment value of RHF method which was observed. From Table 8, it is concluded that the variations in the entropy and zero-point vibrational energies seem to be insignificant. 13

C and 1H NMR chemical shift assignment The isotropic chemical shifts are frequently used as an aid in identification of relative

ionic species. 1H NMR and

13

C NMR spectral analyses are the important analytical

techniques used to study the structure of organic compounds and the spectra are presented in Fig. 6. Table 9 presents the predicted chemical shift values of Carbamazepine obtained by RHF and DFT along with the shielding values. In general, highly shielded electrons appear downfield and vice versa. The predicted chemical shift values by the theoretical methods, both DFT and RHF, slightly deviates from the experimental values due to the theoretical calculations being carried out in the isolated gas phase. The proton NMR spectrum of Carbamazepine showed a singlet at 6.96 ppm is due to the protons of H19 and H20 of the heterocyclic ring, which is in good agreement with the DFT & RHF theoretical prediction, 6.0, 6.2 ppm and 6.1, 6.9 ppm respectively. In the proton

13

NMR spectrum, triplets are observed at 7.44, 7.46, 7.5, 7.43 ppm for the benzene ring of the hydrogen atoms H22, H23, H26, H27 which is in good agreement with DFT and RHF theoretical values 7.4, 7.8, 8.3, 7.5 ppm and 7.5, 8.0, 8.3, 7.4 ppm respectively. In DFT and RHF methods, the hydrogens in 1-benzene and urea group (H24, H25 and H29) is predicted. It contradicts to theoretical values, but other hydrogen atoms fairly agrees with the experimental values. compound. The

13

13

C NMR spectrum gives carbon atoms environment in the title

C NMR spectrum of carbamazepine showed a peak at 157.3 ppm due to

C16 of N-amide group. The carbon atom C16 appearing at a very higher chemical shift value 153.1 ppm in DFT and 156.1 ppm in RHF methods respectively which is in good agreement with the experimental value. The peaks at 140.0 and 135.1 ppm are due to the carbon atoms (C2 and C7) of heterocyclic ring which are agreed with the theoretical chemical shift values. The peak at 128.7 and 130.5 ppm of experimental spectrum is corresponding to C15 and C8 of two benzene rings. The carbon atoms C15 and C8 resonates at 134.9, 137.9 ppm in DFT and 128.6, 135.6 ppm in RHF respectively. C15 and C8 are in good agreement with the experimental values. Similarly, the other peaks in 13C NMR spectrum at 129.6 and 127.7 ppm are due the carbon atoms C13 and C14 respectively, which agreed with the theoretical DFT and RHF chemical shift values. Thus, it is clear that calculated values by DFT and RHF are found to agree well with the experimental values. Conclusion The geometry of Carbamazepine was optimized with RHF and DFT-B3LYP methods using 6-31G(d,p) basis set. The complete molecular structural parameters and thermodynamic properties of the optimized geometry of the compound have been obtained from ab initio and DFT calculations. The atomic charges of the title molecule have been studied by both RHF and DFT methods. The vibrational FT-IR and FT-Raman spectra of the Carbamazepine are recorded and on the basis of agreement between the calculated and experimental results, the

14

assignments of all the fundamental vibrational modes of the title compound are made unambiguously based on the results of the PED output obtained from normal coordinate analysis. The energies of important MO’s, absorption wavelength (λmax), oscillator strength and excitation energies of the compound were also determined from HF/6-311++G(d,p) Time-Dependent method and compared with the experimental values. This study predicted that the molecular geometry, vibrational wave numbers and 13C and 1H NMR chemical shifts for Carbamazepine could be successfully elucidated by the B3LYP/6-31G(d,p) and RHF/631G(d,p) methods using Gaussian program. These computations are carried out with the main aim that the results will be of assistance in the quest of the experimental and theoretical evidence for the title molecule in biological activity and coordination chemistry. Acknowledgement One of the authors Mrs. M. Suhasini 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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[25] H.Yoshida, K.Takeda, J.Okamura, A. Ehara, H. Matsuura, J. Phys. Chem. A 106, (2002) 3580-3586. [26] S. Mishra, D. Chaturvedi, A. Srivastava, P. Tandon, A.P. Ayala, H.W. Siesler, Vibrational Spectrosc., 53 (2010) 112-116. [27] J.N. Roy, Indian J. Phys. B 65 (1991) 364–370. [28] S. Gunasekaran, G. Sankari, S. Ponnusamy, Spectrochim. Acta, 61 A (2005) 117-127. [29] S. Gunasekaran, S. Seshadri, S. Muthu, Indian J. of Pure & Appl. Phys., 44 (2006) 360366. [30] J. BevanOtt, J. Boerio-Goates, Calculations from Statistical Thermodynamics, Academic Press, 2000. [31] D. Sajan, L. Josepha, N. Vijayan, M. Karabacak, Spectrochim. Acta A 81 (2011) 85–98 [32] S.

