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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy
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olecular structure, polarizability, hyperpolarizability analysis and spectroscopicharacterization of 1-(chloromethyl)-2-methylnaphthalene with experimentalFT-IR and FT-Raman) techniques and quantum chemical calculations
.B. Nagabalasubramaniana,∗, M. Karabacakb, S. Periandyc
PRIST University, Vallam, Tanjavur, Tamilnadu, IndiaDepartment of Physics, Afyon Kocatepe University, 03040, Afyonkarahisar, TurkeyDepartment of Physics, Tagore Arts College, Puducherry, India
r t i c l e i n f o
rticle history:eceived 15 July 2011eceived in revised form 27 August 2011ccepted 1 September 2011
eywords:-(Chloromethyl)-2-methyl naphthaleneT-IR and FT-RamanOMO–LUMOF and B3LYP
a b s t r a c t
In this work, the FT-IR and FT-Raman spectrum of 1-(chloromethyl)-2-methyl naphthalene (abbrevi-ated as 1-ClM-2MN, C12H11Cl) have been recorded in the region 3600–10 cm−1. The optimum moleculargeometry, normal mode wavenumbers, infrared and Raman intensities, Raman scattering activities, cor-responding vibrational assignments, Mullikan atomic charges and thermo-dynamical parameters wereinvestigated with the help of HF and B3LYP (DFT) method using 6-311G(d,p), 6-311++G(d,p) basis sets.Also, the dipole moment, linear polarizabilities, anisotropy, first and second hyperpolarizabilities valueswere also computed using the same basis set. Reliable vibrational assignments were made on the basisof total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. The cor-relation equations between heat capacities, entropies, enthalpy changes and temperatures were fitted
LO by quadratic formulas. Lower value in the HOMO and LUMO energy gap explains the eventual chargetransfer interactions taking place within the molecule. UV–vis spectral analysis of 1-ClM-2MN has beenresearched by theoretical calculations. In order to understand the electronic transitions of the compound,TD–DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and chloroform)were performed. The calculated frontier orbital energies, absorption wavelengths (�), oscillator strengths(f) and excitation energies (E) for gas phase and solvent are also illustrated.
. Introduction
Naphthalene, a benzenoid polycyclic aromatic hydrocarbonPAH) has the structure of fused pair of benzene rings. PAHs can beroduced from both natural and human activities proved the clearvidence of the presence of PAHs in many astronomical objects1–3]. Recent research showed that the protonated cations of naph-halene are the source of part of the spectrum of the unidentifiednterstellar bands (UIBs) [4]. Naphthalene and its derivatives are
idely used as the chemical intermediate, wetting agent in manyndustrial applications, to study heat transfer with mass sublima-ion in engineering field, household fumigants such as mothballs,umigant pesticides. Exposure to large amounts of naphthalene
ay damage or destroy red blood cells and cause confusion, nausea,
omiting, diarrhea, blood in the urine, jaundice [5].
Several studies have been conducted on the vibrational spec-ra, electron exchange, structural stability, lattice vibrations, anti
resonance of naphthalene using normal co-ordinate analysis andresonance Raman spectral analysis [6–21]. Das et al. [22] stud-ied the infrared spectra of dimethylnaphthalenes in the gas phase.Librando and Alparone [23,24] investigated methyl naphthaleneisomers on quantum mechanical approach and the electronicpolarizability of dimethylnaphthalenes. 1-Methoxynapthalene wasstudied using FT-IR and FT-Raman spectra by Govindarajan et al.[6]. In our earlier study, we reported a scaled quantum mechani-cal vibrational analysis on 1,5-methylnaphthalene using FT-IR andFT-Raman spectra [25]. Vibrational absorption spectra, quasilineluminescence spectra of dimethylnaphthalene, vibrational spec-tra of methyl chloromethyl ether, Raman and infrared spectra of(choloromethyl) methyl sulfide, (chloromethyl) cyclopropane by abinitio calculations and Raman spectrum of chloromethyl thiocynatewere reported in the earlier literature [26–31].
To the best of our knowledge, neither quantum chemical cal-culations nor the vibrational spectra of 1-ClM-2MN have been
reported up to now. This inadequacy observed in the literatureencouraged us to do this theoretical and experimental vibrationalspectroscopic research to give a correct assignment of the funda-mental bands in the experimental FT-IR and FT-Raman spectra on
he basis of the calculated total energy distribution (TED). There-ore, the present study aims to give a complete description of the
olecular geometry, molecular vibrations and electronic featuresf the present molecule. Besides, frontier molecular orbitals (FMO)nd thermodynamic properties were performed. Thermodynamicroperties of the title compound at different temperatures haveeen calculated.
