Quantum mechanical study of the structure and vibrational spectroscopic (FT-IR and FT-Raman), first-order hyperpolarizability, NBO and HOMO−LUMO studies of 4-bromo-3-nitroanisole

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

Contents lists available at SciVerse ScienceDirect

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Quantum mechanical study of the structure and vibrational spectroscopic (FT-IR and FT-Raman), first-order hyperpolarizability, NBO and HOMOLUMO studies of 4-bromo-3-nitroanisole V. Balachandran a,⇑, V. Karunakaran b a b

PG and Research Department of Physics, A A Government Arts College, Musiri, Tiruchirappalli 621 211, India PG and Research Department of Physics, Government Arts College, Ariyalur 621 713, India

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

" The FT-IR and FT-Raman spectra of

4-bromo-3-nitroanisole were analyzed. " The calculations were carried out for 4-bromo-3-nitroanisole at HF and B3LYP methods. " Thermodynamic properties were determined at various temperatures.

a r t i c l e

i n f o

Article history: Received 13 September 2012 Received in revised form 17 December 2012 Accepted 21 December 2012 Available online 23 January 2013 Keywords: 4-Bromo-3-nitroanisole Vibrational spectra DFT calculations Vibrational assignments Thermodynamic functions

a b s t r a c t The FT-IR and FT-Raman spectra of 4-bromo-3-nitroanisole (BNA) molecule have been recorded in the region 4000400 cm1 and 3500100 cm1, respectively. Optimized geometrical structure, harmonic vibrational frequencies, intensities, reduced mass, force constants and depolarization ratio have been computed by ab initio HF and the B3LYP density functional levels using 6-311++G (d,p) basis set. The observed FT-IR and FT-Raman vibrational frequencies are analyzed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The first-order hyperpolarizability (b) of the investigated molecule were computed using DFT calculations. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) were calculated and analyzed. The influences of bromine atom, nitrile group and methyl group on the geometry of benzene and its normal modes of vibrations have also been discussed. Ó 2013 Elsevier B.V. All rights reserved.

Introduction Anisole, C6H5OCH3 (methyl phenyl ether), is a clear liquid that is soluble in ether and alcohol and insoluble in water; boiling point 155 °C. Anisole is more electron rich than benzene because of the resonance effect of the methoxy group upon the aromatic ring [1]. Anisole reacts with electrophiles in the electrophilic aromatic

⇑ Corresponding author. Tel.: +91 0431 2591338; fax: +91 4326 262630. E-mail address: [email protected] (V. Balachandran). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.12.070

substitution reaction more quickly than benzene. For anisole the two effects, i.e. back-donation and conjugation, can be competitive and their relative weight in determining the electronic properties of the molecule can be conformation dependent [2]. Anisole is used in perfumery, chemical syntheses and an insect pheromone [3]. Particularly p-nitroanisole is a bio-agent and it is mainly used to synthesize amino anisole, dyes and medicine. The application of nitroanisole as a detector for middle infrared interferometry [4] has been confirmed. Since the nitroanisole absorbs IR radiation as heat it is possible to estimate the IR intensity distribution on the nitroanisole from the diffraction pattern made by visible larger