Srinivasan,

Gnanaprakasam,

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18

S.

Fig. 1 Atom numbering scheme of Carbamazepine

19

Fig. 2 3D plots of HOMO and LUMO

20

Fig. 3 Experimental and Simulated FT-IR spectrum of Carbamazepine

21

Fig. 4 Experimental and Simulated FT-Raman spectrum of Carbamazepine

22

Fig. 5 Thermodynamic properties of Carbamazepine

23

Fig. 6 13C and 1H NMR spectra of Carbamazepine

24

Table 1 Geometrical parameters optimized in Carbamazepine, bond length (A°), bond angle (°). Parameter

RHF/631G(d,p)

B3LYP/631G(d,p)

Experimental Value

∆= Exp.val- DFT

N1-C2 N1-C7 N1-C16

1.425 1.426 1.381

1.431 1.432 1.402

1.438 1.434 1.38

0.007 0.002 -0.022

C2-C3

1.395

1.413

1.395

-0.018

C2-C11

1.390

1.400

1.384

-0.016

C3-C4

1.473

1.462

1.459

-0.003

C3-C8

1.397

1.409

1.402

-0.007

C4-C5

1.330

1.351

1.331

-0.02

C4-H19 C5-C6 C5-H20 C6-C7 C6-C15 C7-C12 C8-C9 C8-H21 C9-C10 C9-H22 C10-C11 C10-H23 C11-H24 C12-C13 C12-H25 C13-C14 C13-H26 C14-C15 C14-H27 C15-H28 C16-O17 C16-N18 N18-H29 N18-H30 Bond angle C2-N1-C7 C2-N1-C16

1.077 1.473 1.078 1.392 1.396 1.386 1.380 1.076 1.388 1.076 1.381 1.075 1.075 1.380 1.074 1.388 1.075 1.379 1.076 1.076 1.200 1.364 0.992 0.993

1.088 1.462 1.088 1.410 1.409 1.397 1.390 1.087 1.398 1.086 1.393 1.086 1.085 1.392 1.084 1.398 1.086 1.389 1.086 1.087 1.222 1.383 1.009 1.009

0.948 1.462 1.001 1.399 1.398 1.38 1.372 1.015 1.373 1.007 1.388 0.972 0.97 1.383 0.951 1.376 0.981 1.375 0.996 0.987 1.23 1.346 0.872 0.887

-0.14 0 -0.087 -0.011 -0.011 -0.017 -0.018 -0.072 -0.025 -0.079 -0.005 -0.114 -0.115 -0.009 -0.133 -0.022 -0.105 -0.014 -0.09 -0.1 0.008 -0.037 -0.137 -0.122

117.3 123.4

118.2 123.3

116.8 121.9

-1.4 -1.4

Bond length

25

C7-N1-C16 N1-C2-C3 N1-C2-C11 C3-C2-C11 C2-C3-C4 C2-C3-C8 C4-C3-C8 C3-C4-C5 C3-C4-H19 C5-C4-H19 C4-C5-C6 C4-C5-H20 C6-C5-H20 C5-C6-C7 C5-C6-C15 C7-C6-C15 N1-C7-C6 N1-C7-C12 C6-C7-C12 C3-C8-C9 C3-C8-H21 C9-C8-H21 C8-C9-C10 C8-C9-H22 C10-C9-H22 C9-C10-C11 C9-C10-H23 C11-C10-H23 C2-C11-C10 C2-C11-H24 C10-C11-H24 C7-C12-C13 C7-C12-H25 C13-C12-H25 C12-C13-C14 C12-C13-H26 C14-C13-H26 C13-C14-C15 C13-C14-H27 C15-C14-H27 C6-C15-C14 C6-C15-H28 C14-C15-H28 N1-C16-O17