. Experimental details
The compound under investigation namely 1-ClM-2MN wasurchased from Aldrich Chemicals, U.S.A. which is of spectroscopicrade and hence used for recording the spectra as such with-ut any further purification. The FT-IR spectrum of the compoundas recorded in Brunker IFS 66V Spectrometer in the range of
600–10 cm−1. The spectral resolution is ±2 cm−1. The FT-Ramanpectrum of compound was also recorded in the same instru-ent with FRA 106 Raman module equipped with Nd:YAG laser
ource operating at 1.064 �m line width with 200 mW power. Thepectrum was recorded with scanning speed of 30 cm−1 min−1 ofpectral width 2 cm−1. The frequencies of all sharp bands are accu-ate to ±1 cm−1.
. Computational methods
The molecular structure optimization of the title compoundnd corresponding vibrational harmonic frequencies were calcu-ated using B3LPY exchange correlation functional [32,33] whichonsist of the Lee–Yang–Parr correlation functional in conjunctionith a hybrid exchange functional first proposed by Becke. Gaus-
ian 03 program package was used without any constraint on theeometry with the triple split valence basis set along with the dif-use and polarization functions; 6-311G(d,p) and 6-311++G(d,p).ED calculations were carried out by the scaled quantum mechan-cal (SQM) method [34] using PQS program [35]. Furthermore,rue rotational constants, IR and Raman intensity, Raman activity,tomic charges (Mulliken/APT), dipole moment, non linear opticalarameters (static electronic polarizability, anisotropy, first ordernd second order hyper polarizabilities) and other thermo dynami-al parameters were calculated using the Gaussian 03 package [36].y combining the results of the GAUSSVIEW [37] program withymmetry considerations, vibrational frequency assignments wereade with a high degree of accuracy and the vibrations match quiteell with the motions observed using the GAUSSVIEW program.
The calculated harmonic force constants and wavenumbers aresually higher than the corresponding experimental quantitiesecause of the combination of electron correlation effects and basiset deficiencies. The observed slight disagreement between theorynd experiment could be a consequence of the anharmonicity andhe general tendency of the quantum mechanical methods to over-stimate the force constants at the exact equilibrium geometry.herefore, in order to improve the calculated values in agreementith the experimental ones, it is necessary to scale down the calcu-
ated harmonic frequencies. The theoretical harmonic frequenciesreater than 1700 cm−1 are scaled by 0.958 in the and the scalingactor of 0.9614 is used for the frequencies less than 1700 cm−1
t B3LYP/6-311++G(d,p) level as predicted in the earlier refer-nces [38,39] while for B3LYP/6-311G(d,p) the scaling factor used
s 0.9668 as in Ref. [40]. Moreover, the better fit of observed andcaled frequencies are verified with statistical tools such as meaneviation, mean absolute deviation, RMS values and correlationo-efficient.
Fig. 1. Molecular structure with numbering of atoms of 1-(chloromethyl)-2-methylnaphthalene.
3.1. Prediction of Raman intensities
The Raman activities (SRa) calculated with the Gaussian 03 pro-gram were converted to relative Raman intensities (IRa) using thefollowing relationship derived from the intensity theory of Ramanscattering [41,42].
IRa = f (v0 − vi)4Si
vi[1 − exp(−(hcvi/kT))]
where �o is the laser exciting wavenumber in cm−1 (in this work,we have used the excitation wavenumber �o = 9398.5 cm−1, whichcorresponds to the wavelength of 1064 nm of a Nd:YAG laser), �i thevibrational wavenumber of the ith normal mode (in cm−1) and Si isthe Raman scattering activity of the normal mode �i, f (is a constantequal to 10−12) is a suitably chosen common normalization factorfor all peak intensities. h, k, c and T are Planck constant, Boltzmannconstant, speed of light and temperature in Kelvin, respectively.
4. Results and discussion
4.1. Molecular geometry
The molecular structure along with numbering of atoms of 1-ClM-2MN is obtained from Gaussian 03 and GAUSSVIEW programsand is as shown in Fig. 1. The global minimum energy obtainedby DFT/B3LYP structure optimization using 6-311G(d,p) and 6-311++G(d,p) basis sets for the title molecule are -924.25695714 a.u.and −924.26197735 a.u., respectively. The most optimized struc-tural parameters (bond length, bond angle and dihedral angle)calculated by DFT/B3LYP with 6-311G(d,p) and 6-311++G(d,p) basissets are compared with X-ray and electron diffraction experimen-tal data and represented in Table 1 in accordance with the atomnumbering scheme given in Fig. 1.
