CHAPTER – 6

VIBRATIONAL FREQUENCIES, STRUCTURAL

CONFIRMATION STABILITY AND HOMO-LUMO ANALYSIS

OF NICOTINIC ACID ETHYL ESTER WITH EXPERIMENTAL

(FT-IR AND FT-RAMAN) TECHNIQUES AND QUANTUM

MECHANICAL CALCULATIONS

6.1. INTRODUCTION

The use of nicotinic acid derivatives in the field of medicinal, biomedical

industries, production of cosmetics, pesticides, agro chemical industries and its

biological activities have been studied extensively over the past decades. In this

chapter, one of such nicotinic acid derivative called Nicotinic Acid Ethyl Ester (also

known ethyl nicotinate, Ethyl 3-pyridinecarboxylate and 3-pyridinecarboxylic acid,

ethyl ester) have been choosen for the study so as to interpret its vibrational

frequencies, structural conformational stabilities, thermal properties, HOMO-LUMO

analysis using FTIR and FT-Raman Spectra. In this title molecule, the H atom in the

nicotinic acid was replaced by CH2-CH3 group

Due to the existence of a lone pair of electrons on the nitrogen atom, pyridine

may be regarded as a good probe molecule and also a strong electron donor. The

vibrational frequency shifts of the internal modes, which are sensitive to the

interaction between pyridine and an electron acceptor, reflect the nature of the

interaction of donor-acceptor and are indicative of the change of the acceptor

properties. The in-plane force field and vibrational spectra of pyridine [1], vibrational

spectra of mono substituted pyridines [2] and density functional study with normal

mode analysis of the bindings and vibrational frequency shifts of the pyridine-metal

complexes [3] and vibrational field and intensities for pyridine [4] were

comprehensively studied by the earlier workers.

6.2. LITERATURE SURVEY

Various spectroscopic studies of nicotinic acid and its derivates have been

reported in the literature. The crystal structure of nicotinic acid was first determined in

1953 [5] and subsequently reinvestigated [6]. Nicotinic acid has been studied

extensively by optical vibrational spectroscopy in the past [7-9]. The picolinic [10],

nicotinic [11] and isonicotinic acids [12] and its complexes with different metals were

thoroughly investigated by different methods. Earlier, Koczon et al [13] discussed the

experimental and theoretical vibrational frequency and interpreted IR and Raman

spectra in the range between 1350-3437 cm-1

for picolinic, nicotinic and isonicotinic

acids. Park et al [14] studied the adsorption of picolinic acid and nicotinic acid on a

silver sol surface has been investigated over a wide range of solution of pH by surface

enhanced Raman scattering. Metal halide complexes of isonicotinic acid were

extensively studied by the earlier workers [15-17]. Wang [18] was carried out

experimental (UV and Raman) and theoretical study (DFT) of pyridine carboxylic

acid (isonicotinic acid) in aqueous solution.

Experimental and theoretical relationship between energetics and structure of

nicotinic acid was studied by Goncalves et al [19]. Hudson et al [20] investigated

nicotinic acid with inelastic neutron scattering spectrum and its assignments were

made using density functional theory. Sala et al [21] studied the vibrational analysis

of nicotinic acid in the range 400-1725 cm-1

. The investigation of molecular structure

and vibration frequencies of 2-choloronicotinic acid and 6-chloronicotinic acid

molecules with FT-IR and FT-Raman spectroscopy and quantum chemical

calculations were carried out by Karabacak et al. [22-23]. Ab initio studies of

molecular structures, conformers and vibrational spectra of heterocyclic organics

(Nicotinamide and its N-oxide) were studied by Kumar et al [24]. Vibrational study of

Nicotinic Acid complexes with different central ions were studied by Lewandowski et

al [25]. Seliger et. al. [26] studied

14N nuclear quadrupole resonance of picolinic,

nicotinic, isonicotinic and dinicotinic acids. Experimental and theoretical UV, NMR,

and vibrational features of nicotinic acid N-oxide and nicotinamide N-oxide

molecules were studied by Atac et. al. [27-28].

To the best of our knowledge, neither quantum mechanical calculations nor

the vibrational spectra of Nicotinic Acid Ethyl Ester (also known ethyl nicotinate,

Ethyl 3-pyridinecarboxylate and 3-pyridinecarboxylic acid, ethyl ester) have been

reported up to now. Due to this scantiness observed in the literature persuaded us to

make this theoretical and experimental vibrational spectroscopic research to give a

correct assignment of the fundamental bands in the experimental FT-IR and FT-

Raman spectra on the basis of the calculated total energy distribution (TED) using

Pulay‘s Density Functional Theory (DFT) based on scaled quantum chemical

approach [29], ab initio HF, DFT/B3LYP and DFT/LSDA using different basis sets.

Moreover, in the present study, the effects have been taken to predict a complete

description of the molecular geometry, molecular vibrations, rotational constants,

atomic charges and HOMO-LUMO energies of NAEE. The thermodynamic

properties of the title compound at different temperatures have been calculated,

revealing the correlations between heat capacity, entropy, enthalpy changes and

temperatures.

6.3. COMPUTATIONAL DETAILS

The primary task for the computational work was to determine the

optimized geometry of the compound. The molecular structure optimization of the

title compound and corresponding vibrational harmonic frequencies were calculated

using HF, B3LYP and LSDA methods with 6-311G(d,p) and 6-311++G(d,p) basis

sets using GAUSSIAN 03 program package without any constraint on the geometry.

The stability of the optimized geometries was confirmed by wavenumber

calculations, which gave positive values for all the obtained wavenumbers. TED

calculations, which show the relative contributions of the redundant internal

coordinates to each normal vibrational mode of the molecule and thus enable us

numerically to describe the character of each mode, were carried out by the Scaled

Quantum Mechanical (SQM) method using PQS program in which the output files

created at the end of the wavenumber calculations. The optimized geometrical

parameters, true rotational constants, fundamental vibrational frequencies, IR and

Raman intensity, Raman activity, atomic charges, dipole moment, and other thermo

dynamical parameters were calculated using the Gaussian 03 package . By combining

the results of the GAUSSVIEW program with symmetry considerations, vibrational

frequency assignments were made with a high degree of accuracy.

The electronic properties, such as HOMO-LUMO energies, absorption

wavelengths and oscillator strengths were calculated using B3LYP method of TD-

DFT, basing on the optimized structure in solvent (DMSO and chloroform) and gas

phase. The changes in the thermodynamic functions such as the heat capacity,

entropy, and enthalpy were investigated for the different temperatures from the

vibrational frequencies calculations of the title molecule.

6.3.1. Prediction of Raman Intensities

The Raman activities (SRa) calculated with the Gaussian 03 program were

converted to relative Raman intensities (IRa) using the following relationship derived

from the intensity theory of Raman scattering [30,31].

