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(This is a sample cover image for this issue. The actual cover is not yet available at this time.)
This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institution
and sharing with colleagues.
Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies areencouraged to visit:
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy
j our na l ho me p age: www.elsev ier .com/ locate /saa
Spectroscopic analysis (FT-IR/FT-Raman) and molecular structure investigationon m-fluoronitrobenzene using hybrid computational calculations
S. Ramalingama,∗, M. Karabacakb, S. Periandyc, N. Puviarasand
a Department of Physics, A.V.C. College, Mayiladuthurai, Tamilnadu, Indiab Department of Physics, Afyon Kocatepe University, Afyonkarahisar, Turkeyc Department of Physics, Tagore Arts college, Puducherry, Indiad Satellite Meteorology Division, Ministry of Earth Sciences, Lodi Road, New Delhi, India
a r t i c l e i n f o
Article history:Received 20 January 2012Received in revised form 4 March 2012Accepted 10 March 2012
Keywords:m-FluoronitrobenzeneMolecular electrostatic potentialVibrational patternPedestal moleculeFrontier molecular orbital energiesMulliken charges
a b s t r a c t
In the present investigation, the FT-IR/FT-Raman spectra of the m-fluoronitrobenzene (m-FNBZ) arerecorded. The fundamental frequencies are assigned and the computational calculations are performedby DFT (B3LYP, B3PW91 and MPW1PW91) methods with 6−31++G(d,p) and 6−311++G(d,p) basis setsand the corresponding results are tabulated. The computed values of frequencies are scaled by usingsuitable factors. The distortion of the structure of the compound due to the substitutions of Fl and NO2
is investigated. The alternation of the vibrational pattern of the pedestal molecule related to the sub-stitutions is analyzed. A study on the electronic properties; absorption wavelengths, excitation energy,dipole moment and frontier molecular orbital energies, are performed by time dependent DFT (TD-DFT)approach. The electronic structure and the assignment of the absorption bands in the electronic spectraof steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transferoccurs within the molecule. Besides frontier molecular orbitals (FMO), molecular electrostatic potential(MEP) was performed. Mulliken charges of the m-FNBZ molecule was also calculated and interpreted.The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at differenttemperatures were calculated in gas phase.
Aromatic compound such as benzene derivative of fluoroni-trobenzene is commonly used in pharmaceutical products. Benzeneundergoes nitration and halogenations, then the reactions of thebenzene slow down. Nitrofluorobenzene are produced for indus-trial uses such as dyes, drugs, pesticides, shoe polish, spray paint,and synthetic rubber [1,2]. Fluorine substituent can greatly increasethe fat solubility of molecules, which is particularly importantin pharmaceuticals where it can increase their bioavailability.Molecules including more fluorine, amplifies the effect and haveregular feature in both drug and agrochemical actives. Numerouscommon fungicides also contain fluorine atoms. Fluorine is a com-mon element in antibiotic molecules, too. Fluorine has become apopular feature in drugs and agrochemicals because of the effectsit exerts in molecules. The anti-inflammatory drugs are designedto treat rheumatoid arthritis [1].
Fluorine is the most electronegative atom of all the compounds.It pulls electrons toward it, thus reducing the electron density at the
carbon in a C F bond. It also affects the molecule’s dipole momentand the molecule’s overall stability. Nitrobenzene is an aromaticnitro compound. Most nitrobenzene (97%) is used in the manufac-turing of aniline. Nitrobenzene is highly toxic in large quantitiesand is mainly produced as a precursor to aniline. In the laboratoryit finds occasional use as a solvent especially for electrophilic [2].
Nitrobenzene can cause a wide variety of harmful health effectsto exposed persons. Repeated exposures to a high concentrationof nitrobenzene can result in a blood condition called methe-moglobinemia (a form of anemia). This condition affects theability of blood carrying oxygen [3]. Exposure level is extremelyhigh nitrobenzene can cause coma and possibly death unlessprompt medical treatment is received. In case of long-term expo-sure to nitrobenzene, the presence of its breakdown products,p-nitrophenol and p-aminophenol, in the urine is an indication ofnitrobenzene exposure. The results of these tests cannot be used todetermine the level of nitrobenzene exposure [4,5]. Therefore thefluorine substituted nitrobenzene is also used to produce pharma-ceutical drugs and agrochemical products.
Various spectroscopic studies of halogen substituted com-pounds have been reported in the literature [6–12] so far. Themolecular structure of ortho- and para-fluoronitrobenzene havebeen investigated by HF and DFT calculations [13,14]. However,
Table 1Optimized geometrical parameters for m-fluoronitrobenzene computed at B3LYP, B3PW91 and MPW1PW91 methods, 6−31++G(d,p) and 6−311++G(d,p) basis sets.