The C–C bonds in naphthalene are not of the same length inaccordance with the valence bond model of bonding in naphtha-lene which involves three resonance structures. So, in line withthe above said theory, the bonds C1–C2, C3–C4, C7–C8 and C9–C10are about 1.36 A, whereas the other C–C bonds are about 1.42 A.Generally, the theoretically calculated optimized bond lengths are
somewhat larger than the experimental values, because the theo-retical calculations refer to isolated molecules in the gaseous phasewhile it is in solid state for experimental results. From Table 1,the C–C bond lengths in the naphthalene ring were obtained in
P.B. Nagabalasubramanian et al. / Spectrochimica Acta Part A 85 (2012) 43– 52 45
Table 1Selected optimized geometrical parameters (bond length (Å) and bond angle (◦)) of 1-chloromethyl-2-methylnaphthalene.
6-311++G(d,p) basis sets are reported in Table 2. All vibrations areactive both in IR and Raman. The experimental FT-IR and FT-Ramanspectrum were shown in Figs. 2 and 3, respectively. The TED for eachnormal mode among the symmetry coordinates of the molecule
or numbering of atoms refer Fig. 1.RD data (a, b and c) from Refs. [40–42].lectron diffraction data (d) from Ref. [43].
he range of 1.371–1.431 A with B3LYP/6-311++G(d,p), which areuite close to the earlier literature values [43–46]. The C–C and C–Hond lengths calculated with B3LYP/6-311++G(d,p) for the groundtate of the title molecule agree within 0.01 A with the experimen-al findings. In spite of the fact that the influence of the basis set onhe C–C bond length is fairly small, it is obvious that the B3LYP/6-11G(d,p) basis over estimates the bond lengths alternation in theitle compound. The presence of methyl group in the naphthaleneing elongates the C–C bond length up to 1.5124 A and the C–Clond length in CH2–Cl is 1.849 A as represented in Table 1.
The equilibrium structure for the ground state shows that theaphthalene ring is planar, and also the C atoms of methylenend methyl groups are lying approximately in the plane as evidentrom the torsional angles C3–C2–C1–C21 (or C5–C6–C1–C21) and6–C1–C2–C17 (or C4–C3–C3–C17) in the range ca. 177–179◦.
.2. Vibrational assignments
The maximum number of potentially active observable fun-amentals of a non-linear molecule, which contains N atoms, is
qual to (3N − 6) apart from three translational and three rotationalegrees of freedom [47,48]. Hence, 1-ClM-2MN molecule has 24toms with 66 normal modes of vibrations and considered under1 point group symmetry.
The detailed analysis of fundamental modes of vibration withFT-IR and FT-Raman experimental frequencies, unscaled and scaledvibrational frequencies, IR and Raman intensities, Raman activities,and TED of 1-ClM-2MN using B3LYP method with 6-311G(d,p) and
Fig. 2. Experimental FT-infrared spectrum of 1-(chloromethyl)-2-methylnaphthalene.
a Wavenumbers scaled by the scaling factor of 0.9668.b Wavenumbers > 1700 cm−1 were scaled by 0.958 and the scaling factor of 0.9614 for wavenumbers < 1700 cm−1.
P.B. Nagabalasubramanian et al. / Spectroc
Fm
wpic
cdcialisb
C(sr
4
3vsismsas3iaaTfl
TMm
ig. 3. Experimental FT-Raman spectrum of 1-(chloromethyl)-2-ethylnaphthalene.
as calculated. A complete assignment of the fundamentals wasroposed based on the calculated TED values, infrared and Raman
ntensities. After applying uniform scaling factors, the theoreticalalculation reproduces the experimental data well.
In order to investigate the performance and vibrational frequen-ies for the title compound, the mean deviation, mean absoluteeviation, root mean square deviation or standard deviation andorrelation co-efficient between the unscaled calculated and exper-mental frequencies were calculated for B3LYP with 6-311G(d,p)nd 6-311++G(d,p) basis sets. These parameters are again calcu-ated between the scaled and experimental frequencies and givenn Table 3. These results indicates that B3LPY/6-311++G(d,p) basiset calculations approximate the experimental frequencies muchetter than 6-311G(d,p) basis set results.
For 1-ClM-2MN, the vibrational modes are C–H vibrations,–C and Ring vibrations, CH3 (methyl group) vibrations, CH2methylene group) vibrations, C–Cl vibrations. These vibrations aretretching, bending (in and out-of bending), scissoring, wagging,ocking, twisting and torsion modes.