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

light that is transmitted through it. It is used to measure the mono phenolase activity of polyphenol oxidize from fruits and vegetables [5]. Nitroanisole is a simple device which is used to detect mid-IR radiation. The nitroanisole exhibits a thermal lens effect [6–8], in which the refractive index is dependent upon temperature. This effect results in phase modulation on visible light, in direct response to intensity of the incident IR radiation, which is absorbed as heat. In the case of IR laser interferometry, interference fringe patterns that are created by the IR laser on the nitroanisole is observed as the refractive index distribution; hence the nitroanisole functions as a phase grating for visible light. It is, therefore, conceivable to estimate the IR intensity distribution on the nitroanisole by analyzing the diffraction pattern made by a visible laser, which is transmitted through the nitroanisole. Also, since a two dimensional device using the nitroanisole does not require matrix structure, it is expected that the measurement system must have high spatial resolution, equivalent to that of existing IR cameras. Owing to these applications and the reliable properties of anisole, a complete vibrational study on BNA has been undertaken. More recently, the experimental vibrational spectra of p-nitroanisole, 2-nitroanisole, thioanisole and 3-bromoanisole [9–12] have been investigated in comparison with HF and B3LYP values. Literature survey reveals that, to the best of our knowledge no HF and B3LYP level calculations of BNA have been reported so far. In the present work, the FT-IR and FT-Raman spectra of BNA have been studied. The HF and B3LYP level with 6-311++G (d,p) basis set have been performed to obtain the ground state optimized geometries and the vibrational wave numbers of the different normal modes as well as to predict the corresponding intensities for the different modes of the molecule. Experimental details 4-bromo-3-nitroanisole (BNA) was provided by M/s Aldrich Chemicals, USA, which is of spectroscopic grade and hence used for recording the spectra as such without any further purification. The room temperature Fourier Transform infrared spectrum of BNA was measured in the 4000–400 cm1 region at a resolution of ±1 cm1 using a BRUKER IFS-66V FT-IR spectrometer equipped with a cooled MCT detector for the mid-IR range. KBr pellets were used in the spectral measurements. The FT-Raman spectra of BNA were recorded on a BRUKER IFS-66V model interferometer equipped with an FRA-106 FT-Raman accessory in the 3500– 100 cm1 Stokes region using the 1064 nm line of a Nd:YAG laser for excitation operating at 200 mW power. The reported wave numbers are expected to be accurate within ±1 cm1. Computational methods The molecular structure of BNA and corresponding vibrational harmonic frequencies were calculated using HF and Becke3–Lee– Yang–Parr (B3LYP) combined with 6-311++G (d,p) basis set using GAUSSIAN 09 program package [13] without any constraint on the geometry. The harmonic vibrational frequencies have been analytically calculated by taking the second-order derivative of energy using the same level of theory. Transformation of force field from Cartesian to symmetry coordinate, scaling, subsequent normal coordinate analysis, and calculations of TED, IR and Raman intensities were made on a PC with the version V7.0-G77 of the MOLVIB program written by Sundius [14,15]. To achieve a close agreement between observed and calculated frequencies, the least-square fit refinement algorithm was used. By combining the results of the GAUSSVIEW [16] program with symmetry considerations, along with the available related molecules, vibrational frequency assignments were made with a high degree of accuracy.

285

Prediction of Raman intensities The Raman intensities (Ii) were calculated from the Raman activities (Si) obtained with the Gaussian 09 program, using the following relationship derived from the intensity theory of Raman scattering [17–19].

Ii ¼

f ðt0  ti Þ4 S i ti ½1  expðhcti Þ=kT

ð1Þ

where t0 is the exciting frequency (in cm1units), ti is the vibrational wavenumber if the ith normal mode, h, c and k are the universal constants and f is the suitably chosen common scaling factor for all the peak intensities. The simulated IR and Raman spectra have been plotted using Lorentzian band shapes with FWHM bandwidth of 10 cm1. Results and discussion Rotational conformers and molecular geometry To obtain stable conformer geometry, the self consistent field (SCF) energy calculation is performed on BNA as shown in Fig. 1. The DFT structure optimizations of BNA have shown that conformer ‘‘b’’ (O-trans) (Table 1). The maximum number of potentially active observable fundamentals of a non-linear molecule which contains N atoms is equal to (3N6), apart from three translational and three rotational degrees of freedom [20]. Since the molecule do not possess any rotational, reflection or inversion symmetry, the molecule is considered under Cs point group symmetry. The comparative optimized structural parameters such as bond lengths, bond angles and dihedral angles are presented in Table 2. From the theoretical values, it is found that most of the optimized bond lengths are slightly larger than the experimental values due to the fact that the theoretical calculations belong to isolated molecules in gaseous phase and the experimental results belong to molecules in solid state [21]. Comparing bond angles and lengths of B3LYP with those of HF, as a whole the formers are bigger than later and the B3LYP calculated values correlates well compared with the experimental data. Although the differences, calculated geometrical parameters represent a good approximation and they are the bases for the calculating other parameters, such as vibrational frequencies and thermodynamics properties. The comparative graphs of bond lengths and bond angles of BNA for two sets are presented in Figs. S1 and S2, respectively. Since the experimental X-ray diffraction data of BNA molecule is unavailable, the experimental data of similar kind of molecule is presented in Table 2 for comparative purpose [12]. When comparing experimental values, the computed bond lengths and bond angles at B3LYP/6311++G (d,p) method are slightly larger, because the theoretical calculations are performed upon isolated molecule in the gaseous state and the experimental results are performed on the solid phase of the molecule [12]. The phenyl ring appears little distorted and angles slightly out of perfect hexagonal structure. It is due to the substitutions of the heavy atom bromine atom, NO2 and OACH3 groups in the place of H atoms. The order of the optimized bond lengths of the six CAC bonds of the ring as C5AC6 < C4AC5@C3AC4@C2AC3@C1AC2 < C1AC6. The breakdown of hexagonal symmetry of the benzene ring is obvious from the elongation of C1AC2 (1.39 Å) and C1AC6 (1.40 Å) from the remaining C2AC3 (1.37 Å) bond lengths since the replacement of bromine atom and methyl group with different masses. The CABr bond distance of cal. 1.90 Å by B3LYP/6-311++G (d, p) is just 0.033 Å lower than the reported experimental value of 1.867 Å for 4-methylphenylamine [22,23].