118.7 119.8 119.8 120.4 122.3 118.3 119.4 126.8 115.4 117.6 127.5 117.3 115.1 122.6 119.0 118.4 119.5 120.0 120.6 121.2 119.0 119.8 119.9 119.9 120.2 119.7 120.4 120.0 120.5 118.8 120.8 120.3 118.9 120.8 119.9 119.9 120.3 119.8 120.2 120.0 121.1 119.1 119.8 122.2

118.5 120 119.7 120.3 122.8 118 119.2 127.4 115.1 117.1 128.2 116.8 114.8 123.2 118.8 118 119.6 119.9 120.5 121.5 118.6 119.9 119.9 119.9 120.2 119.7 120.4 119.9 120.6 118.6 120.8 120.4 118.8 120.8 119.9 119.8 120.3 119.8 120.3 120 121.4 118.7 119.9 122.5 26

120.9 119.6 119.2 121.2 123.0 117.3 119.7 126.6 115.0 117.8 128.0 118.0 113.6 123.0 119.4 117.6 119.1 120.4 120.5 121.7 118.4 119.9 120.1 119.9 120.1 120.0 122.3 117.7 119.7 119.2 121.0 120.6 119.7 119.7 119.9 120.1 120.0 119.8 120.4 119.9 121.7 116.5 121.8 121.5

2.4 -0.4 -0.5 0.9 0.2 -0.7 0.5 -0.8 -0.1 0.7 -0.2 1.2 -1.2 -0.2 0.6 -0.4 -0.5 0.5 0.0 0.2 -0.2 0.0 0.2 0.0 -0.1 0.3 1.9 -2.2 -0.9 0.6 0.2 0.2 0.9 -1.1 0.0 0.3 -0.3 0.0 0.1 -0.1 0.3 -2.2 1.9 -1.0

N1-C16-N18 O17-C16-N18 C16-N18-H29 C16-N18-H30 H29-N18-H30

115.9 121.9 121.0 113.6 117.2

115.2 122.3 119.6 112.5 116.2

116.0 122.5 121.5 119.0 119.3

0.8 0.2 1.9 6.5 3.1

Table 2 Experimental and calculated absorption wavelenght(λ), excitation energies(E), oscillator strength(f) and frontier orbital energies of Carbamazepine by HF/6-311++G(d,p) Time-Dependent method.

λ(Expt.;nm)

λ(Cal.;nm)

E(eV)

f

285.36

251.22

4.9353

0.2803

n→π*

-

222.05

5.5836

0.0013

π→π- *

213.84

216.27

5.7329

0.0024

π→π*

Assignment

EHOMO(eV)

ELUMO(eV)

EHOMO-1 (eV)

ELUMO+1 (eV)

-0.3030

-0.0336

-0.3339

-0.0418

Table 3 Calculated energy values of Carbamazepine by B3LYP/6-31G(d,p) method.

Basic set SCF energy (a.u.) Dipole moment µ (Debye)

B3LYP/6-31G(d,p) -763.5860 3.5469

EHOMO (eV)

-0.2123

ELUMO (eV)

-0.0499

EHOMO–LUMO gap (eV)

0.1625

EHOMO-1 (eV)

-0.2319

ELUMO +1(eV)

-0.0169

EHOMO-1 - LUMO+1 gap (eV) Chemical hardness (η) Softness (S) Chemical potential (µ) Electronegativity (χ ) Electrophilicity index (ω)

-0.215 -0.1311 -3.8139 -0.1311 0.1311 77.4661 27

Table 4 Mulliken and Natural Atomic charges of Carbamazepine

MPA Numbered Atom N1 C2 C3 C4 C5 C6 C8 C9 C10 C11 C12 C13 C14 C15 C16 O17 N18 H19 H20 H21 H22 H23 H24 H25 H26 H27 H28 H29 H30