.2.1. C–H vibrationsNormally, C–H stretching vibrations occur in the region
200–3000 cm−1 in the heteroatomic structure and moreover theseibrations are independent of the nature and position of the sub-tituent [49,50]. Most of the aromatic compounds have nearly fournfrared peaks in the region 3080–3010 cm−1 due to ring C–Htretching bonds [51,52]. This title molecule has six adjacent C–Hoieties with two fused benzene rings and the expected six C–H
tretching vibrations are C3–H11, C4–H12, C7–H13, C8–H14, C9–H15nd C10–H1. Accordingly, in this title compound, the medium inten-ity peak at 3050 cm−1 in FT-IR and the peaks at 3070 (strong),020 cm−1 (weak) in FT-Raman are assigned to symmetric stretch-
ng vibrations while the asymmetric stretching vibrations aressigned to the weak peaks at 2990 and 2980 cm−1 of FT-IR and
t 2995 cm−1 of FT-Raman as shown in Figs. 2 and 3, respectively.he substituent in the naphthalene ring produces the decrease ofrequency of some CH stretching modes as expected from the ear-ier predicted values. In general, most of the stretching modes are
able 3ean deviation, mean absolute deviation, RMS and correlation coefficient between the
ethylnaphthalene.
Parameters 6-311G(d,p)
Unscaled andexperimental
Scaleexpe
Mean deviation (cm−1) 50.9 8.1
Mean absolute deviation (cm−1) 39.5 19.4
RMS (or) S.D. (cm−1) 74.8 27.8
Correlation co-efficient (r) 0.9998 0.99
himica Acta Part A 85 (2012) 43– 52 47
pure stretching modes as is evident from TED column in Table 2;they almost contribute around 100%.
The C–H in plane bending vibrations usually occurs in the region1430–990 cm−1 and is very useful for characterization purposes[53]. The bands due to C–H in-plane ring vibration interactingsomewhat with C–C stretching vibration are observed as a numberof m–w intensity sharp bands in the region 1000–1300 cm−1. In thisstudy, the weak FT-IR peaks at 1160 and 1130 cm−1 and the strong-medium FT-Raman peaks at 1420, 1210, 1170 and 1140 cm−1 areassigned to C–H in-plane-bending vibrations as reported in Table 2.
The aromativity of the compound was obviously proved by thepresence of strong peak below 900 cm−1 and the substitution pat-terns on the ring can be judged from the out of plane bending of thering C–H bond in the region 900–675 cm−1 which are more infor-mative [54]. Besides, the C–H out-of-plane bending vibrations arestrongly coupled vibrations and occur in the region 900–667 cm−1
[55]. In the present study, the peaks at 980(w), 950(m), 795(s),750(s) and 730 cm−1 (s) in FT-IR and the weak and strong bandsof FT-Raman at 970 and 860 cm−1 confirm the C–H out of planebending vibrations which agrees well with the above said litera-ture values. The TED in Table 2 also shows the mixed contributionof approximately 80% and 25% for these vibrations (mode nos.37–38, 40, 42 and 44–46). In general the aromatic C–H vibrations(stretching, in-plane and out-of-plane bending) calculated theoret-ically are in good agreement with experimentally accepted values[56,57]. The change in the frequencies of these deformations fromthe values in naphthalene is almost determined exclusively by therelative position of the substituent and is almost independent oftheir nature.
4.2.2. C–C and ring vibrationsThe ring stretching vibrations are very much important in the
spectrum of naphthalene derivatives and are highly characteris-tic of the aromatic ring itself. Naphthalene ring C C stretchingvibrations are expected in the region 1620–1390 cm−1 and thesevibrations are found to make a major contribution in the IR andRaman spectra [58]. In view of that, the C C aromatic stretchis observed in 1600(m), 1550(w) and 1510(s) cm−1 in the FT-IRspectrum and the strong peak at 1575 cm−1 in the FT-Raman spec-trum. These vibrations are in agreement with the scaled theoreticalassignments given by DFT. The strong peaks at 870 and 700 cm−1
in FT-IR, 1370 and 1170 cm−1 in FT-Raman are assigned to C–Cstretching vibrations which are coupled vibrations with CH in-plane-bending, C–C–C (stretching and bending) and ring vibrations,respectively as marked in the TED column of Table 2.