286

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

Fig. 1. Molecular structure with numbering of atoms of 4-bromo-3-nitroanisole: (a) O-cis and (b) O-trans.

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

287

Table 1 Calculated energies and energy difference O-cis and O-trans of 4-bromo-3-nitroanisole with HF and DFT/B3LYP using 6-311++G (d,p) methods. Conformers

O-cis O-trans a

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

B3LYP/6-311++G (d,p) 1

Energy (hartree)

Energy (kJ mol

3119.625563 3119.632153

8190577.540789 8190594.843728

)

a

Energy differences (kJ mol 17.302939 0.000000

1

)

Energy (hartree)

Energy (kJ mol1)

Energy differencesa (kJ mol1)

3124.684981 3124.688503

8203861.044101 8203870.291979

9.247878 0.000000

Energies of the O-cis conformer relative to the most stable O-trans conformer.

The C1AO7 bond distance of cal. 1.35 Å is just 0.02 Å lower than the reported experimental value of 1.370 Å [24]. According to the calculated values (B3LYP/6-311++G (d, p)), the order of the optimized bond angle are as C6AC1AC7 < C3AC4 C5 < C2AC1AC6 < C1AC2AC3 < C1AC6AC5 < C4AC5AC6 < C2AC3AC4 < C2AC1AC7. The asymmetry of the benzene ring is also evident from the negative deviation of C2AC1AC6, C1AC2AC3 and C4AC5AC6 and the positive deviation of C2AC3AC4 and C1AC6AC5 from the experimental values. The bond angle of C2AC1AC6 2.2 Å compressed than the bond angle C4AC5AC6, since the substitution of OACH3 at C1. The bond angle of C5AC4ABr16 cal. 117.73(°) is just 3.33 Å greater than the reported value of 114.4 Å [25,26]. Normal coordinate analysis was carried out to provide a complete assignment of the fundamental vibrational frequencies for the molecule. For this purpose, the full sets of standard internal coordinates (containing-redundancies) are defined as given in Table 3. From these a non-redundant set of local symmetry coordinates was constructed by suitable linear combination of internal coordinates and they are presented in Table 4. The theoretically calculated force field was transformed to this later set of vibrational coordinates and was used in all subsequent calculations. For a visual comparison, the observed and simulated FTIR and FT-Raman spectra are shown in Figs. 2 and 3, respectively.