320 S. Ramalingam et al. / Spectrochimica Acta Part A 94 (2012) 318– 330
Tabl
e
1
(Con
tinu
ed)
Geo
met
rica
l par
amet
ers
Met
hod
s
B3L
YP/
6−31
++G
(d,p
)
B3L
YP/
6−31
1++G
(d,p
)
B3P
W91
/6−3
1++G
(d,p
)
B3P
W91
/6−3
11++
G(d
,p)
MPW
1PW
91/6
−31+
+G(d
,p)
MPW
1PW
91/6
−311
++G
(d,p
)
H8
C4
C3
C2
180.
0
180.
0
180.
0
180.
0
180.
0
180.
0H
8C
4C
3N
100.
0
0.0
0.0
0.0
0.0
0.0
C4
C3
C2
C1
0.0
0.0
0.0
0.0
0.0
0.0
C4
C3
C2
H9
180.
0
180.
0
180.
0
180.
0
180.
0
180.
0N
10C
3C
2C
118
0.0
180.
0
180.
0
180.
0
180.
0
180.
0N
10C
3C
2H
90.
0
0.0
0.0
0.0
0.0
0.0
C4
C3
N10
O11
180.
0
180.
0
180.
0
180.
0
180.
0
180.
0C
4C
3N
10O
120.
0
0.0
0.0
0.0
0.0
0.0
C2
C3
N10
O11
0.0
0.0
0.0
0.0
0.0
0.0
C2
C3
N10
O12
180.
0
180.
0
180.
0
180.
0
180.
0
180.
0C
3C
2C
6C
10.
0
0.0
0.0
0.0
0.0
0.0
C3
C2
C1
F 13
180.
0
180.
0
180.
0
180.
0
180.
0
180.
0H
9C
2C
1C
618
0.0
180.
0
180.
0
180.
0
180.
0
180.
0H
9C
2C
1F 1
30.
0
0.0
0.0
0.0
0.0
0.0
no HOMO–LUMO, MEP, NLO analysis or DFT calculation withB3LYP/B3PW91/MPW1PW91 methods at 6−31++G(d,p) and6−311++G(d,p) basis sets is reported on m-FNBZ so far, in spiteof its pharmaceutical importance. Hence, in the present work adetailed DFT vibrational, NLO and electronic structure analysis hasbeen attempted by recording FT-IR and FT-Raman spectra of thecompound m-FNBZ, considering its biological and pharmaceuticaluses.
2. Experimental details
The compound m-FNBZ is purchased from Sigma–AldrichChemicals, USA, which is of spectroscopic grade and hence usedfor recording the spectra as such without any further purification.The FT-IR spectrum of the compound is recorded in Bruker IFS 66Vspectrometer in the range of 4000–400 cm−1. The spectral reso-lution is ±2 cm−1. The FT-Raman spectrum of same compound isalso recorded in the same instrument with FRA 106 Raman mod-ule equipped with Nd:YAG laser source operating at 1.064 �m linewidths with 200 mW power. The spectra are recorded in the rangeof 4000–100 cm−1 with scanning speed of 30 cm−1 min−1 of spec-tral width 2 cm−1. The frequencies of all sharp bands are accurateto ±1 cm−1.
3. Computational methods
In the present work, some of the hybrid methods such asB3LYP, B3PW91 and MPW1PW91 were carried out using thebasis sets 6−31++G(d,p) and 6−311++G(d,p). All these calcu-lations are performed using GAUSSIAN 09 W program packageon Pentium IV processor in personal computer. In DFT meth-ods; Becke’s three parameter hybrids function combined withthe Lee–Yang–Parr correlation function (B3LYP) [15,16], Becke’sthree parameter exact exchange-function (B3) [17] combined withgradient-corrected correlational functional of Lee, Yang and Parr(LYP) [18,19] and Perdew and Wang (PW91) [20,21] predict thebest results for molecular geometry and vibrational frequencies formoderately larger molecules. Modified Perdew–Wang exchangeand Perdew–Wang 91 correlation method (MPW1PW91) are thebest predicting results for molecular geometry and vibrationalwave numbers for moderately larger molecule [22,23]. The opti-mized structural parameters are used in the vibrational frequencycalculations at DFT (B3LYP, B3PW91 and MPW1PW91) levels. Theminimum energy of geometrical structure is obtained by usinglevel 6−31++G(d,p) and 6−311++G(d,p) basis sets. At the opti-mized geometry for the title molecule no imaginary frequencymodes are obtained, so there is a true minimum on the poten-tial energy surface is found. The calculated frequencies are scaledby 0.952, 0.932, 1.02, 0.940 and 1.2 for B3LYP/6−31++G(d,p). For6−311++G(d,p) basis set is scaled by 0.958, 0.938, 1.03 and 1.2.For B3PW91/6−31++G(d,p) set is scaled by 0.950, 0.910, 1.04, 1.2and 0.930. For 6−311++G(d,p) basis set is scaled by 0.956, 0.926,0.905 and 1.02. For MPW1PW91/6−31++G(d,p) basis set is scaledby 0.944, 0.930, 0.896, 1.04 and 0.920. For 6−311++ G(d,p) basisset is scaled by 0.950, 0.920, 1.02 and 0.930. The comparative opti-mized structural parameters such as bond length, bond angle anddihedral angle are presented in Table 1.