The ring deformation and breathing vibrations in FT-IR areassigned to 1340, 1320 and 1190 cm−1, respectively while the ringwagging vibrations are assigned at 530, 230 and 170 cm−1. Most ofthese vibrations are mixed up with C–H, C–C–C and C–Cl vibrationsas shown in the TED column in Table 2.
4.2.3. Methyl group vibrationsThe C–H stretching in methyl groups occurs at lower frequen-
cies than those of aromatic ring (3100–3000 cm−1). Whenever a
unscaled/scaled and experimental vibrational frequencies for 1-(chloromethyl)-2-
6-311++G(d,p)
d andrimental
Unscaled andexperimental
Scaled andexperimental
48.7 2.937.2 16.471.3 18.5
98 0.9998 0.9998
4 ectrochimica Acta Part A 85 (2012) 43– 52
mmasifR[iiaiwaap[
4
vtovwdwcaawCo
4
bCg[risda(batiaptvc
4
mvatCe(
Table 4Mulliken atomic charges of 1-(chloromethyl)-2-methylnaphthalene performed atB3LYP methods with 6-311G(d,p) and 6-311++G(d,p) basis sets.
molecule, �˛ is the dipole moment, ˛˛ˇ is the mean polarizability,ˇ˛ˇ� is the first and �˛ˇ�ı is the second dipole hyperpolarizabil-ity. The number of independent components for these tensors is
Table 5Theoretically computed mean polarizability (˛˛ˇ in au), anisotropy (˛), first (ˇ˛ˇ�
in 10−30 esu), second (�˛ˇ�ı in Debye – Å3) hyperpolarizability, dipole moment(Debye) and q(CH3) of 1-(chloromethyl)-2-methylnapthalene.
Parameters B3LYP/6-311G(d,p)B3LYP/6-311++G(d,p)
Mean polarizability (˛˛ˇ) 144.729 158.057Anisotropy (˛) 105.74 98.41
8 P.B. Nagabalasubramanian et al. / Sp
ethyl group is present in a compound, it gives rise to two asym-etric and one symmetric stretching vibration [6]. Moreover, the
symmetric stretch is usually at higher wavenumber than theymmetric stretch. In this present work, the CH3 symmetric stretch-ng frequency is assigned at 2870 cm−1, whereas CH3 asymmetricrequencies are assigned at 2910 cm−1 (FT-IR) and 2920 cm−1 (FT-aman), respectively, which are in agreement with the literature6,57]. The medium intensity peak at 1450 cm−1 and the strongntensity peak at 1430 cm−1 of FT-IR are assigned to CH3 scissor-ng vibrations whereas the peaks at 1030 and 1005 cm−1 (FT-IR)nd the weak peak at 1010 cm−1 (FT-Raman) are assigned to CH3n-plane rocking modes which are appeared as coupled vibrations
ith C–C stretching modes (mode nos. 34–36). The CH3 waggingnd twisting vibrations are assigned at 1380 and 130 cm−1 in FT-IRs shown at TED in Table 2. The methyl group assignments pro-osed in this study is also in agreement with the literature values59,60].
.2.4. Methylene vibrationsIn this molecule, the asymmetric and symmetric stretching
ibrations are observed at 3010 and 2950 cm−1 in FT-IR, respec-ively. Generally, the scissoring band in the spectra of hydrocarbonsccurs nearly at 1465 cm−1 while methylene twisting and waggingibrations are observed in the region 1350–1150 cm−1 which areeaker than those resulting from methylene scissoring. In accor-ance with the above reference, the peak occurred at 1480 cm−1
ith TED of 58% is assigned to CH2 scissoring and moreover it theoupled vibrations with CH3 while the CH2 wagging vibrations aressigned to 1270 and 1250 cm−1 in FT-IR as in Fig. 2. The peakst 960 and 820 cm−1 in FT-IR are assigned to CH2 rocking modeshich are coupled with C–C and CH3 vibrations. All the vibrations ofH2 computed by B3LYP method agree well with the experimentalbservations.