Vibrational assignments The BNA consist of 18 atoms, hence undergoes 48 normal modes of vibrations. Of the 48 normal modes of vibrations, 33 modes of vibrations are in-plane and remaining 15 are out-ofplane. The bands that are in the plane of the molecule is represented as A0 and out-of-plane as A00 . Thus the 48 normal modes of vibrations of BNA are distributed as I’Vib = 33 A0 + 15 A00 . In agreement with CS symmetry all the 48 fundamental vibrations are active in both Raman scattering and IR absorption. The harmonic-vibrational frequencies calculated for BNA at HF and B3LYP levels using the triple split valence basis set along with the diffuse and polarization function 6-311++G (d,p), observed FT-IR and FT-Raman frequencies for various modes of vibrations and descriptions concerning the assignment have been presented in Table 5. Comparison of frequencies calculated at HF with the experimental values reveals the over estimation of the calculated vibrational modes due to the neglect of anharmonicity in real system. Inclusion of electron correlation in the density functional theory to certain extend makes the frequency values smaller in the comparison with the HF frequency data. Reduction in the computed harmonic vibrations, although basis set sensitive are only marginal as observed in the B3LYP values using 6-311++G (d,p). Any way

Table 2 Optimized geometrical parameters of 4-bromo-3-nitroanisole by HF/6-311++G (d,p) and B3LYP/6-311++G (d,p) methods. Bond length

C1AC2 C1AC6 C1AO7 C2AC3 C2AH12 C3AC4 C3AN13 C4AC5 C4ABr16 C5AC6 C5AH17 C6AH18 O7AH8 C8AH9 C8AH10 C8AH11 N13AO14 N13AO15

a

Value (Å)

Bond angle

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

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

Exp.a

1.380 1.395 1.337 1.388 1.070 1.375 1.469 1.394 1.889 1.372 1.073 1.074 1.405 1.085 1.079 1.085 1.182 1.188

1.390 1.402 1.356 1.400 1.079 1.400 1.489 1.402 1.905 1.382 1.082 1.083 1.427 1.095 1.088 1.095 1.220 1.227

1.362 1.384 1.370 1.427 1.08 1.385 1.363 1.867 1.440 1.08 1.08 1.09 1.09 1.09

Geometric parameters determined with X-ray diffraction method from Ref. [12].

C2AC1AC6 C2AC1AC7 C6AC1AC7 C1AC2AC3 C1AC2AH12 C3AC2AH12 C2AC3AC4 C2AC3AN13 C4AC3AN13 C3AC4AC5 C3AC4ABr16 C5AC4ABr16 C4AC5AC6 C4AC5AH17 C6AC5AH17 C1AC6AC5 C1AC6AH18 C5AC6AH18 C1AO7AC8 O7AC8AH9 O7AC8AH10 O7AC8AH11 H9AC8AH10 H9AC8AH11 H10AC8AH11 C3AN13AO14 C3AN13AO15 O14AN13AO15

Value (°) HF/6-311++G (d,p)

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

Exp.a

119.101 124.585 116.314 119.230 122.348 118.423 122.551 115.084 122.365 117.376 124.427 118.121 121.159 119.063 119.777 120.564 118.746 120.688 120.076 111.147 106.056 111.151 109.286 109.771 109.340 117.770 116.662 125.535

119.092 124.568 116.341 120.348 122.330 117.322 121.039 114.917 124.043 117.619 126.830 115.551 121.742 118.614 119.644 120.159 119.064 120.777 118.658 111.164 105.665 111.164 109.524 109.711 109.525 118.722 117.019 124.259

120.7

120.8

119.9

121.4

118.5

288

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

Table 3 Definition of internal coordinates of 4-bromo-3-nitroanisole. No(i)

Symbol

Type

Definitiona

Stretching 1–6 7–8 9–11 12–14 15 16–17 18

pi qi ri si ti ui

CAC CAO CAH(methyl) CAH(aro) CAN NAO CABr

C1AC2, C2AC3, C3AC4, C4AC5, C5AC6, C6AC1 C1AO7, C8AO7 C8AH9, C8AH10, C8AH11 C2AH12, C5AH17, C6AH18, C3AN13 N13AO14, N13AO15 C4ABr16

Ring CACAO CAH(methyl) HACAH CAH(aro) CACAN CANAO OANAO CACABr

C1AC2AC3, C2AC3AC4, C3AC4AC5, C4AC5AC6, C5AC6AC1, C6AC1AC2 C2AC1AO7, C6AC1AC7 O7AC8AH9, O7AC8AH10, O7AC8AH11 H9AC8AH10, H9AC8AH11, H10AC8AH11 C1AC2AH12, C3AC2AH12, C4AC5AH17, C6AC5AH17, C5AC6AH18, C1AC6AH18 C2AC3AN13, C4AC3AN13 C3AN13AO14, C3AN13AO15 O14AN13AO15 C3AC4ABr16, C5AC4ABr16