𝐼𝑅𝑎 =𝑓 𝜈𝑜−𝜈𝑖

4𝑆𝑖

𝜈𝑖 1−exp (−𝑕𝑐𝜈𝑖𝑘𝑇

) …… 6.1

Where, νo is the laser exciting wavenumber in cm−1

(in this work, we have used the

excitation wavenumber νo = 9398.5 cm−1

, which corresponds to the wavelength of

1064 nm of a Nd : YAG laser), νi the vibrational wavenumber of the ith

normal mode

(in cm−1

) and Si is the Raman scattering activity of the normal mode νi, f (is a constant

equal to 10−12

) is a suitably chosen common normalization factor for all peak

intensities. h, k, c and T are Planck constant, Boltzmann constant, speed of light and

temperature in Kelvin, respectively.

6.4. RESULTS AND DISCUSSION

6.4.1. Molecular Geometry

NAEE may have two possible structures in connection with the ethyl ester

group orientations of the oxygen atom in the acid group. The conformer C1 is

predicted to be from 0.301 kcal/mol more stable than the C2 conformer. Therefore, in

this section, we tabulated only C1 conformer calculations data. The conformers along

with numbering of atoms of NAEE are as shown in Fig 6.1. The optimized molecular

geometries for NAEE by HF and DFT (B3LYP, LSDA) methods with different basis

sets and the experimental data are tabulated in Table 6.1. The bondlength variation

between the atoms of the molecule is graphically represented in Fig. 6.3.Since there is

no vibrational and quantum mechanical calculations yet in NAEE, the crystal

structure and microwave study of nicotinic acid and pyridine were taken as reference

values [32-35]. However, significant variations are noticed in the magnitudes of some

of the bond lengths and bond angles. According to Pang [32] addition of the

polarization function has the effects on the pyridine ring as that (a) the angle at the

nitrogen atom is decreased slightly (b) the bond distances involving nitrogen directly

are decreased slightly, leading to a slightly different basis set offset value, and (c)

other more remote distances and angles in the molecule show only very small

alterations. The CN bond distance N1-C2 evaluated in the present work with

DFT(B3LYP, LSDA) methods are 1.337 and 1.330 Å for both the basis sets,

respectively. However, HF method calculated at 1.320 Å. Similarly for N1-C6, it is

1.335 Å (B3LYP) and 1.327 Å (LSDA) with the 6-311++G(d,p) basis set. The bond

distance obtained between C2-N1 by DFT/B3LYP method has excellent agreement

with the previously reported microwave result of Mata [34]. But, the C6-N1 bond

distance obtained in this work by B3LYP method has a slight decrease of 0.01 Å with

the earlier experimental data [40] may be due to the substitutions in the C5 site of the

pyridine ring. From the calculated bond lengths of four CC moieties of the pyridine

ring, it is clear that the values lie within range of 1.379–1.389 Å for HF, 1.388-1.400

Å for B3LYP and 1.380-1.392 Å for LSDA methods. From the bond lengths values

occurred in this study illustrates that the substitution in the pyridine ring produces a

considerable increase of bond lengths between C4-C5 and C5-C6 moieties than the

other CC bond lengths in the pyridine ring. The bond distance obtained between C5-

C11 by DFT/B3LYP method has only a marginal difference of 0.002 Å with the

experimental data [35]. Similarly, for the four CH bond lengths, the values lie in the

range of 1.074–1.077 Å (HF), 1.083–1.087 Å (B3LYP) and 1.093–1.097 Å (LSDA)

and all the CH bond lengths are identical in the pyridine ring. By analyzing the

theoretical and experimental bond lengths between CN, CC and CH of the title

molecule, the DFT/B3LYP method shows a better coincidence with experimental one

with the marginal difference of 0.001–0.007 Å. The bond lengths for C-O and C=O

obtained in the present work by DFT methods agree well with the experimental data

reported in the literatures [5,33].

The optimized bond angles of CCC in the pyridine ring ranges from 118.080 to

118.700 and CNC varies from 117.39

0 to 117.87

0 whereas the CCN bond angles are

found to be little higher by 40

to hexagonal angle 1200 in both HF and DFT theories

which is in close agreement with the earlier literature [22]. Moreover, this study

concludes that the theoretically calculated bond lengths and bond angles are agrees

well with the earlier references [22,32-34].

6.4.2. Potential energy surface scan

In order to describe conformational flexibility of the title molecule, the energy

profile as a function of O12-C11-C5-C6 torsion angle was achieved with B3LYP/6-

311G(d,p) method (Fig. 2). According to theoretical study T (O12-C11-C5-C6) is 00

and 1800 for DFT/B3LYP/6-311G(d,p), the conformational energy profile shows two

maxima near 900 and 270

0 for O12-C11-C5-C6 torsion angle. The maximum energies

are obtained -515.60569964 and -515.605699668 Hartree for 900 and 270

0 dihedral

angles, respectively. It is clear from Fig.6.2, there are two local minima (stable

conformers) observed at 00 (-515.616770768 Hartree) and 180

0 (-515.617251229

Hartree) for T (O12-C11-C5-C6). Therefore, the most stable conformer is obtained

for 1800 torsion angle for O12-C11-C5-C6 rotation.

6.4.3. Vibrational assignments

The NAEE consists of 20 atoms, and belongs to CS symmetry. Hence the

number of normal modes of vibrations for NAEE works to 54 (3N-6). Of the 54

normal modes of vibrations, 36 modes of vibrations are in plane and remaining 18

modes are out of plane. The bands that belong to the in-plane modes are represented

as A′ while the out-of-plane modes as A

″. Thus the 54 normal modes of vibrations are

distributed as ΓVib=36A′+18A

″.

In order to obtain the spectroscopic signature of NAAE molecule, the

wavenumber calculation analysis is performed using HF and DFT (B3LYP and

LSDA) theories with different basis sets. Calculations were made for gaseous phase,

where as the experiments were performed for solid phase. Therefore, there is some

disagreement between the calculated and observed vibrational wavenumbers.

The comparative data of FT-IR and FT-Raman experimental frequencies,

unscaled and scaled vibrational frequencies of NAEE using Ab initio HF, and DFT

(B3LYP and LSDA) methods with different basis sets are listed in Table 6.2.

Calculated Raman and IR intensities help us to distinguish and more precisely assign

those fundamentals which are close in frequency. Experimental FT-IR and FT-Raman

spectrum of NAEE are shown in Figs. 6.4 and 6.5, respectively. The TED for each

normal mode among the symmetry coordinates of the molecule was calculated. In

Table 6.2, the last column gives a detailed description of the normal modes based on

the TED.

The calculated harmonic force constants and wavenumbers are usually higher

than the corresponding experimental quantities because of the combination of electron

correlation effects and basis set deficiencies. The observed slight disagreement

between theory and experiment could be a consequence of the anharmonicity and the

general tendency of the quantum mechanical methods to overestimate the force

constants at the exact equilibrium geometry. Nevertheless, after applying uniform

scaling factors, the theoretical calculation reproduces the experimental data well.