The total energy distribution (TED) calculations show the rel-ative contributions of the redundant internal coordinates to eachnormal vibrational mode of the molecule which enable numericallyto describe the character of each mode and are carried out by SQMmethod [24,25] using the output files created at the end of the fre-quency calculations. The TED calculations are performed by usingPQS program [25].
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Fig. 1. Molecular structure of m-fluoronitrobenzene.
The electronic properties, such as HOMO–LUMO energies,absorption wavelengths and oscillator strengths are calculatedusing B3LYP method of the time-dependent DFT (TD-DFT) [26,27],basing on the optimized structure in solvent (DMSO and chlo-roform) and gas phase. Thermodynamic properties of the titlecompound at different temperatures have been calculated in gasphase using B3LYP/6−311++G(d,p) method.
4. Results and discussion
4.1. Molecular geometry and potential energy surface scan
The molecular structure of m-FNBZ belongs to C2V pointgroup symmetry. The optimized molecular structure of themolecule is obtained from Gaussian 09 and Gauss view pro-gram [28] and is shown in Fig. 1. The molecule contain Fland NO2 group connected with benzene ring. The struc-ture optimization and zero point vibrational energy of thecompound in B3LYP/6−31++G(d,p), B3LYP/6−311++G(d,p),B3PW91/6−31++G(d,p), B3PW91/6−311++G(d,p),MPW1PW91/6−31++G(d,p) and MPW1PW91/6−311+G(d,p)are 59.41, 59.09, 59.72, 59.40, 60.19 and 59.87 Kcal/Mol respec-tively. The comparative optimized structural parameters such asbond lengths, bond angles and dihedral angles are presented inTable 1. Experimental and simulated spectra of IR and Raman arepresented in Figs. 2 and 3 respectively.
The breaking of the pedestal structure belongs to one planesince the substitutions of the nitro group and halogen F arein the same plane of benzene ring. The bond length betweenC C of right moiety of the benzene ring is reduced whereasthe bond length of the left moiety is stretched out. Particu-larly the bond length stretching is greater at the place of NO2group than F atom. It is also evident from the bond length orderas C1 C2 < C1 C6 < C3 C4 < C2 C3 < C4 C5 < C5 C6. The C F bondlength indicates a considerable increase when substituted in placeof C H. Therefore, the coherent of F atom at C which shares its �electron with the ring leads to some changes of the bond lengthsand bond angles of the aromatic ring. The N12 O13 and N12 O14bond lengths are equal as compared to those bond lengths ofnitro benzene [29]. The C F bond length value is calculated as1.338–1.354 A which is in good agreement with literature [13].
Fig. 2. Experimental [A], calculated [B], [C] and [D] FT-IR spectra of m-fluoronitrobenzene.
The hexagonal structure of the ring is mutilated by thesubstitutions and is proved by the bond angle order asC1 C2 C3 < C3 C4 C5 < C5 C6 C1 < C4 C5 C6 < C2 C1 C6 < C2C3 C4. The bond angle 122.8◦ at the place of the NO2 group in thering is 0.3◦ elongated than the place of F. The rest of the bond anglesof the ring are less. The bond angle between the substitutions isgreatly reduced to 116.9◦.
Substitution with the F atom and NO2 group leads to somechanges of the bond angles in the benzene ring. The C2 C3 C4and C2 C3 C4 angles at the position of the F atom NO2 group sub-stituent is bigger (122◦) and the others are smaller or equal typicalhexagonal angle of 120◦. This clearly shows that the substitution ofF atom and NO2 group in place of hydrogen appreciably affects theC2 C3 C4 and C2 C3 C4 bond angles.
Fig. 3. Experimental [A], calculated [B], [C] and [D] FT-IR spectra of m-fluoronitrobenzene.
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Fig. 4. PES scan for the selected torsional angle T(C C N O) of freedom.