CAH CAN CANO2 CABr CAH tRing CAO CAO

H12AC2AC1AC3, H17AC5AC4AC6, H18AC6AC5AC1 N13AC3AC2AC4 C3AN13AO14AO15 Br16AC4AC5AC3 C1AO7AC8A(H9, H10, H11) C1AC2AC3AC4, C2AC3AC4AC5, C3AC4AC5AC6, C4AC5AC6AC1, C5AC6AC1AC2, C6AC1AC2AC3 O7AC1AC6AC2 C8AO7AC1AC2(C6)

vi

In-plane bending 19–24 25–26 27–29 30–32 33–38 39–40 41–42 43 44–45

ai bi ki ki hi

Ci

pi ei ui

Out-of-plane bending 46–48 ri 49 xi 50 si 51 Wi 52 qi 53–58 li 59 Di 60 Di a

For numbering of atoms refer Fig. 1.

Table 4 Definition of local symmetry coordinates of 4-bromo-3-nitroanisole.

a

No(i)

Symbola

Definition

1–6 7–8 9 10 11 12–14 15 16 17 18 19 20 21 22 23 24 25 26 27 28–30 31 32 33 34 35 36–38 39 40 41 42 43 44 45 46–47 48

CAC CAO CH3symd CH3asymd CH3symd CAH(aro) CAN NO2ss NO2as CABr Rtrigd Rsymd Rasymd dCAO CH3 sb CH3 ipb CH3 opb CH3 ipr CH3 opr dCAH dCAN NO2 scis NO2 rock NO2 twist dCABr cCAH cCAN cCANAO cCABr CH3 twist tRtrigd tRsymd tRasymd cCAOAC NO2 wag

p1, p2, p3, p4, p5, p6 q7, q8 p (r9 + r10 + r11)/ 3 p (2r9  r10  r11)/ 6 p (r10  r11)/ 2 s12, s13, s14 t15 p (u16 + u17)/ 2 p (u16  u17)/ 2

v18

p (a19  a20 + a21  a22 + a23  a24)/ 6 p (a19  a20 + 2a21  a22 + a23 + 2a24)/ 12 p (a19  a20 + a22  a23)/ 2 p (b25  b26)/ 2 p (k27  k28  k29 + k30 + k31 + k32)/ 6 p (k30  k31 + 2k32)/ 6 p (k30  k31)/ 2 p (2k27  k28  k29)/ 6 p (k28  k29)/ 2 p p p (h33  h34)/ 2, (h35  h36)/ 2, (h37  h38)/ 2 p C(C39  C40)/ 2 p (2e43  p41  p42)/ 6 p (p41  p42)/ 2 p (p41 + p42)/ 2 p (u44  u45)/ 2 r46, r47, r48

x49 s50 W51

q52 p (l53  l54 + l55  l56 + l57  l58)/ 6 p (l53  l55 + l56  l58)/ 2 p (l53 + 2l54  l55  l56 + 2l57  l58)/ 12 D59, D60 T61

For numbering of atoms refer Fig. 1.

notwithstanding the level of calculations, it is customary to scale down the calculated harmonic frequencies in order to develop the agreement with the experiment. The scaled calculated frequencies minimize the root-mean square difference calculated frequencies minimize the root-mean square difference definite identifications. CAH vibrations The aromatic structure shows the presence of CAH stretching vibration in the region 3100–3000 cm1, which is the characteristic region for the prepared recognition of CAH stretching vibration [27]. In this region, the bands are not affected appreciably by the nature of the substituent. The three expected CAH stretching vibrations correspond to stretching modes of C2AH, C5AH and C6AH units. Therefore in our present work, the FT-IR bands observed at 3091, 3015 cm1 and the FT-Raman bands at 3105, 3026 and 2974 cm1 are assigned to CAH stretching vibrations. The scaled vibrations by B3LYP/6-311++G (d,p) level shows very good agreement with recorded FT-Raman spectrum as well as the literature data. The CAH in-plane and out-of-plane bending vibrations generally lie in the region 1300–1000 cm1 and 1000–675 cm1 [28,29], respectively. In accordance with above literature data, the medium strong band observed in FT-IR spectrum at 1288 cm1 and the weak and very weak bands observed in FT-Raman at 1270, 1419 and 1511 cm1 are assigned to CAH in-plane bending vibrations. They show good agreement with the theoretically computed B3LYP/6-311++G (d,p) method. The very weak bands observed at 891 and 1030 cm1 in the FT-IR spectrum and the weak band observed at 934 cm1 in the FT-Raman are assigned to CAH out-of-plane bending vibration for BNA. The theoretically computed wave number for this mode falls within the range at 890, 932 and 1030 cm1 (mode nos. 28, 27 and 25) by B3LYP/6-311++G (d,p) method.