.2.5. C–Cl vibrationsThe presence of halogen on alkyl substituted aromatic ring can
e detected indirectly from its electronic impact on the in-plane–H bending vibrations [61]. The C–Cl stretching vibrations giveenerally strong bands in the region 730–580 cm−1 [62]. Mooney63] assigned vibrations of C–X group (X = Cl, Br, I) in the frequencyange of 1129–480 cm−1. Accordingly, a very strong band observedn FT-IR spectrum at 630 cm−1 (mode no. 50) is assigned to C–Cltretching. The predicted values (633 and 634 cm−1) show a smalleviation ca. 3–4 cm−1 with FT-IR data and the TED value of 35%s reported in Table 2. There is an another strong peak at 695 cm−1
mode no. 48) which is also assigned as C–Cl stretching vibrationut it is the coupled vibration with CCCC has the TED value of 25%s shown in Table 2 and may be due to CH2–Cl stretching vibra-ion, imply that the compound is a monochlorinated compoundn the alkyl substituted aromatic ring. The peak at 300 cm−1 isssigned to CC–Cl in-plane-bending vibration whereas the out-of-lane CC–Cl bending vibrations are assigned to 80 cm−1 (FT-IR) andorsional CCC–Cl vibrations to 60 cm−1 (FT-Raman), both are mixedibrations as shown in Table 2. The remainder of the observed andalculated frequencies accounted in Table 2.
.3. Atomic charges and nonlinear optical properties
The atomic charges of 1-ClM-2MN are calculated using B3LYPethod with 6-311G(d,p) and 6-311++G(d,p) basis sets and the
alues are tabulated in Table 4. The more negative values on C17tom of CH3 group lead to a redistribution of electron density. On
he other hand, atomic charges of hydrogen (H18 and H20) in theH3 group are also almost identical but H19 has marginal differ-nce with higher basis set. The substitution of methyl group in the-position of naphthalene ring makes C2 atom more acidic which
H23 0.1851 0.2586Cl24 −0.1216 −0.3556
leads to more positive charge on it. Also, the study infers that themore positive charge on C1 atom makes it more acidic. The substi-tution of CH2Cl group in the aromatic ring leads to a redistributionof electron density and the �-electron withdrawing character ofthe chlorine atom in this title compound is demonstrated by thedecrease of electron density on C21 atom as in Table 4. But, theatomic charges in the CH2 group are almost identical.
Atomic charges of the investigated 1-ClM-2MN are evaluatedaccording to the atomic polar tensor (APT) method. The sum of theAPT charges over the methyl group, q(CH3) and the dipole momentcomputed at B3LYP with 6-311G(d,p) and 6-311++G(d,p) are alsolisted in Table 5. As seen in the table, dipole moments are somewhatsmall, consistently with the high q(CH3) charges which is well agreewith the report of earlier literature [24].
The energy of an uncharged liner molecule in a weak, homoge-nous electric field can be written as
Ep = E0 − �˛F˛ −(
12
)˛˛ˇF˛Fˇ −
(16
)ˇ˛ˇ� F˛FˇF�
−(
124
)�˛ˇ�ıF˛FˇF� Fı + · · ·
where F is the field at the origin, E0 is the energy of the free
First order hyper polarizability (ˇ˛ˇ�) 0.1115 0.0798Second order hyper polarizability (�˛ˇ�ı)484.78 488.85q(CH3) 0.025741 0.038657Dipole moment 2.6407 2.5554
ectrochimica Acta Part A 85 (2012) 43– 52 49
rtp3r
(omti
˛
ˇ
w
ˇ
ˇ
ˇ
�
Lfi〈Mtdcnmpm1is
4
tcct
tdwcbt
Table 6Thermodynamic properties at different temperatures at the B3LYP/6-311++G(d,p)level for 1-(chloromethyl)-2-methylnapthalene.
egulated by symmetry. In the presence of an applied electric field,he energy of a system is a function of the electric field. First hyper-olarizability is a third rank tensor that can be described by a
× 3 × 3 matrix and the 27 components of the 3D matrix can beeduced to 10 components due to the Kleinman symmetry [64].
The nonlinear optical properties such as the dipole moment�˛), polarizability (˛˛ˇ), anisotropy (˛), first (ˇ˛ˇ� ) and sec-nd (�˛ˇ�ı) dipole hyperpolarizability are calculated by DFT/B3LYPethod using 6-311G(d,p) and 6-311++G(d,p) basis sets, based on
he finite filed approach using the following formulae and tabulatedn Table 5.
˛ˇ =(
˛xx + ˛yy + ˛zz
3
)
˛ =(
12
)1/2[(˛xx − ˛yy)2 + (˛yy − ˛zz)2 + (˛zz − ˛xx)2]
1/2
˛ˇ� =√
ˇ2x + ˇ2
y + ˇ2z
here
x = 35
[ˇxxx + ˇxyy + ˇxzz]
y = 35
[ˇyyy + ˇyxx + ˇyzz]
z = 35
[ˇzzz + ˇzxx + ˇzyy]
˛ˇ�ı =(
�xxxx + �yyyy + �zzzz + 2�xxyy + 2�yyzz + 2�zzxx
5
)
ibrando et al. [24] concluded that the smallest 〈˛〉 values wereound for isomers with both the CH3 functional groups in � position,ntermediate values were obtained for �, �-isomers and the largest˛〉 values were calculated for isomers methylated in � positions.