To determine the most stable energy conformation of the m-FNBZ molecule, a conformation analysis is performed betweenbenzene ring and NO2 group system on C C N O atoms. Toexplain conformational features of m-FNBZ, the selected degreeof torsional freedom, T(C C N O) was varied from 0◦ to 360◦ invery 10◦ and the molecular energy profile is obtained with theB3LYP/6−311++G(d,p) method. The conformational energy profileshows two maxima near 90◦ and 270◦ title torsion angle. The maxi-mum energies are obtained −536.131739795 and −536.131739946Hartree for 90◦ and 270◦ dihedral angles, respectively. The aromaticrings are nearly perpendicular at these values of selected torsionangle. It is clear from Fig. 4, there are two local minima observed at0◦ (or 360◦) and 180◦ for the torsion angle. The minimum energyis obtained −536.140708626 Hartree. From this result, it is foundthat, the NO2 group is at same plane with the ring.
4.2. Vibrational assignments
The m-FNBZ molecule consists of 14 atoms, which undergoes36 normal modes of vibrations. On the assumption of C2v group ofsymmetry, the numbers of vibration modes of the 36 fundamentalvibrations of the molecule are distributed as
�Vib. = 13A1 + 7B1 + 4A2 + 12B2
The assignments are shown in Table 2. The harmonic vibrationalfrequencies (unscaled and scaled) calculated at B3LYP, B3PW91 andMPW1PW91 levels using the triple split valence basis set alongwith the diffuse and polarization functions, 6−31++G(d,p) and6−311++G(d,p) and observed FT-IR and FT-Raman frequencies forvarious modes of vibrations have been presented in Tables 3 and 4.Comparison of frequencies calculated at HF and B3LYP/LSDA withthe experimental values reveal the over estimation of the calcu-lated vibrational modes due to the neglect of a harmonicity in realsystem. Inclusion of electron correlation in the density functionaltheory to certain extends makes the frequency values smaller incomparison with the HF frequency data. Therefore, we selectedDFT/B3LYP/B3PW91/MPW1PW91 levels. Reduction in the com-puted harmonic vibrations, although basis set sensitive is onlymarginal as observed in the DFT values using 6−311++G(d,p). Thecalculated IR intensity and Raman activity values are presented inTables 5 and 6, respectively.
4.2.1. Computed vibrational frequency analysisThe standard deviation (SD) calculation made between
experimental and computed frequencies DFT for the m-FNBZ ispresented in Table 7. According to the SD, the computed frequencydeviation decreases in going from MPW1PW91/6−31++G(d,p)
Table 2Experimental FT-IR, FT-Raman frequencies (cm−1) and assignments for m-FNBZ.
Species C2v FT-IR (cm−1) FT-Raman (cm−1) Vibrational Assignments
A1 3100 s – (C H) �B2 3095 s – (C H) �B2 3090 s 3090 m (C H) �A1 3050 w – (C H) �B2 1590 vs 1590 m (C C) �A1 1530 vs – (C C) �B2 1500 vs 1500w (NO2) � asymA1 1370 vs – (C C) �B2 1350 vs 1350 vs (NO2) � symA1 1345 vs – (C C) �B2 1320 s 1320 m (C C) �B2 1200 vs – (C C) �A1 1140 vs 1140 w (C F) �A1 1100 vs 1100 s (C H) ıA1 1090 vs – (C H) ıB2 1060 w – (C H) ıA1 1020 m – (C H) ıA2 1005 w – (C N) � (C H) �B1 1000 m – (C H) �A1 870 vs 870 s (C H) �B1 860 w – (C H) �A2 820 w 820 w (CCC) ıA1 810 w 810 w (CCC) ıB1 760 vs – (NO2) ıB1 720 vs – (CCC) ıB2 620 vs – (C N) ıA1 570 w – (NO2) ωB2 560 w – (NO2) ıB1 480 m – (CCC) �A2 450 m – (CCC) �B2 420 m – (CCC) �A1 – 320 w (C F) ıB1 – 305 m (C N) �B2 – 250 w (C F) �B1 – 170 w (NO2) �A2 – 110 w (NO2) �
vs – very strong; s – strong; m – medium; w – weak; � – stretching; ı – in planebending; � – out plane bending; � – twisting.
to MPW1PW91/6−311++G(d,p) to B3LYP/6−31++G(d,p)to B3PW91/6−31++G(d,p) to B3PW91/6−311++G(d,p) toB3LYP/6−311++G(d,p). The deviation ratio between B3LYPmethods is 1.21, between B3PW91 methods is 1.06 and betweenMPW1PW91 methods is 1.05. It is also observed that the calculatedfrequencies by B3LYP/6−311++G(d,p) basis sets are closer to theexperimental frequencies.