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

289

(a)

Transmittance (%)

(b)

(c)

4000

3500

3000

2500

2000

1500

1000

400

-1

Wavenumber (cm ) Fig. 2. (a) Experimental and theoretical, (b) HF/6-311++G (d,p), and (c) B3LYP/6-311++G (d,p) FT-IR and simulated spectrum of 4-bromo-3-nitroanisole.

CAC vibrations The ring C@C and CAC stretching vibrations, known as semicircle stretching usually occurs in the region 1400–1625 cm1 [30– 32]. The C@C stretching vibrations of the present compound are observed at 1348 cm1 in the FT-IR spectrum and 1622 and 1608 cm1 in FT-Raman spectrum. In our present study, the bands for CAC stretching vibrations are observed at 1227, 818 cm1 and 1230, 1145, 816 cm1 respectively in FT-IR and FT-Raman spectra. All the bands lie in the expected range when compared to the literature values. The CCC in-plane bending vibrations observed at 1095, 743, 332 cm1 and the out-of-plane bending vibrations appeared at 762, 566 and 447 cm1. These assignments are in good agreement with the literature [33,34]. These observed frequencies show that, the substitutions in the ring to some extend affect the ring modes of vibrations. The theoretically computed value by B3LYP/6-311++G (d,p) methods are in agreement with experimental values. CABr vibrations Strong characteristic absorption due to the CABr stretching vibration is observed [35–38] with the position of the band being influenced by neighboring atoms or groups, the smaller the halide atom, the greater the influence of the neighbor. Bands of weak to medium intensity are also observed for the CABr stretching vibrations. According to these early reports [39,40], the inductive effect of the bromine withdrawing electron from CABr bond. The

vibrations belonging to the bond between the ring and the bromine atom are important as mixing of vibrations are possible due to the presence of heavy atoms. The CABr stretching vibration gives generally strong band in the region 650–485 cm1. In the present study, a strong band observed at 621 cm1 in FT-IR and a weak band observed at 618 cm1 in FT-Raman spectrum are assigned to CABr stretching. The bands observed at 509 cm1 and 340 cm1 are assigned to CABr in-plane and out-plane bending vibrations respectively. The theoretically computed value by B3LYP/6-311++G (d,p) method for CABr out-of-plane bending (scaled) is exactly coincides with experimental value. This shows that the other vibrations can hold back the CABr vibrations due to its weak force constant [41]. The influence of other substitution on CABr stretching and deformation bands is significant in this compound. Methyl group vibrations The assignments of methyl group vibration make a significant contribution to the title molecule spectra. The presence of CAH vibrations ensures that the place of methyl group in benzene ring. For OACH3 compound, the CAH asymmetric and symmetric stretching vibrations appear in the range 2860–2935 cm1 and 2825–2870 cm1, respectively [42,43]. The FT-IR bands are assigned at 2961, 2891 cm1 and 2828 cm1 for asymmetric and symmetric CH3 stretching vibrations of the methyl group in BNA. The first band is slightly pulled up to the highest region which may be due to the mesomeric effect. The theoretically computed

290

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

(a)

Raman intensity

(b)

(c)

3500

3000

2500

2000

1500

1000

500

100

-1

Wavenumber (cm ) Fig. 3. (a) Experimental and theoretical, (b) HF/6-311++G (d,p), and (c) B3LYP/6-311++G (d,p) FT-Raman and simulated spectrum of 4-bromo-3-nitroanisole.