Therefore, in order to improve the calculated values in agreement with the

experimental values, it is necessary to adjust the calculated frequency so as to give a

―best fit‖ to the observed experimental frequency. Hence, the vibrational frequencies

calculated at DFT (B3LYP and LSDA) level are scaled by 0.9668, 0.9614, 0.9877 for

different basis sets and the scaling factors which are 0.9085 (6-311G(d,p) and 0.9051

(6-311++G(d,p) are used in HF method [36].

Listed in Table 6.3, are the mean deviation, mean absolute deviation, Root

Mean Square values and correlation coefficients of the vibrational frequencies

(unscaled and scaled) for this title molecule with different computational methods.

Table 6.4 indicates that the mean deviation and mean absolute deviation between the

calculated (scaled) and experimental frequencies are 22.7, 19.2 cm-1

and 22.4,

16.9 cm-1

for B3LYP with different basis sets respectively; The mean and absolute

deviation calculated for other methods (LSDA, HF) are greater when compared with

B3LYP method. In addition, the correlation coefficient between the experimental and

scaled calculated frequencies shows that B3LYP method gives better result than the

other methods. Hence, it is concluded that the hierarchy in the coincidence of

experimental frequencies with calculated one are B3LYP > LSDA > HF respectively.

This overestimation of frequency may be from the formation of intermolecular

hydrogen bonding and also it should be noted that the theoretical results belong to

solid phase whereas the experimental results belong to gaseous phase. Furthermore,

the treatment of scaling factors to the calculated frequencies increases its harmony

better with the experimental values.

6.4.3.1. C-H Vibrations

The heteroatomic structure shows the presence of C-H stretching vibrations in

the region 3100–3000 cm-1

which is the characteristic region for ready identification

of C-H stretching vibrations and these vibrations are not found to be affected due to

the nature and position of the substituent [37]. Most of the aromatic compounds have

nearly four infrared peaks in the region 3080–3010 cm-1

due to ring C-H stretching

bonds [38-39]. This molecule has four adjacent C-H moieties in the pyridine ring and

the expected four C-H stretching vibrations are C2-H7, C3-H8, C4-H9 and C6-H10

(modes 1-4). Accordingly, the symmetric stretching vibrations are observed at 3110

cm-1

and 3070 cm-1

in the FT-Raman spectrum whereas in FT-IR, it is assigned at

3090 cm-1

and 3050 cm-1

. The magnitude of C-H stretching frequency (mode 1) is

higher than the normal expected value is due to the presence of substituent in the

neighboring atom. The value of Raman activity to the corresponding mode is also

very high implies that the band become more polarized. In general, most of the

stretching modes are pure stretching modes as is evident from TED column in Table

6.2; they almost contribute ca. 100%.

If we consider TED calculations out-of-plane bending vibrations are assigned

as pure modes and in-plane bending vibrations are mixed modes. In this study, most

of the C-H in-plane bending vibrations are mixed vibrations with CC and CN with

strong and medium intensity sharp bands in the region 1000-1470 cm-1

. In view of

that, in this present work, the peaks at 1200 (m) in both, 1095 (FT-R), 1040 (FT-R)

and 1030 (FTIR) cm-1

are assigned as C-H in-plane-bending vibrations. The

substitution patterns on the ring can be judged from the out of plane bending of the

ring C-H bond in the region 900-675 cm-1

which are more informative [40]. Besides,

the C-H out-of-plane bending vibrations are strongly coupled vibrations and occur in

the region 900-667cm-1

[41]. In the present study, the peaks at 980(w), 950(w) and

820(m) cm-1

in FT-IR and 940 cm-1

in FT-Raman confirm the C-H out of plane

bending vibrations which agrees well with the above said literature values.

6.4.3.2. C-C Vibrations

The ring stretching vibrations are very much important in the spectrum of

pyridine and its derivatives, and are highly characteristic of the aromatic ring itself.

The aromatic ring carbon-carbon stretching vibrations occur in the region 1430-1650

cm-1

[42-43]. As predicted in the earlier references, in the present work the strong

C=C aromatic stretch is observed in the region 1600 cm-1

in FT-IR and 1590 cm-1

in

FT-Raman spectrum, respectively. The C-C stretching vibrations normally occurred

as coupled vibrations and shows vibrations in the range 1300 – 1400 cm-1

. Here too,

the C-C stretching vibrations are noted at 1400 cm-1

and 1290 cm-1

. One of the C-C

vibration has value less than 10 cm-1

from the expected range indicates that it is

affected by the presence of substitution in that corresponding position. A strong band

in FT-IR spectrum at 705 cm-1

is assigned to C-C-C bending mode.

6.4.3.3. C-N vibrations

Due to the overlapping of other vibrations in the pyridine ring, it is very

difficult to identify the CN vibrations easily. For nicotinamide N-oxide, C=N and

C–N stretching vibrations are observed at 742–1568 cm−1

in FT-IR and at 936–1594

cm−1

in FT-Raman spectra, respectively [27]. Sajan et al [44] observed C–N

stretching vibrations at 1412 cm−1

in FT-Raman, 1411 cm−1

in FT-IR and calculated

theoretically at 1425 cm−1

. In this study, these bands are assigned at 1030-1600 cm-1

in FT-IR and 1030-1590 cm-1

in FT-Raman, respectively. As stated in the earlier

studies, here, the C=N and C-N stretching vibrations are noted at 1470 cm-1

(FT-

Raman), 1260 cm-1

respectively. The all other C-N vibrations are mixed vibrations as

shown in the TED column in Table 6.2. The medium and strong intensity in FT-IR

and FT-Raman spectra at 620 cm-1

is assigned to CNC in-plane bending mode which

referred as ring deformation.

6.4.3.4. Ethyl group vibrations

In ethyl groups, the asymmetric stretch is usually at higher wavenumber than

the symmetric stretch. In this present work, the weak intensity peak at 2900 cm-1

in

both and FT-IR and FT-Raman spectra is assigned to CH3 symmetric stretching

vibration, whereas CH3 asymmetric frequencies are assigned at 3020 cm−1

and 2990

cm−1

in FT-IR. Moreover, in this molecule, the strong peaks in FT-Raman at 2940 and

2980 cm-1

are due to CH2 symmetric and asymmetric stretching modes, respectively,

which are in agreement with the literature [45-46]. In this molecule, the methyl in-

plane bending vibrations are noted at 1450 cm-1

(FTIR), 1370 cm-1

(both) and 1050

cm-1

while the out-of-plane bending vibrations are reported at 1420 cm-1

(FTIR), 860

cm-1

(FTIR), 790 cm-1

(both).

The peak at 1480 cm−1

is assigned to in-plane bending vibration of CH2 of

ethyl group. This is comparatively larger than the normal methelene vibrations. Also,

instead of getting two in-plane vibrations, here only one vibration is assigned because,

the other vibration is coupled with CH3 in-plane bending vibrations. The same case is

also noted in the earlier literature of [52] in which O-ethyl benzoylthiocarbamate has

one CH2 vibration instead of two. The CH2 out-of plane vibrations such as twisting

and waging vibrations are assigned at 1250 cm-1 and 1170 cm-1 of FTIR

respectively. In this study, the C-CH3 out-of-plane bending vibration is assigned to the

strong FT-Raman band of 200 cm-1

. The ethyl stretching vibration ie., between CH3

and CH2 is assigned to the medium intensity FT-Raman peak of 1020 cm-1

. All other

modes of ethyl group are mixed with phenyl ring and ester groups which are shown

clearly in the TED column of Table 6.2.