4.2.2. C H vibrationsThe aromatic organic compounds structure; benzene and its
derivatives show the presence of asymmetric C H stretchingvibrations in the region 3100–3000 cm−1 [30–32] which is the char-acteristics region for recognition on C H stretching vibrations. Inthe title molecule, four bands have been observed at 3100, 3095,3090 and 3050 cm−1 assigned to C H stretching vibrations. Theentire vibrations are observed at the top end of the expected regionwhich is due to the favoring of the substitutions. All aromatic C Hstretch modes are pure stretching modes as it is evident from TEDcolumn in Table 4, they are almost 100%. This is indicating that theimpact of substitution NO2 group in the molecule which does notmuch influence the vibration of aromatic C H.
The strongest absorptions for aromatic compounds occur in theregion 1300–1000 cm−1 and 1000–750 cm−1 due to the C H inplane and out of plane bending vibrations respectively [33–37]. Inthe present case, the in plane bending vibrations are found at 1100,1090, 1060 and 1020 cm−1 in FT-IR and FT-Raman. The out of planebending vibrations are observed at 1005, 1000, 870 and 860 cm−1.Most of the bending vibrations are found in IR and all the bend-ing vibrations are within the expected region. This view indicates
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Table 3Calculated with B3LYP/B3PW91/MPW1PW91 methods at 6−31++G(d,p) and 6−311++G(d,p) level unscaled vibrational frequencies (cm−1) of m-FNBZ.
that the substitutions in the ring have not influenced the bendingvibrations.
4.2.3. C C vibrationsThe ring stretching vibrations are very much important in the
spectrum of benzene and its derivatives are highly characteris-tic of the aromatic ring itself. The ring C C and C C stretchingvibrations, known as semicircle stretching usually occur in theregion 1400–1625 cm−1 [33]. Particularly, the bands between theregions 1590–1650 cm−1 [38] and 1590–1430 cm−1 [39,40] in ben-zene derivatives are usually assigned to C C and the C C stretchingvibrations respectively. In the present case, the C C stretchingvibrations are observed with very strong intensity at 1590, 1530and 1370 cm−1. The corresponding C C stretching vibrations arefound with very strong intensity at 1345, 1320 and 1200 cm−1.Except one in C C, the entire vibrations are observed well belowthe expected region. From this observation it is clear that the ringstretching vibrations are affected much due to the NO2 and F.
In the present compound, the C C C in-plane and out of planebending vibrations are appeared very strong and medium intensityat 820, 810 and 720 cm−1 and 480, 460 and 420 cm−1 respectively.All the assignments related to in-plane and out of plane bendingvibrations are in coherent with the literature values [6,8,10,33–35].
4.2.4. NO2 vibrationsThe asymmetric stretching for the NO2 has a magnitude higher
than that of the symmetric stretching [41]. The characteristic groupfrequencies of the nitro group are relatively independent of therest of the molecule which makes this group convenient to iden-tify. Aromatic nitro compounds have strong absorptions due to the
asymmetric and symmetric stretching vibrations of the NO2 groupat 1570–1485 cm−1 and 1370–1320 cm−1 respectively [38]. Asiriet al. [42] assigned the frequencies at 1512 and 1332 cm−1 to NO2asymmetric and symmetric stretching vibrations, respectively. Inthis present case, two very strong bands at 1500 and 1350 cm−1
have been assigned to asymmetric and symmetric stretching modesof NO2 respectively. The TED of these modes are contributing 80%for NO2 asymmetric stretching and 80% for NO2 symmetric stretch-ing. Because of the favoring of other substitutions in the ring, boththe vibrations are found well above the expected range.
The other vibrations of NO2 group (rocking, wagging and twist-ing) contribute to several normal modes in the low frequencyregion. Aromatic nitro compounds have a band of weak to mediumintensity in the region 590–500 cm−1 [33] due to the out-of-planebending deformation mode of the NO2 group. Likewise, the in-planeNO2 deformation vibrations have a week to medium absorption inthe region 775–660 cm−1 [33]. The deformation (in-plane bend-ing) is observed at 760 cm−1 [43] and out-plane bending vibrationis assigned at 570 cm−1. The NO2 twisting for this compound is at170 and 110 cm−1 in FT-Raman spectrum. Thus the NO2 vibrationshave not affected by the substitutions in the ring.
4.2.5. C F vibrationsAssignments of the C F stretching modes are very difficult
as these vibrations are strongly coupled with the other in planebending vibrations of several modes. The observed bands of theC F stretching vibrations have been found to be very strong inthe IR spectra and these appear in the range 1000–1300 cm−1 forseveral fluoro-benzenes [44,45]. And also the C F stretching vibra-tions strongly coupled with the C H in-plane bending vibrations
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Table 4Calculated with B3LYP/B3PW91/MPW1PW91methods at 6−31++G(d,p) and 6−311++G(d,p) level scaled frequencies (cm−1) of m-FNBZ.
in the mono fluorinated benzene and is observed in the region1100–1000 cm−1 [46]. In the present case, the C F stretching vibra-tion is observed at 1140 cm−1. The C F in-plane bending vibrationmode for the mono fluorinated benzene is normally assigned at250–350 cm−1 [47]. In the present case, a band is assigned to C F in-plane bending at 320 cm−1. The frequency of the C F out-of-planebending vibration assigned at 250 cm−1. According to the reportedvalues [48], this assignment is in line with the literature. All theC F vibrations are found within the expected region which showsthat these vibrations have not affected by other substitution in thering.