DFT -0.624 0.114 0.162 -0.134 -0.117 0.155 -0.149 -0.074 -0.102 -0.063 -0.049 -0.103 -0.072 -0.148 0.714 -0.515 -0.634 0.09 0.094 0.089 0.089 0.092 0.1 0.095 0.087 0.085 0.084 0.265 0.275

RHF 0.979 0.369 -0.006 -0.146 -0.109 -0.016 -0.149 -0.157 -0.153 0.059 -0.205 -0.154 -0.147 -0.17 1.048 -0.645 -0.503 0.145 0.15 0.167 0.156 0.165 0.411 0.346 0.142 0.136 0.146 -0.484 0.309 28

NPA DFT -0.425 0.15 -0.086 -0.242 -0.195 -0.105 -0.200 -0.248 -0.248 -0.103 -0.281 -0.214 -0.244 -0.212 0.809 -0.656 -0.742 0.239 0.239 0.244 0.242 0.24 0.192 0.356 0.233 0.232 0.236 0.25 0.401

. RHF -0.525 0.196 -0.096 -0.246 -0.176 -0.144 -0.179 -0.255 -0.225 -0.097 -0.292 -0.21 -0.24 -0.212 0.994 -0.77 -0.831 0.233 0.234 0.242 0.239 0.238 0.184 0.382 0.229 0.227 0.23 0.269 0.407

Table 5 The dipole moments µ (D) polarizability α, the average polarizability α0, the anisotropy of the polarizability ∆α, and the first hyperpolarizability β of Carbamazepine calculated by B3LYP/6-31G(d,p) method. Parameters βxxx βxxy βxyy βyyy βzxx βxyz βzyy βxzz βyzz βzzz βtot (e.s.u) µx µy µz µ (D) αxx αxy αyy αxz αyz αzz (α) (e.s.u) ∆α (e.s.u)

B3LYP/6-31G(d,p) 664.0519 296.3815 217.5701 13.0332 33.3905 23.5960 -3.7106 10.3788 -2.0896 -2.3004 8.1543E –30 1.3645 0.2766 0.0343 1.3927 290.2780 22.4062 198.7063 0.6350 16.4955 57.3379 2.6988E –23 8.0370E –23

29

Table 6 Observed and theoretical vibrational assignments of Carbamazepine Calculated Wavenumber (cm-1)

Observed Wavenumber (cm-1)

RHF/6-31G(d,p) FTIR

FTRaman

3465

Assignments Unscaled

Scaled

Intensity

Unscaled

Scaled

Intensity

3979

3756 3640 3228 3223 3213 3212 3201 3200 3192 3189 3186 3169 1908 1816 1769 1765 1738 1735 1730 1636 1633 1597 1574 1534 1508 1437 1394 1365 1360 1350 1331 1292 1288 1259 1219 1209

63.1

3720

47.3

3592

11.3

3226

14.2

3216

25.1

3206

38.9

3205

20

3192

16.9

3191

20.8

3181

2.9

3180

1.1

3172

3527 3413 3084 3075 3066 3065 3054 3053 3044 3043 3036 3018 1762 1654 1625 1620 1592 1589 1586 1509 1504 1479 1456 1429 1374 1344 1333 1320 1290 1263 1254 1237 1220 1180 1176 1174

42.1 23.8 5.5 8.5 23.9 2.9 136 11.1 7.8 4.7 18.7 0.2 333.5 2.2 1.9 1.3 29.7 156.7 9.2 19.9 55.8 23.1 6.5 0.7 420.8 6.3 0.6 22.4 9.6 6.1 12.3 2.8 2.4 1.3 0.2 0.9

3848 3385 3380

3069

3070

3369 3368 3355 3354 3345 3342 3339

3020

3021

3320

1813

1953

1673

1856

1624

1806 1802

1594

1601

1774 1771 1765

1565

1667 1664

1488

1490

1626

1462

1461

1602

1435

1412

1560

1383

1533 1459 1414

1307

1309

1384 1379

1269 1245

1369 1250

1349 1309

1222 1203

B3LYP/6-31G(d,p)