6.4.3.5. C=O and C-O vibrations

The C=O bond formed by - between C and O, internal hydrogen bonding

reduces the frequencies of the C=O stretching absorption to a greater degree than does

intermolecular H bonding because of the different electro negativities of C and O, the

bonding are not equally distributed between the two atoms. Generally, in esters, the

intense C=O stretching vibration occurs at higher frequencies. The Force constant of

the carbonyl bond is increased by the electron attracting nature of the adjacent atom

due to inductive effect. The band observed in the 1700–1800 cm−1

region due to the

C=O stretching vibration is one of the characteristic features of the carboxylic group

[27,28,37-42]. In this present study, a very strong band observed in both spectra at

1720 cm−1

(mode no. 10) is assigned to C=O stretching vibrations whereas the scaled

B3LYP predicted value is 1723 cm−1

shows a small deviation of about ca. 3 cm−1

and

the TED value of 90% as reported in Table 6.2.

The C–O stretching vibration ie.,C11-O13 is assigned to 1110 cm−1

in both

spectra which has the TED value of 58%. The strong band in Raman spectrum is

assigned to O-C=O bending vibration (850 cm-1

) and C-C-O vibration is assigned to

weak 390 cm-1

band. Most of the C–O vibrations are mixed vibrations as shown in the

TED values in Table 6.2. The remainders of the observed and calculated frequencies

are accounted in Table 6.2.

6.4.4. Thermodynamic properties

The variation in Zero-Point Vibrational Energies (ZPVEs) seems to be

significant. The values of some thermodynamic parameters (such as zero-point

vibrational energy, thermal energy, specific heat capacity, rotational constants,

entropy, and dipole moment) of NAEE by HF and DFT (B3LYP/LSDA) with 6-

311G(d,p)/6-311++G(d,p) method at 298.150 K and 1.00 Atm pressure are listed in

the Table 6.4. The ZPVE energy is much lower in the DFT/LSDA method than by

other methods. The biggest value of ZPVE of NAEE is 107.26125 kcal mol-1

obtained

at HF/6-311G(d,p) whereas the smallest one is 97.67361 kcal mol-1

obtained at

DFT/LSDA/6-311++G(d,p) method.

On the basis of vibrational analysis at B3LYP/6-311++G(d,p) level, the

standard statistical thermodynamic functions: heat capacity 𝐶𝑝 ,𝑚0 , entropy 𝑆𝑚

0 and

enthalpy changes ∆𝐻𝑚0 for the title compound were obtained from the theoretical

harmonic frequencies and listed in Table 6.5. From Table 6.5, it can be observed that

these thermodynamic functions are increasing with temperature ranging from 100 to

700 K due to the fact that the molecular vibrational intensities increase with

temperature [47]. The correlation equations between heat capacity, entropy, enthalpy

changes and temperatures were fitted by quadratic formulas, and the corresponding

fitting factors (R2) for these thermodynamic properties are 0.9986, 0.9998 and 0.9999,

respectively. The corresponding fitting equations are as follows and the correlation

graphs are as shown in Figs. 6.6–6.8.

)9986.0R(T10x7015.3T1247.03286.3C 2250m,p

…… 6.2

)9998.0(109938.31575.08438.56 2250 RTxTSm …… 6.3

)9999.0(108779.40096.02062.0 2250 RTxTHm …… 6.4

All the thermodynamic data supply helpful information for the further study

on the NAEE. They can be used to compute the other thermodynamic energies

according to relationships of thermodynamic functions and estimate directions of

chemical reactions according to the second law of thermodynamics in

Thermochemical field. Notice: all thermodynamic calculations were done in gas

phase and they could not be used in solution.

Dipole moment reflects the molecular charge distribution and is given as a

vector in three dimensions. Therefore, it can be used as illustrator to depict the charge

movement across the molecule. Direction of the dipole moment vector in a molecule

depends on the centres of negative and positive charges. Dipole moments are strictly

identified for neutral molecules. For charged systems, its value depends on the choice

of origin and molecular orientation. As a result of HF and DFT (LSDA/B3LYP)

calculations the highest dipole moment was observed 0.6964 at LSDA/6-311++G(d,p)

whereas the smallest one was observed 0.4225 HF/6-311G(d,p) in NAEE.

6.4.5. UV-VIS spectral studies and Frontier molecular orbitals (FMOs)

The total energy, energy gap and dipole moment have influence on the

stability of a molecule. We have performed optimization in order to investigate the

energetic behavior and dipole moment of title compound. Ultraviolet spectra analyses

of NAEE have been investigated in gas phase and in two different organic solvents

(DMSO and CHCl3) by theoretical calculation and are within 200–400 nm range. The

calculated excitation energies, oscillator strength (f) and wavelength () and spectral

assignments are given in Table 6.7. The major contributions of the transitions were

designated with the aid of SWizard program [48]. The theoretical absorption

wavelengths (in gas phase and solvent) are compared in Table 6.6. Due to the Frank–

Condon principle, the maximum absorption peak (max) in an UV–Visible spectrum

corresponds to vertical excitation. TD-DFT calculations predict three transitions in the

UV–VIS region for NAEE molecule. The strong transitions at 4.2611 eV (290.97 nm)

with an oscillator strength f=0.0006 in gas phase, at 4.4134 eV (280.93 nm) with an

oscillator strength f=0.0007 and at 4.3672 eV (283.90 nm) with an oscillator strength

f=0.0007 in DMSO and Chloroform and, respectively, are assigned to a π–π*

transition. In view of calculated absorption spectra, the maximum absorption

wavelength corresponds to the electronic transition from the highest occupied

molecular orbital HOMO-1 to lowest unoccupied molecular orbital LUMO with 95%

contribution. However, the second one corresponds to HOMO-LUMO with 95%

contribution, is assigned to a π–π* transition. The other wavelengths, excitation

energies, oscillator strength and calculated counterparts with major contributions can

be seen in Table 6.7.