4.2.6. C N vibrationsThe identification of C N vibrations is difficult task since the
mixing of vibrations is possible in this region. Mostly, the ring C Hbending vibrations are mixed with this vibration. In this presentmolecule, the C N stretching vibration is identified with weakintensity at 1005 cm−1 in infrared region and is mixed with theC H out of plane bending vibration. The corresponding C N in-plane and out-of-plane bending vibrations are found at 620 and305 cm−1. This view is supported by the literatures [14,35].
4.3. Thermodynamic properties
The variation in Zero-Point Vibrational Energies (ZPVEs)seems to be significant. The values of some thermodynamicparameters (such as zero-point vibrational energy, thermalenergy, specific heat capacity, rotational constants, entropy, anddipole moment) of m-FNBZ by DFT (B3LYP/B3PW91/MPW1PW91)with 6−31++G(d,p)/6−311++G(d,p) method at 298.150 K and
1.00 atm pressure are listed in Table 8. The ZPVE energy ismuch lower in the DFT/B3LYP method [for 59.09892 kcal mol−1
B3LYP/6−311++G(d,p)] than by other methods. The biggestvalue of ZPVE of m-FNBZ is 60.19197 kcal mol−1 obtained atMPW1PW91/6−31++G(d,p) method.
On the basis of vibrational analysis at B3LYP/6−311++G(d,p)level, the standard statistical thermodynamic functions: standardheat capacities (Cp,m
◦) standard entropies (Sp,m◦), and standard
enthalpy changes (Hm◦) for the title compound are obtained from
the theoretical harmonic frequencies and listed in Table 9.From Table 9, it can be observed that these thermodynamic
functions are increasing with temperature ranging from 100 to700 K due to the fact that the molecular vibrational intensitiesincrease with temperature. The correlation equations between heatcapacity, entropy, enthalpy changes and temperatures are fitted byquadratic formulas and the corresponding fitting factors (R2) forthese thermodynamic properties are 0.9992, 1.0000 and 0.9998,respectively. The corresponding fitting equations are as follows andthe correlation graphics of those shows in Figs. 5–7.
All the thermodynamic data supply helpful information for thefurther study on the m-FNBZ. They can be used to compute the otherthermodynamic energies according to relationships of thermo-dynamic functions and estimate directions of chemical reactionsaccording to the second law of thermodynamics in thermochemical
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326 S. Ramalingam et al. / Spectrochimica Acta Part A 94 (2012) 318– 330
Table 6Comparative values of Raman activities between B3LYP/B3PW91/MPW1PW91 at 6−31++G(d,p) and 6−311++G(d,p) basis sets of m-FNBZ.
field. Notice: all the thermodynamic calculations have been carriedout in gas phase and they could not be used in solution.
4.4. Molecular electrostatic potential (MEP) maps
To predict reactive sites for electrophilic and nucleophilic attackfor the investigated molecule, MEP is calculated (red is negative,blue is positive) at the B3LYP/6−311++G(d) optimized geometries.Fig. 8 shows the calculated 3D electrostatic potential contour mapof m-FNBZ. The negative regions of V(r) were related to elec-trophilic reactivity and the positive ones to nucleophilic reactivity.The different values of the electrostatic potential at the surface arerepresented by different colors. Potential increases in the orderred < orange < yellow < green < blue. The color code of these mapsis in the range between −0.04315 a.u. (deepest red) to 0.04315 a.u.(deepest blue) in compound, where blue indicates the strongestattraction and red indicates the strongest repulsion. As easily canbe seen in Fig. 8, this molecule has several possible sites for elec-trophilic attack in which V(r) calculations have provided insights.
The most negative V(r) value is associated with oxygen atomswith a value around −0.0430102 a.u. while the most positive valuecorrespond to the hydrogen atoms of m-FNBZ molecule (about0.0380617 a.u.). From this result, it is clear that the H atoms indi-cate the strongest attraction and O atoms indicate the strongestrepulsion.