1304 1274 1233 1223

0.7

3153

520.7

1799

1.5

1686

1.3

1655

3.4

1650

191.4

1621

36

1618

8.4

1614

65.5

1534

47.9

1529

17.9

1503

12.3

1479

2.4

1451

490.1

1394

16.5

1362

5.5

1351

5.3

1338

6.2

1306

5.1

1279

4.6

1269

0.7

1252

0.1

1234

2.7

1193

8.3

1189

8

1187

30

υNH2(100) υNH2(100) υCH(89) υCH2(92) υCH2(81) υCH3(87) υCH3(91) υCH3(96) υCH2(86) υCH2(87) υCH2(93) υCH2(99) υOC(77) υCC(61) υCC(62) υCC(66) υCC(20)+βCCC(11) βHNH(61) υCC(30) βHCC(30) βHCC(33) βHCC(10) βHCC(52) βHCC(53) υNC(54)+βOCN(13) υCC(41)+βHCC(10) υCC(52) υNC(42)+βHCC(11) υCC(12)+βHCC(32) υCC(12)+βHCC(34) υNC(11)+βHCC(11) υCC(33) υCC(10) υCC(10)+βHCC(29) βHCC(54) βHCC(22)

1151

1160

1211 1210

1115

1117

1204 1143 1141

1039

1025

1126

986

987

1118

1121 1116 1084 1077 1028 996 990 870

874

851

947 902

801

870 792

862 860 851

766

768

742

830 799

725

723

770

705

700

709

647

646

673

624

620

647

759

634 582

600

545

546

587 537 504

533

486

523

466

487 454

444 439

414

411

390

393

374

360

330

355

254

265

272

1198 1197

3.5

1146

8.1

1140

1191 1132 1130 1115 1110 1107 1105 1074 1067 1020

1.4

1110

2.4

1071

1.3

1068

0.6

1027

0.1

999

0.7

989

0.2

984

0.9

961

1

954

1.4

946

988 983 941 897 865 857 855 847 826 796 767 756 707 671 646 633 599 586 546 533 523 487

5.6

897

445 440 412 394 361 356 273 266

7.6

888

9.6

869

52.1

821

54.2

804

24.3

781

9.1

781

20.4

778

2.3

761

9.3

751

1

728

4.1

720

17.1

704

10

656

0.1

620

1.8

594

2

587

6.4

554

60.1

540

6.5

509

11.4

493

24.2

476

6.4

448

7.6

426

154.4

409

5.8

400

0.7

370

1.4

337

5

326

4

251

31

1135 1129

7 6.9

1100 1062 1059 1019 991 982 977 954 947 940

27 2.3 2.1 0.9 0.7 0.3 0.3 0.2 1.8 0.4

892 883 864 817 800 778 778 775 758 748 726 718 702 655 619 593 586 554 540 509 493 476

10.3 4.5 34.1 1.9 25.5 22.5 24.2 6.1 18.5 7.9 0.4 2.1 11.7 38.4 0.4 1.2 1.3 7.2 103.5 6 7.9

449 427 410 401 371 338 327 252

37.7 58.4 13.2 3.9 2.5 0.1 1.3 4

7.2

υCC(10)+βHCC(12) υCC(10)+βHCC(12) υ0C(10)+υNC(17) +βHNC(53) υCC(34) υCC(32) υNC(38) τHCCC(61)+τCCCC(10) τHCCC(51) τHCCC(54) τHCCC(27)+τHCCN(28) τHCCC(39) τHCCC(35) βCCC(18)+τHCCC(11)+ τHCCN(15) τHCCC(38)+τHCCN(10) βCCC(13)+τHCCC(30) τHCCC(18)+OOPCCCC(28) βCCC(29) τHCCC(59) τHCCC(59) τHCCC(43) OUT ONNC(22) OUT ONNC(63) τHCCC(29) βCCC(27) βCCC(37) βOCN(11)+βCCC(14) βCCC(1)+ βOCN(29) τCCCC(32) βCCC(15) τCCCC(30) βOCN(1) τHNHN(8) τCCCC(10) τCCCC(13)+OOPCCCC(10) βCCN(10)+βNCC(11)+ τHNCN(12) τHNCN(62) βNCN(41) τCCCC(20) υ NC(14) βCCN(21)+βNCC(26) βCNC(30)+τCCCC(17) βCNC(25) +τCCCC(32)