The frontier molecular orbitals, HOMO and LUMO and frontier orbital gap

helps to exemplify the chemical reactivity and kinetic stability of the molecules, and

are important parameters for quantum chemistry [49]. 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. In order to evaluate the energetic behavior of the title compound,

we carried out calculations in gas and in solvent (DMSO and Chloroform). HOMO,

HOMO-1, LUMO and LUMO+1 energies and orbital energy gaps calculated by TD-

DFT/B3LYP/6-311G++(d,p) in solvent (DMSO and Chloroform) and Gas phase are

presented in Table 6.6. The 3D plots of the frontier orbitals namely ground state

(HOMO), HOMO-1 and excited state (LUMO) are shown in Fig. 6.9. The positive

phase is red and the negative one is green. It can be seen from the plots that the

HOMO levels are spread over the entire molecule expect the CH2 and CH3 groups in

ground state and all positive and negative phase are distributed unsymmetrical. The

LUMO of first excited state is almost uniformly distributed over the molecule without

methyl and methylene group, and all positive and negative phase are distributed

symmetrically. The energy gap of HOMO–LUMO explains the eventual charge

transfer interaction within the molecule, which influences the biological activity of the

molecule. Furthermore, in going from the gas phase to the solvent phase, the

increasing value of the energy gap and molecule becomes more stable. This electronic

absorption corresponds that is mainly described by one electron excitation from the

highest occupied molecular or orbital (LUMO). The frontier orbital gap in case of

NAEE is found to be 5.46708, 5.57185, 5.61647 eV for DMSO, Chloroform and gas

phase, respectively. The decrease in energy gap between HOMO and LUMO

facilitates intramolecular charge transfer which makes the material to be NLO active.

Moreover, we calculated dipole moment in gas phase and solution. Dipole

moment reflects the molecular charge distribution. It is seen from Table 6.6, the

dipole moment value increases going from the gas phase to the solvent phase.

6.4.6. Molecular electrostatic potential

In the present study, 3D plots of molecular electrostatic potential (MEP) of

NAEE is illustrated in Fig. 6.10. The MEP which is a plot of electrostatic potential

mapped onto the constant electron density surface. The MEP is a useful property to

study reactivity given that an approaching electrophile will be attracted to negative. In

the majority of the MEPs, while the maximum negative region which preferred site

for electrophilic attack indications as red colour, the maximum positive region which

preferred site for nucleophilic attack symptoms as blue colour. The importance of

MEP lies in the fact that it simultaneously displays molecular size, shape as well as

positive, negative and neutral electrostatic potential regions in terms of colour grading

(Fig. 6.10) and is very useful in research of molecular structure with its

physiochemical property relationship [50-51]. The resulting surface simultaneously

displays molecular size and shape and electrostatic potential value.

The different values of the electrostatic potential at the surface are represented

by different colors. Potential increases in the order red < orange < yellow < green <

blue. The color code of these maps is in the range between -0.04571 a.u. (deepest red)

to 0.04571 a.u. (deepest blue) in compound, where blue indicates the strongest

attraction and red indicates the strongest repulsion. Regions of negative V(r) are

usually associated with the lone pair of electronegative atoms. As can be seen from

the MEP map of the title molecule, while regions having the negative potential are

over the electronegative atom (Oxygen atoms), the regions having the positive

potential are over the hydrogen atoms. If compared, the negative potential value is

-0.0456747 a.u. for O12 and -0.0442044 a.u. for N1 atoms. A maximum positive

region localized on the H atoms in the ring has value of +0.0244286 a.u. and the other

one is localized on the H atoms in the CH2 and CH3 groups has value of +0.0189862

a.u. According to these calculated results, the MEP map shows that the negative

potential sites are on oxygen atoms as well as the positive potential sites are around

the hydrogen atoms.

6.5. CONCLUSION

The FT-IR and FT-Raman spectra have been recorded and the detailed

vibrational assignment is presented for NAEE. The equilibrium geometries, harmonic

vibrational frequencies, IR and Raman spectra of NAEE are determined and analyzed

by ab initio-HF and DFT (LSDA and B3LYP) with 6-311G(d,p) and 6-311++G(d,p)

basis sets. The difference between the observed and calculated wavenumbers is very

small for most of fundamentals. A detailed interpretation of the infrared spectra of

was also reported more precisely. The MEP, charge transfer between HOMO and

LUMO energies, frontier energy gap are calculated and presented. The present

quantum mechanical study may further play an important role in understanding of

dynamics of this molecule. Some of the significant results obtained regarding this

molecule are given below.

This molecule has two possible structures in connection with the ethyl ester

group orientations of the oxygen atom in the acid group. With the aid of

potential energy surface scan, the conformational energy profile shows two

maxima near 900 and 270

0 for O-C-C-C torsion angle and moreover, the

maximum energies obtained are -515.60569964, -515.605699668 Hartree

respectively. Moreover, there are two local minima (stable conformers)

observed at 00 (-515.616770768 Hartree) and 180

0 (-515.617251229 Hartree)

for T (O-C-C-C) which confirms that the most stable conformer is for 1800

torsion angle for O-C-C-C rotation.

By analyzing the optimized bond angles and bond lengths, significant

variations are noticed in the magnitudes of some of the bond lengths and bond

angles such as the addition of the polarization function has the effects on the

pyridine ring, the angle at the nitrogen atom is decreased slightly and the bond

distances involving nitrogen directly are decreased slightly, leading to a

slightly different basis sets. C-N bond distance obtained in this work by

B3LYP method has a slight decrease of 0.01 Å with the earlier experimental

data may be due to the substitutions in the C5 site of the pyridine ring.

The optimized bond angles of CCC in the pyridine ring ranges from 118.080 to

118.700 and CNC varies from 117.39

0 to 117.87

0 whereas the CCN bond

angles are found to be little higher by 40

to hexagonal angle 1200 in both HF

and DFT theories.

The bond length values occurred in this study illustrates that the bond lengths

between the C-C moieties where the substitution the substitution in the

pyridine ring produces a considerable increase of bond lengths between the

C-C moieties where it is connected than the other CC bond lengths in the ring.

By employing the statistical tools to the vibrational frequencies (theoretical &

experimental), it is inferred that the mean and absolute deviation calculated

for LSDA, HF are greater when compared with B3LYP method whereas the

correlation coefficient between the frequencies shows that B3LYP method

gives better result than the other methods which concludes that the hierarchy

in the coincidence of experimental frequencies with calculated one are B3LYP

> LSDA > HF respectively.

The CH stretching vibrations are within the expected range except one

vibration. The magnitude of its stretching frequency is higher than the normal

expected value by 10 cm-1

is due to the effect of substituent in the neighboring

atom. Also, the value of Raman activity to the corresponding mode is very

high implies that the band become more polarized.

The entire C=C, C-C, C=N and C-N vibrations are occurred in the expected

range. However, one of the C-C vibration has value less than 10 cm-1

from the

expected range indicates that it is affected by the presence of substitution in

that corresponding position

The ethyl group vibrations (CH3 and CH2) are occurred well within in the

expected range. However, instead of getting two in-plane vibrations, only one

vibration is observed confirms that, the other missing vibration is coupled with

CH3 in-plane bending vibrations.

A very strong C=O stretching band observed in both spectra at 1720 cm−1

deviates by about ca. 5 cm-1

with TED of 90% calculated from B3LYP method

confirms the force constant of the carbonyl bond is increased by the electron

attracting nature of the adjacent atom due to inductive effect.

As a result of HF and DFT (LSDA/B3LYP) calculations the highest dipole

moment was observed at LSDA/6-311++G(d,p) whereas the smallest one was

observed 0.4225 HF/6-311G(d,p) method which proved that there is the

charge movement across the molecule and the dipole moment value increases

going from the gas phase to the solvent phase.