oreover, it is illustrious that the accurate polarizability compu-ations require usage of flexible basis sets including polarized andiffused functions [65] as well as of the introduction of electronorrelation methods [66–68]. The electronic polarizability (〈˛〉) ofaphthalene molecule calculated from Laser stark spectroscopyeasurements in gas phase [69] was 117.4 a.u. Accordingly, in the
resent study, the electronic polarizability calculated by B3LYPethods with 6-311G(d,p) and 6-311++G(d,p) are 144.73 a.u. and
58.06 a.u., respectively implies that the electronic polarizabilitys remarkably influenced by the presence and position of methylubstituent.
.4. Thermodynamic properties
On the basis of vibrational analysis at B3LYP/6-311G(d,p) level,he standard statistical thermodynamic functions: standard heatapacities (C0
p,m) standard entropies (S0m), and standard enthalpy
hanges (H0m) for the title compound were obtained from the
heoretical harmonic frequencies and listed in Table 6.From Table 6, it can be observed that these thermodynamic func-
ions are increasing with temperature ranging from 100 to 700 Kue to the fact that the molecular vibrational intensities increase
ith temperature [70]. The correlation equations between heat
apacity, entropy, enthalpy changes and temperatures were fittedy quadratic formulas and the corresponding fitting factors (R2) forhese thermodynamic properties are 0.9987, 1.0000 and 0.9999,
Fig. 4. Correlation graph of heat capacity and temperature for 1-(chloromethyl)-2-methylnaphthalene.
respectively. The corresponding fitting equations are as follows andthe correlation graphics of those show in Figs. 4–6.
Fig. 5. Correlation graph of entropy and temperature for 1-(chloromethyl)-2-methylnaphthalene.
50 P.B. Nagabalasubramanian et al. / Spectrochimica Acta Part A 85 (2012) 43– 52
Fm
Afpoctw
4
ootmlg
iwHttmecpe−air
TCs
Fig. 7. The atomic orbital compositions of the frontier molecular orbital for 1-(chloromethyl)-2-methylnaphthalene.
ig. 6. Correlation graph of enthalpy and temperature for 1-(chloromethyl)-2-ethylnaphthalene.
ll the thermodynamic data supply helpful information for theurther study on the 1-ClM-2MN. They can be used to com-ute the other thermodynamic energies according to relationshipsf thermodynamic functions and estimate directions of chemi-al reactions according to the second law of thermodynamics inhermochemical field [70]. Notice: all thermodynamic calculationsere done in gas phase and they could not be used in solution.
.5. HOMO–LUMO analysis
The total energy, energy gap and dipole moment have influencen the stability of a molecule. We have performed optimization inrder to investigate the energetic behavior and dipole moment ofitle compound in solvent and gas phase. The total energy, dipole
oment and frontier molecular orbital energies have been calcu-ated with B3LYP/6-311G(d,p) level. Results obtained in solvent andas phase are listed in Table 7.
HOMO and LUMO are very important parameters for chem-cal reaction. We can determine the way the molecule interacts
ith other species; hence, they are called the frontier orbitals. TheOMO is the orbital that primarily acts as an electron donor and
he LUMO is the orbital that largely acts as the electron accep-or, and the gap between HOMO and LUMO characterizes the
olecular chemical stability. The energy gap between the high-st occupied and the lowest unoccupied molecular orbitals, is aritical parameter in determining molecular electrical transportroperties because it is a measure of electron conductivity. Thenergy values of HOMO are computed −6.26819, −6.23445 and6.20969 eV and LUMO are −1.79923, −1.76848 and −1.74617 eV,
nd the energy gap values are 4.46896, 4.46597 and 4.46352 eVn DMSO, chloroform and gas phase for 1-ClM-2MN molecule,espectively. Surfaces for the frontier orbitals were drawn to
able 7alculated energies values of 1-(chloromethyl)-2-methylnaphthalene in gas andolvent (DMSO and chloroform) phase.
understand the bonding scheme of present compound. Weexamine the molecular orbitals (MO) for title molecule: thehighest occupied MO and the lowest unoccupied MO whichwe denote HOMO and LUMO, respectively. These MOs for gasphase are outlined in Fig. 7. The positive phase is red andthe negative one is green. According to Fig. 7, the HOMOof 1-ClM-2MN presents a charge density localized over thenaphthalene ring, Cl atom and CH2 group of CH3 group,however, LUMO is characterized by a charge distribution onall molecule expect of hydrogen atoms in CH3 group. TheHOMO → LUMO transition implies an electron density transfer.Moreover lower in the HOMO and LUMO energy gap explainsthe eventual charge transfer interactions taking place within themolecule.