4.5. Mulliken atomic charge
The charge distribution on the molecule has an important influ-ence on the vibrational spectra. The calculated Mulliken chargedistributions of benzene derivates are compared in Table 10. Theresults show that substitution of the aromatic ring by NO2 groupand fluoro atom leads to a redistribution of electron density. Thecorresponding Mulliken’s plot is shown in Fig. 9 and illustration ofatomic charges plotted is shown in Fig. 10. The results show thatsubstitution of the aromatic ring by a F atom leads to a redistri-bution of electron density of benzene. As can be seen in Table 10all the hydrogen atoms have a net positive charge. Moreover, for
Table 7Standard Deviation of frequencies by DFT (B3LYP, B3PW91 and MPW1PW91) at 6−31++G(d,p) and 6−311++G(d,p) basis sets.
S. no. Basic set levels Total values Average Standard deviation Deviation ratio
Fig. 5. Correlation graphic of heat capacity and temperature for m-FNBZ molecule.
F-benzene molecule, the H9 and H14 atoms in cis position to Fatom accommodate higher positive charge than the other hydro-gen atoms. For nitrobenzene, the H8 and H9 atoms near position tooxygen atoms accommodate higher positive charge than the otherhydrogen atoms. Similar results can be seen for m-FNBZ. The Mul-liken atomic charge of m-FNBZ shows that the H9 atom has morepositive atomic charge [0.287e] than the other hydrogen atoms.This is due to the presence of electronegative flouro atom, thehydrogen atom attract the positive charge from the flouro atom.
Fig. 6. Correlation graphic of entropy and temperature for m-FNBZ molecule.
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328 S. Ramalingam et al. / Spectrochimica Acta Part A 94 (2012) 318– 330
Fig. 7. Correlation graphic of enthalpy and temperature for m-FNBZ molecule.
Fig. 8. Molecular electrostatic potential (MEP) map in gas phase of m-FNBZ.
4.6. Electronic properties (HOMO–LUMO analysis)
In order to understand electronic transitions of compound,time-dependent DFT (TD-DFT) calculations on electronic absorp-tion spectrum in vacuum and solvent (DMSO and Chloroform)are performed by B3LYP/6−311++G(d). The calculated absorptionwavelengths (), oscillator strengths (f), excitation energies (E)and dipole moments are given Table 11. The strong transitionsat 324.66 nm (3.8189 eV) with an oscillator strength f = 0.0346 in
Table 10Mulliken atomic charges of m-fluoronitrobenzene, fluoro benzene, nitrobenzeneand benzene using B3LYP/6−311++G(d,p) basis set.
Fig. 9. Mulliken charge distributions of m-FNBZ molecule.
DMSO, at 320.71 nm (3.8659 eV) in Chloroform and at 328.51 nm(3.7741 eV) in gas phase are assigned to a n–�* transition. Themajor contributions of the transitions are designated with the aidof SWizard program [49]. In view of calculated absorption spectra,the maximum absorption wavelength corresponds to the electronictransition from the HOMO−2 to LUMO with 97% contribution. Theother wavelength, excitation energies, oscillator strength and cal-culated counterparts with major contributions are presented inTable 11.
The highest occupied molecular orbital (HOMO) and lowestunoccupied molecular orbital (LUMO) are the main orbitals thattake part in chemical stability [50]. The HOMO represents the abilityto donate an electron, LUMO as an electron acceptor represents theability to obtain an electron the HOMO and LUMO energy calculatedby B3LYP with 6−311G++(d,p) basis set is shown in Fig. 11.
The HOMO is located over the benzene ring and F atom, theHOMO→LUMO transition implies an electron density transfer tonitro group from F atom. The HOMO could be characterized as a�-bonding molecular orbital and HOMO−2 could be characterizedas a n-bonding molecular orbital. Finally, the LUMO and LUMO+1exhibit a �-anti-bonding molecular orbital.
HOMO energy = −7.93708 eVLUMO energy = −3.15546 eV.HOMO–LUMO energy gap = 4.78162 eV.
Fig. 10. The graph of calculated Mulliken charge distributions of m-FNBZ.
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S. Ramalingam et al. / Spectrochimica Acta Part A 94 (2012) 318– 330 329
Table 11Theoretical electronic absorption spectra of m-FNBZ (absorption wavelength (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
(nm) E (eV) (f) (nm) E (eV) (f) (nm) E (eV) (f) Major contributiona Assignment
324.66 3.8189 0.0346 320.71 3.8659 0.0000 328.51 3.7741 0.0000 H-2 → L (97%) n–�*317.74 3.9020 0.0000 317.97 3.8992 0.0373 300.10 4.1314 0.0297 H → L (94%) �–�*281.39 4.4061 0.0003 283.62 4.3715 0.0003 289.16 4.2878 0.0003 H-3 → L (97%) �–�*
a H, HOMO; L, LUMO.
Table 12Calculated energies values of m-FNBZ in Gas and solvent (DMSO and chloroform) phase.