The thermodynamic properties of the title compound at different temperatures

have been calculated. It is seen that the heat capacities, entropies and

enthalpies increase with the increasing temperature owing to the intensities of

the molecular vibrations increase with increasing temperature.

In view of calculated absorption spectra with TD-DFT/B3LYP/

6-311++G(d,p), the maximum absorption wavelength corresponds to the

electronic transition from the highest occupied molecular orbital HOMO-1 to

lowest unoccupied molecular orbital LUMO with 95% contribution. However,

the second one corresponds to HOMO-LUMO with 95% contribution, is

assigned to a π–π* transition.

It can be seen from the plots that the HOMO levels are spread over the entire

molecule expect the CH2 and CH3 groups in ground state and all positive and

negative phase are distributed unsymmetrical. The LUMO of first excited

state is almost uniformly distributed over the molecule without methyl and

methylene group, and all positive and negative phase are distributed

symmetrically.

The Molecular Electrostatic Potential analysis was carried out in this molecule

in order to explain its electron density surface, molecular size, shape as well as

positive, negative and neutral electrostatic potential regions in terms of colour

grading. The result of the analysis inferred that the negative potential sites are

on oxygen atoms as well as the positive potential sites are around the

hydrogen atoms.

Fig. 6.1. Molecular Structure with Conformers of Nicotinic Acid Ethyl Ester

Fig. 6.2. Potential Energy Scan of Nicotinic acid ethyl ester

1800

Conformer-1 Conformer-2

Fig. 6.3. Comparative Graph between experimental and theoretically calculated

bond lengths of Nicotinic Acid Ethyl Ester

Fig. 6.4. Experimental FT-IR Spectra of Nicotinic Acid Ethyl Ester

Fig. 6.5. Experimental FT-Raman Spectra of Nicotinic Acid Ethyl Ester

Ram

an

un

its

Fig.6.6. Correlation graph of heat capacity and temperature for NAEE molecule

Fig. 6.7. Correlation graph of entropy and temperature for NAEE molecule

Fig. 6.8. Correlation graph of enthalpy and temperature for NAEE molecule

Fig.6.9. The atomic orbital compositions of the frontier molecular orbital of

NAEE

LUMO

(First Excited State)

ELUMO= -2.00495 eV

EHOMO= -7.62142 eV

HOMO

(Ground State)

ΔE= 5.61647 eV

LUMO

(First Excited State)

ELUMO= -2.00495 eV

EHOMO-1= -7.75449 eV

HOMO-1

ΔE= 5.74954 eV

Fig. 6.10. Molecular electrostatic potential (MEP) map in gas phase of NAEE

Table 6.1

Optimized Geometrical Parameters (Bond lengths, Bond Angles and selected Dihedral angles) of Nicotinic Acid Ethyl Ester

Parameters

HF B3LYP LSDA Exp.

Data 6-311

G(d,p)

6-311++

G(d,p)

6-311

G(d,p)

6-311++

G(d,p)

6-311

G(d,p)

6-311 ++

G(d,p)

Bond length (Å)

N1-C2 1.320 1.320 1.337 1.337 1.330 1.330 1.338a

N1-C6 1.319 1.319 1.334 1.335 1.326 1.327

C2-C3 1.386 1.386 1.394 1.395 1.388 1.389 1.393a

C2-H7 1.077 1.077 1.087 1.086 1.097 1.097

C3-C4 1.379 1.380 1.389 1.388 1.380 1.381 1.383c

C3-C8 1.074 1.074 1.083 1.083 1.093 1.093 1.082b

C4-C5 1.387 1.388 1.396 1.397 1.387 1.388 1.392a

C4-H9 1.074 1.074 1.083 1.083 1.095 1.095 1.082a

C5-C6 1.388 1.389 1.399 1.400 1.391 1.392 1.394a

C5-C11 1.489 1.489 1.491 1.492 1.470 1.470 1.490a

C6-H10 1.074 1.074 1.084 1.084 1.096 1.096 1.087a

C11-O12 1.186 1.187 1.209 1.210 1.210 1.211 1.211c

C11-O13 1.319 1.318 1.347 1.347 1.337 1.337

O13-C14 1.426 1.426 1.449 1.451 1.429 1.430

C14-C15 1.512 1.512 1.515 1.514 1.494 1.494

C14-H16 1.082 1.082 1.092 1.092 1.104 1.104

C14-H17 1.082 1.082 1.092 1.092 1.104 1.104

C15-H18 1.086 1.086 1.093 1.093 1.100 1.101

C15-H19 1.085 1.085 1.092 1.092 1.100 1.101

C15-H20 1.085 1.085 1.092 1.092 1.100 1.101

Bond Angle (in degree)