175 170

143

138

103

90

92 72

72

52

176 144 104

0.6

241

242 164 139

3.4 0.5 2.5

2.9

163

0.7

138

93 73

7.4

90

0.4

84

91 85

0.8 5.5

1.42

66

66

0.1

τCCCC(10)+OOPCCCC(13) τCCCC(13)+τCNCC(22) βCNC(31)+OOPNCCC(25) βCNC(13)+ τCCCN(15)+ τCCNC(35)+τNCNC(10) τNCNC(78) βCNC(19)+ τCCCN(18)+ oopCCCN(19)+oopNCCC(22)

Table 7 Thermodynamic properties at different temperatures for the Carbamazepine obtained by B3LYP/6-31G(d,p) method Temperature

S0m

C0p.m

∆H0 m

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

(cal mol-1 K-1) 321.52 405.85 486.45 487.97 569.6 648.72 723.87 794.5 860.61 922.49 980.48

(cal mo-1 K-1) 90.7 164.15 244.99 246.5 322.81 386.49 437.52 478.36 511.51 538.86 561.74

(K cal mol-1) 6.00 18.59 38.67 39.12 67.68 103.26 144.55 190.42 239.97 292.53 347.59

32

Table 8 The calculated thermodynamic parameters of Carbamazepine

Parameters

RHF/6-31G(d,p)

B3LYP/6-31G(d,p)

-758.57 160.097 0.693 0.376 0.317 0.03327 0.01805 0.01521

-763.35 149.33 0.691 0.371 0.303 0.03318 0.0178 0.01455

112.675 42.279 32.631 37.765

116.239 42.279 32.691 41.268

168.133 0.889 0.889 166.356

157.979 0.889 0.889 156.201

51.997 2.981 2.981 46.035 4.1164 -0.2954 0.091 0.3864

56.568 2.981 2.981 50.606 3.5469 -0.2123 -0.0499 0.1625

Total energy (a.u.) Zero-point energy (kcal/mol) Rotational constants (GHz)

Rotational temperature (K)

Entropy (cal/mol K) Total Translational Rotational Vibrational Enthalpy (kcal/mol) Total Translational Rotational Vibrational Specific heat capacity (cal/mol K) Total Translational Rotational Vibrational Dipole moment (Debye) HOMO (eV) LUMO (eV) Energy gap (eV)

33

Table 9 The calculated 13C and 1H NMR chemical shifts of Carbamazepine DFT

RHF

Atom position

C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 H19 H20 H21 H22 H23 H24 H25 H26 H27 H28 H29 H30

Absolute Shielding 57.8 66.8 67.0 58.3 72.3 55.5 62.0 71.3 73.7 39.7 42.7 58.5 69.0 65.0 46.8 26.5 26.3 25.1 25.1 24.7 3.5 7.4 24.2 25.0 25.3 2.1 24.9

Chemical Shifts 142.1 133.1 132.8 141.5 127.6 144.4 137.9 128.6 126.2 160.2 157.2 141.3 130.9 134.9 153.1 6.0 6.2 7.4 7.4 7.8 29.0 25.1 8.3 7.5 7.2 30.4 7.6

Absolute Shielding 61.9 74.5 77.1 65.5 79.1 62.9 64.3 77.0 76.1 45.8 48.6 63.5 72.9 71.3 43.8 26.4 26.1 24.7 25.0 24.5 -3.9 5.6 24.2 25.0 25.1 -5.9 25.3

34

Chemical Shifts 138.0 125.4 122.8 134.4 120.8 136.9 135.6 122.9 123.8 154.1 151.3 136.4 127.0 128.6 156.1 6.1 6.9 7.8 7.5 8.0 36.5 26.9 8.3 7.5 7.4 38.5 7.2

Experimental values 140.0 129.5 77.3 135.1 130.5 77.0 76.6 129.6 127.7 128.7 157.3 6.96 7.35 7.49 7.44 7.46 7.28 7.32 7.5 7.43 7.39 7.34 7.38

Graphical Abstract

35

HIGHLIGHTS


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

36