Dipole moment reflects the molecular charge distribution andis given as a vector in three dimensions. Therefore, it can be usedas descriptor to depict the charge movement across the molecule.Direction of the dipole moment vector in a molecule depends onthe centres of positive and negative charges. Dipole moments arestrictly determined for neutral molecules. We can say that in going
from the gas phase to the solvent phase, the dipole moment valueincreases (Table 7).
P.B. Nagabalasubramanian et al. / Spectrochimica Acta Part A 85 (2012) 43– 52 51
Table 8Theoretical electronic absorption spectra of 1-chlorometyl-2-methylnapthalene (absorption wavelength, � (nm), excitation energies, E (eV) and oscillator strengths (f)) usingTD–DFT/B3LYP/6-311++G(d,p) method in gas and solvent (DMSO and chloroform) phase.
DMSO Chloroform Gas Gas Assignment
� (nm) E (eV) f � (nm) E (eV) f � (nm) E (eV) f Major contributiona
307.64 4.0302 0.1461 307.97 4.0258 0.1482 304.79 4.0679 0.1032 H → L (95%) �–�*288.33 4.3001 0.0186 288.63 4.2957 0.0191 288.56 4.2966 0.0109 H − 1 → L (59%), H → L + 1 (40%) �–�*
6.30
4
gtafaeTtomoff2cbccwolb
5
d61fcrlRcetrvodUttspsa
R
[[[[[
[[[[[[[
[[[[
[[
[
[
[[[[[[[[
[
[
[[
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[[[[[
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[
246.77 5.0243 0.0127 246.88 5.0219 0.0109 24
a H: HOMO, L: LUMO.
.6. UV–vis spectra analysis
Ultraviolet spectra analyses of 1-ClM-2MN have been investi-ated by theoretical calculation. In order to understand electronicransitions of compound, TD–DFT calculations on electronicbsorption spectra in gas phase and solvent (DMSO and Chloro-orm) were performed. The calculated frontier orbital energies,bsorption wavelengths (�), oscillator strengths (f) and excitationnergies (E) for gas phase and solvent are illustrated in Table 8.he major contributions of the transitions were designated withhe aid of Swizard program [71]. Calculations of the molecularrbital geometry show that the visible absorption maxima of thisolecule correspond to the electron transition between frontier
rbitals such as translation from HOMO to LUMO. As can be seenrom Table 8, the calculated absorption maxima values have beenound to be 304.79, 288.56, 246.30 nm for gas phase, 307.64, 288.33,46.77 nm for DMSO solution and 307.97, 288.63, 246.88 nm forhloroform solution at DFT/B3LYP/6-311++G(d,p) method. As cane seen, all calculations performed are very close. In view of cal-ulated absorption spectra, the maximum absorption wavelengthorresponds to the electronic transition from HOMO to LUMOith 95% contribution. This transition is predicted as �–�*. The
ther wavelength, excitation energies, oscillator strength, calcu-ated counterparts with major contributions and assignments cane seen in Table 8.
. Conclusion
The FT-IR and FT-Raman spectrum were recorded and theetailed vibrational assignments using HF and DFT methods with-311G(d,p) and 6-311++G(d,p) basis sets were presented for-(chloromethyl)-2-methylnaphthalene, for the first time. The dif-erence between the corresponding wavenumbers (observed andalculated) is very small for most of fundamentals. Therefore, theesults presented in this work for 1-ClM-2-MN indicate that thisevel of theory is reliable for the prediction of both infrared andaman spectra of the title compound. Furthermore, theoreticalalculations give the thermodynamic properties (heat capacity,ntropy and enthalpy) for the compound. It can be observed thathese thermodynamic functions are increasing with temperatureanging from 100 to 700 K due to the fact that the molecularibrational intensities increase with temperature. We have doneptimization in order to investigate the energetic behavior andipole moment of title compound in the gas phase and solvent.V–vis spectral analyses of 1-ClM-2-MN have been analyzed by
heoretical calculation. In order to understand electronic transi-ions of compound, TD–DFT calculations on electronic absorptionpectra in gas phase and solvent (DMSO and chloroform) wereerformed. The electronic spectrum corresponds to the �–�* tran-ition. We hope the results of this study will help researchers tonalysis and synthesis of new materials.
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