C2-N1-C6 117.81 117.87 117.39 117.51 117.44 117.53 116.9a

N1-C2-C3 123.82 123.77 123.75 123.65 123.84 123.75 123.0a

N1-C2-H7 116.02 116.08 115.91 115.98 115.96 116.02

C3-C2-H7 120.16 120.14 120.34 120.37 120.21 120.23

C2-C3-C4 118.08 118.10 118.42 118.46 118.34 118.38 118.7c

C2-C3-H8 120.46 120.44 120.34 120.31 120.28 120.25 120.8d

C4-C3-H8 121.45 121.45 121.24 121.23 121.38 121.36 121.4d

C3-C4-C5 118.70 118.70 118.67 118.68 118.45 118.47 118.4a

C3-C4-H9 121.78 121.68 122.16 122.00 123.20 123.00 120.5d

C5-C4-H9 119.52 119.61 119.16 119.32 118.35 118.53 120.8a

C4-C5-C6 118.24 118.21 118.31 118.28 118.76 118.71 118.5a

C4-C5-C11 118.54 119.02 118.61 118.77 118.30 118.48 122.3c

C6-C5-C11 122.82 122.76 123.08 122.95 122.94 122.80 118.7c

N1-C6-C5 123.34 123.33 123.46 123.41 123.18 123.16 123.3a

N1-C6-H10 116.57 116.54 116.63 116.56 117.42 117.34 116.0a

C5-C6-H10 120.09 120.12 119.91 120.03 119.40 119.50 118.4d

C5-C11-O12 123.39 123.32 124.00 123.96 124.30 124.28 121.7c

C5-C11-O13 112.92 113.00 112.32 112.40 112.27 112.33 115.2c

O12-C11-O13 123.69 123.68 123.68 123.64 123.43 123.39 123.2c

C11-O13-C14 117.70 117.92 116.23 116.52 114.63 114.92

O13-C14-C15 107.54 107.61 107.50 107.60 107.55 107.68

O13-C14-H16 108.85 108.79 108.59 108.47 108.47 108.40

O13-C14-H17 108.85 108.79 108.59 108.47 108.47 108.40

C15-C14-H16 111.76 111.76 112.18 112.18 112.78 112.71

C15-C14-H17 111.76 111.76 112.18 112.18 112.78 112.71

H16-C14-H17 108.02 108.07 107.69 107.84 106.66 106.81

C14-C15-H18 109.69 109.53 109.75 109.52 110.23 110.01

C14-C15-H19 110.79 110.90 110.94 111.09 110.94 111.10

C14-C15-H20 110.79 110.90 110.94 111.09 110.94 111.10

H18-C15-H19 108.48 108.43 108.32 108.26 108.17 108.08

H18-C15-H20 108.48 108.43 108.32 108.26 108.17 108.08

H19-C15-H20 108.53 108.57 108.47 108.53 108.35 108.37

Selected Dihedral Angles

N1-C2-C3-C4 0.0 0.0 0.0 0.0 0.0 0.0

N1-C6-C5-C4 0.0 0.0 0.0 0.0 0.0 0.0

C4-C5-C11-O12 0.0 0.0 0.0 0.0 0.0 0.0

C4-C5-C11-O13 180.0 180.0 180.0 180.0 180.0 180.0

C5-C11-C13-C14 180.0 180.0 180.0 180.0 180.0 180.0

O12-C11-O13-C14 0.0 0.0 0.0 0.0 0.0 0.0

C11-O13-C14-C15 180.0 180.0 180.0 180.0 180.0 180.0

a Ref. [34],

b Ref. [35],

c Ref. [32-33],

d Ref. [22 ]

Table 6.2

Experimental and Theoretical (HF, B3LYP, LSDA) level vibrational frequencies (cm-1

) with TED (%) of Nicotinic Acid Ethyl Ester

Sl.

No

Symm

etry

Experimental

frequency

HF B3LYP LSDA

Assignment (TED > 10%)

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

6-311

G(d,p)

6-311++

G(d,p)

6-311

G(d,p)

6-311++

G(d,p)

6-311

G(d,p)

6-311++

G(d,p)

FT-IR FT-R U Sa U S

b U S

c U S

d U S

e U S

f

1. A' 3110(w) 3372 3063 3370 3050 3203 3097 3202 3078 3126 3088 3125 3004 CH (98)

2. A' 3090(w) 3369 3061 3368 3049 3187 3081 3188 3065 3111 3072 3109 2989 CH (98)

3. A' 3070(w) 3353 3046 3352 3034 3185 3079 3186 3063 3090 3052 3090 2971 CH (100)

4. A' 3050(w) 3323 3019 3324 3009 3150 3045 3153 3031 3072 3034 3074 2955 CH (99)

5. A' 3020(w) 3272 2972 3271 2961 3116 3013 3116 2996 3069 3032 3067 2948 CH of CH3 (99)

6. A' 2990(s) 3242 2945 3240 2932 3106 3003 3104 2984 3068 3030 3066 2948 CH of CH3 (98)

7. A' 2980(s) 3238 2942 3238 2930 3087 2985 3089 2970 3013 2976 3014 2897 CH of CH2 (99)

8. A' 2940(w) 2940(s) 3218 2924 3217 2912 3053 2951 3054 2936 2983 2947 2982 2867 CH of CH2 (98)

9. A' 2900(w) 2900(w) 3174 2883 3173 2871 3038 2938 3037 2920 2975 2939 2975 2860 CH of CH3 (100)

10. A' 1720(s) 1720(s) 1969 1789 1952 1767 1782 1723 1766 1698 1782 1760 1769 1700 C11=O12 (90)

11. A' 1600(s) 1794 1630 1790 1621 1632 1578 1630 1567 1628 1608 1626 1564 C=C (55)

12. A' 1590(s) 1771 1609 1767 1599 1611 1558 1608 1546 1602 1582 1600 1538 C=C(56)

13. A' 1480(m) 1651 1500 1648 1492 1523 1472 1519 1461 1475 1457 1474 1417 CH2(86)

14. A' 1470(m) 1637 1488 1635 1480 1507 1457 1506 1448 1448 1431 1444 1388 C=N (89)

15. A' 1450(m) 1617 1469 1616 1463 1501 1451 1499 1441 1425 1407 1423 1368 CH3 (88)

16. A" 1420(s) 1601 1455 1602 1450 1487 1438 1487 1429 1424 1407 1422 1367 CH3 (88)

17. A' 1400(m) 1400(w) 1570 1426 1567 1419 1450 1402 1449 1393 1410 1393 1409 1355 C-C (96)

18. A' 1370(s) 1370(m) 1567 1424 1566 1417 1431 1383 1428 1373 1375 1358 1373 1320 CH3 (72)

19. A' 1330(s) 1523 1383 1522 1378 1401 1355 1400 1346 1365 1349 1365 1312 C14-C15(82)

20. A' 1290(s) 1290(s) 1467 1333 1467 1328 1355 1310 1355 1303 1333 1317 1331 1280 C-C (90)

21. A' 1260(w) 1445 1312 1442 1305 1304 1260 1302 1251 1294 1278 1294 1244 C-N (75)

22. A" 1250(w) 1416 1286 1416 1281 1297 1254 1297 1247 1284 1268 1284 1234 CH2 (84)

23. A' 1230(w) 1326 1205 1326 1200 1282 1239 1281 1231 1243 1228 1243 1195 C5-C11

24. A' 1200(m) 1200(m) 1287 1169 1285 1163 1222 1181 1221 1174 1191 1177 1191 1145 CH (78)

25. A" 1170(s) 1264 1148 1263 1143 1179 1140 1176 1131 1153 1139 1151 1107 CH2 (89)

26. A' 1110(m) 1110(m) 1253 1138 1252 1133 1149 1111 1147 1103 1130 1116 1127 1083 C11-O13 (58)

27. A' 1095(m) 1232 1120 1231 1114 1134 1096 1133 1089 1113 1099 1111 1068 CH (69)

28. A' 1050(m) 1181 1073 1182 1070 1131 1093 1130 1086 1090 1076 1091 1049 CH3(70)

29. A' 1040(s) 1142 1037 1140 1032 1061 1026 1060 1019 1056 1043 1054 1013 CH (84)

30. A' 1030(s) 1137 1033 1129 1022 1042 1007 1041 1000 1047 1034 1046 1006 CH (88)

31. A' 1020(m) 1120 1018 1117 1011 1035 1001 1033 993 1018 1005 1017 978 C15-C14 (45) + CO13 (24)

32. A" 980(vw) 1119 1017 1116 1010 1021 988 1012 973 986 974 974 937 CH (85)

33. A" 950(vw) 1118 1015 1113 1007 999 965 991 953 960 948 952 915 CH (88)

34. A" 940(vw) 1080 981 1071 969 965 933 958 921 929 918 922 887 CH (85)

35. A" 860(m) 968 879 966 874 891 861 888 853 893 882 891 857 CH3 (88)

36. A' 850(s) 947 860 945 855 868 839 866 832 858 847 856 823 OCO (40)+C14-O13(23)

+CC(18)

37. A" 820(m) 936 851 931 843 853 824 845 812 831 821 823 791 CH (89)

38. A" 790(w) 790(m) 876 796 875 792 814 787 814 782 776 766 776 746 CH3 (96)

39. A" 740(s) 843 766 842 762 754 729 753 724 734 725 732 704 OCCC (42)+ CCCH (25)

+COCO (16)