The energy gap explains the eventual charge transfer interac-tions taking place within the molecule. The increase in energy gapbetween HOMO and LUMO facilitates which makes the material tobe chemical hardness molecule. The value of chemical hardness is2.36081 eV for the title molecule
The dipole moment in a molecule is an important electronic fea-ture which results from non-uniform distribution of charges on thevarious atoms in a molecule. Based on predicted dipole momentvalues, it is found that, in going to the solvent phase from the gasphase, the dipole moment value increases (Table 12).
Fig. 11. The atomic orbital compositions of the frontier molecular orbital for m-FNBZ molecule in gas phase.
4.7. Polarizability first order hyperpolarizability calculations
In order to investigate the relationships among molecular struc-tures and non-linear optic properties (NLO), the polarizabilitiesand hyperpolarizabilities of title compound are calculated usingDFT-B3LYP method and 6−311++G(d,p) basis set, based on thefinite-field approach.
The polarizability and hyperpolarizability tensors (˛xx, ˛xy, ˛yy,˛xz, ˛yz, ˛zz and ˇxxx, ˇxxy, ˇxyy, ˇyyy, ˇxxz, ˇxyz, ˇyyz, ˇxzz, ˇyzz,ˇzzz) are obtained from frequency job output file of Gaussian. How-ever, and values of Gaussian output are in atomic units (a.u.)so the values have been converted into electronic units (esu) (˛;1 a.u. = 0.1482 × 10−24 esu, ˇ; 1 a.u. = 8.6393 × 10−33 esu). The meanpolarizability (˛), anisotropy of polarizability (�˛) and the aver-age value of the first hyperpolarizabiliy 〈ˇ〉 are calculated using theequations.
In Table 13, the calculated parameters described above and elec-tronic dipole moment {�i (i = x, y, z) and total dipole moment �tot}
Table 13The dipole moments � (Debye), the polarizability (a.u.), the average polarizability˛o (A), the anisotropy of the polarizability �˛ (A), and the component of hyperpo-larizability ˇx , ˇy and ˇz (a.u.) and the first hyperpolarizability (×10−30 cm5 esu−1)of m-FNBZ.
330 S. Ramalingam et al. / Spectrochimica Acta Part A 94 (2012) 318– 330
for title compound are listed. The total dipole moment can be cal-culated using the following equation.
�tot = (�x2 + �y
2 + �z2)
1/2
It is well known that the higher values of dipole moment, molec-ular polarizability, and hyperpolarizability are important for moreactive NLO properties.
The first order hyperpolarizability (ˇ) and the component ofhyperpolarizability ˇx, ˇy and ˇz of m-FNBZ along with relatedproperties (�0, ˛0, and �˛) are reported in Table 13. The calculatedvalue of dipole moment is found to be 1.652680 Debye. The high-est value of dipole moment is observed for component �x. In thisdirection, this value is equal to 1.326747 Debye. m-FNBZ has notgot �z component of dipole moment that value is zero. The calcu-lated polarizability and anisotropy of the polarizability of m-FNBZis 12.495957 × 10−23 esu and 29.968644 × 10−23 esu, respectively.The magnitude of the molecular hyperpolarizability ˇ, is one ofimportant key factors in a NLO system. The B3LYP/6−311++G(d,p)calculated first order hyperpolarizability value (ˇ) for the titlemolecule is equal to 3.6725256 × 10−30 esu. Total dipole momentof title molecule is approximately equal those of urea. The firstorder hyperpolarizability of title molecule is approximately fivetimes than those of urea (� and of urea are 1.525686 Debye and0.780324 × 10−30 esu obtained by B3LYP/6−311++G(d,p) method).
5. Conclusion
In the present work, the analyses have been made for vibrationalpattern of FT-IR and FT-Raman spectra, Total energy distribu-tion (TED), Zero-Point Vibrational Energies, Molecular electrostaticpotential (MEP) maps and Electronic properties of HOMO andLUMO. The fundamental frequencies are assigned and the com-putational calculations are performed by DFT (B3LYP, B3PW91and MPW1PW91) methods with 6−31++G(d,p) and 6−311++G(d,p)basis sets. The distortion of the structure of the compound due tothe substitutions of Fl and NO2 is discussed in detail. The Zero-PointVibrational Energies of the molecule are calculated and it is foundthat the ZPVE energy is much lower in the DFT/B3LYP method thanby other methods. The change of reactive sites for electrophilic andnucleophilic attack due to the substitutions is investigated from theMolecular Electrostatic Potential map. The first order hyperpolariz-ability (ˇ) and the component of hyperpolarizability are calculatedusing B3LYP/6−311++G(d,p) level and the importance related tothe NLO properties are discussed.
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