40. A' 705(s) 773 702 771 698 723 699 717 689 712 703 705 678 CCC (51)+ OCO (22)

+ CC(10)

41. A" 700(s) 771 700 763 690 719 695 715 687 707 698 704 676 CCNC (42)+ CCCH (37)

+CCCC (12)

42. A' 620(m) 620(s) 678 616 677 612 633 612 632 608 615 607 614 590 Ring def. CNC (47)

+ CCC (41)

43. A' 500(vw) 534 485 533 482 496 479 495 476 490 484 489 470 CCO (53)+ C11CC(18)

44. A" 420(vw) 488 443 482 437 446 431 440 423 430 424 424 408 CCNC (36)+ CCCC (32)

+CCCO (22)

45. A" 400(w) 450 409 445 403 402 389 396 381 388 383 387 372 CCNC (37)+ CCCH (23)

+CCCC (22)

46. A' 390(w) 422 383 421 381 392 379 390 375 378 373 371 357 CCO (40)+ OCO (20)

+ C11-C5 (14)

47. A' 330(s) 330(s) 354 322 354 320 330 319 330 317 332 328 331 319 CO13C (30)+ C11-C5 (21)

+ O13-C (16)

48. A' 260(s) 288 262 286 259 265 256 262 252 264 260 260 250 C11CC (44)+ COC (36)

+ CCO (18)

49. A" 200(s) 285 259 284 257 264 255 261 251 256 253 255 245 C-CH3 (94)

50. A" 190(s) 206 188 204 185 190 183 186 179 188 185 185 178 Ring (48)+ COCO (26)

+ OCCH (12)

51. A' 118 107 117 106 111 107 110 106 108 107 107 103 CCO (38)+ COC (30)

+ C11CC (24)

52. A" 108 98 107 97 100 96 98 94 101 100 99 96 CO13CC (55)+O12CCC

(25) + Ring (25)

53. A" 90 82 89 81 75 73 75 72 76 75 74 71 OCCC(32)+HC14O13C(37)

+CCO13C(30)

54. A" 48 43 46 42 44 43 43 41 46 45 46 44 OCCC(65)+HC14O13C(16)

+CCO13C (15)

a,b,c,d,e,f Wavenumbers scaled by the scaling factor of 0.9085; 0.9051; 0.9668; 0.9614; 0.9877; 0.9614

U-Unscaled theoretical frequency ; S-Scaled theoretical frequency; in-plane-bending; : out-of-plane bending; wagging; t:

twisting; : torsion; Ring def.: Ring deformation.

Table 6.3

Mean deviation, Mean absolute deviation, Standard deviation, Root Mean Square and correlation coefficient (between the calculated

and observed fundamental vibrational frequencies of Nicotinic Acid Ethyl Ester

Parameter

HF B3LYP LSDA

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

U S U S U S U S U S U S

Mean Deviation 78.5 31.2 141.7 31.2 49.4 22.7 47.4 22.4 26.4 21.8 25.6 47.7

Mean Absolute Deviation 64.4 20.2 64.5 20.5 32.6 19.2 33.3 16.9 21.5 17.9 21.4 28.7

RMS 164.6 48.7 162.6 49.4 66.7 44.3 65.8 46.8 50.2 48.8 50.2 70.9

0.9986 0.9987 0.9988 0.9988 0.9985 0.9985

U – Unscaled calculated frequency Vs Experimental frequency; S – Scaled calculated frequency Vs Experimental frequency

Experimental frequency and Scaled calculated frequency

Table 6.4

Theoretically computed Zero point vibrational energy (kcal mol-1

), rotational constants (GHz), thermal energy (kcal mol-1

), molar

capacity at constant volume (cal mol-1

Kelvin-1

), entropy (cal mol-1

Kelvin-1

) and dipole moment (Debye)

Parameter

HF B3LYP LSDA

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

ZPVE 107.26125 107.08532 100.06211 99.88895 97.85467 97.67361

Rotational Constants

A 2.80467 2.80016 2.76299 2.75702 2.82213 2.81585

B 0.62432 0.62381 0.61325 0.61270 0.62503 0.62459

C 0.51388 0.51338 0.50502 0.50446 0.51502 0.51451

Energy 113.172 113.027 106.350 106.206 104.234 104.082

Molar capacity at constant

volume 33.834 33.937 36.433 36.566 37.193 37.331

Entropy 97.500 97.693 100.094 100.373 100.455 100.693

Dipole moment 0.4225 0.4871 0.5957 0.6472 0.6652 0.6964

Table 6.5

Thermodynamic properties at different temperatures at the

B3LYP/6-311++G(d,p) level for Nicotinic Acid Ethyl Ester

T(K) C0

p,m (calmol-1

K-1

) S0

m (calmol-1

K-1

) ∆H0

m (calmol-1

K-1

)

100 16.607 71.453 1.316

150 21.325 79.891 2.364

200 26.111 87.246 3.648

250 31.286 94.064 5.181

298.15 36.566 100.373 6.909

300 36.771 100.613 6.981

350 42.305 107.004 9.057

400 47.647 113.270 11.407

450 52.643 119.409 14.015

500 57.228 125.405 16.863

550 61.391 131.248 19.930

600 65.158 136.927 23.195

650 68.564 142.438 26.638

700 71.651 147.781 30.244

Table 6.6

Calculated energies values of Nicotinic acid ethyl ester in Gas and solvent

(DMSO and chloroform) phase

TD-DFT/B3LYP

/6-311++G(d,p) DMSO Chloroform Gas

Etotal (Hartree) -515.47287617 -515.47220635 -515.47007896

EHOMO (eV) -7.38468 -7.55013 -7.62142

ELUMO (eV) -1.91760 -1.97828 -2.00495

EHOMO-LUMO gap (eV) 5.46708 5.57185 5.61647

EHOMO-1 (eV) -7.70905 -7.74061 -7.75449

ELUMO+1 (eV) -1.20820 -1.26099 -1.28493

EHOMO-1-LUMO+1 gap (eV) 6.50085 6.47963 6.46956

Dipole moment (Debye) 0.6695 0.6611 0.6472

Table 6.7

Theoretical electronic absorption spectra of Nicotinic acid ethyl ester (absorption wavelength λ (nm), excitation energies E (eV) and

oscillator strengths ( f )) using TD-DFT/B3LYP/6-311++G(d,p) method in gas and solvent (DMSO and chloroform) phase.

DMSO Chloroform Gas Gas

Assignment

λ (nm) E (eV) ( f ) λ (nm) E (eV) ( f ) λ (nm) E (eV) ( f ) Major contributiona

280.93 4.4134 0.0007 283.90 4.3672 0.0007 290.97 4.2611 0.0006 H-1 L (95%)

247.52 5.0091 0.0039 249.84 4.9625 0.0039 255.15 4.8592 0.0032 L (95%)

245.87 5.0427 0.0002 247.57 5.0080 0.0001 251.45 4.9309 0.0000 H-4 L (93%)

a H: Humo, L: Lumo