frequencies by B3LYP/6-311++G (d,p) shows an excellent agreement with experimental and literature values. The asymmetric deformation of CH3 group is usually observed at around 1450 cm1 for methyl substituted benzenes [44]. As expected, medium strong intensity band appeared at 1470 cm1 in FT-IR spectrum is due to CH3 asymmetric deformation vibration. The theoretically calculated values by B3LYP/6-311++G (d,p) coincide very well with the experimental value. The CAH in-plane bending vibrations have been assigned at 1495, 1435 and 1205 cm1 and CAH out-of-plane bending vibrations identified at 1199 and 220 cm1. These assignments are validated by the reported literature [45,46]. OACH3 vibrations The OACH3 stretching mode is normally assigned in the region 1000–1100 cm1 [47–49] for anisole and its derivatives. In this compound, a medium strong band is found at 1002 cm1 for OACH3 stretching vibration. The theoretically computed value by B3LYP/6-311++G (d,p) method for OACH3 stretching is approximately coincides with FT-IR experimental and literature values. The CAOACH3 angle bending mode is assigned at 310 cm1 for anisole [50]. Ramana Rao et al. [51] have propsed assignment for this mode in the region 300–670 cm1 for anisole and its derivatives. In accordance with above, a band is assigned to the theoretically calculated value by B3LYP/6-311++G (d,p) at 241 cm1 as CAOACH3 angle bending mode, which exactly coincides with the 242 cm1

band observed in the FT-Raman spectra. Varsanyi [52] has proposed assignment for out-of-plane mode of the CAOACH3 group at 100 cm1 for anisole. In the title molecule, the CAOACH3 outof-plane bending vibration is assigned at 117 cm1. According to the literature, this assignment is moderately agreed. Nitro group vibrations The nitro group compounds are readily identified by asymmetric and symmetric stretching bands. The asymmetric and symmetric bands are normally observed in the regions 1540–1614 cm1 and 1320–1390 cm1 respectively [53]. In BNA, two very strong bands are found at 1563 and 1351 cm1 which is attributed to NO2 asymmetric and symmetric stretching vibrations, respectively. In the aromatic nitro compound, a weak to medium intensity band is observed in the region 590–500 cm1 [54] due to the in-plane bending vibration of NO2 group. The out-of-plane vibration of NO2 contributes to several modes in the low frequency region [55]. In this study, two bands observed at 829 cm1 and 486 cm1 in the FT-Raman spectrum are assigned to NO2 scissoring and rocking vibrations, respectively. These vibrations are in line with the literature. CAN and CAO vibrations The CAN stretching frequency is a rather hard job since there are problems in identifying these frequencies from other vibrations. The CAN stretching absorption for aromatic amines

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

291

Table 5 Calculated vibrational frequencies (cm1) and assignments of 4-bromo-3-nitroanisole based on HF/6-311++G (d,p) and B3LYP/6-311++G (d,p) methods. Modes

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Species

A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A0 A00 A0 A0 A0 A0 A0 A0 A0 A00 A0 A0 A0 A0 A00 A0 A00 A00 A0 A0 A00 A0 A0 A00 A0 A0 A00 A0 A00 A0 A0 A00 A0 A00 A00 A00 A00 A00

Observed frequencies (cm1)

Calculated frequencies (cm1)

Vibrational assignments/TED(%)

HF/6-31++G (d,p)

B3LYP/6-31++G (d,p)

FT-IR

FT-Raman

Unscaled

Scaled

Unscaled

Scaled

3091(vw) 3015(w)

3105(vw) 3026(vw) 2974(vw)

3402 3373 3356 3297 3237 3172 1822 1785 1755 1656 1644 1628 1623 1606 1542 1439 1386 1318 1299 1292 1280 1237 1198 1172 1117 1092 1036 899 937 909 782 753 717 643 550 525 455 425 369 349 272 255 183 167 161 128 62 50

3110 3034 2982 2970 2903 2836 1627 1616 1571 1521 1497 1474 1438 1425 1357 1348 1289 1236 1212 1201 1192 1150 1126 1096 1033 1004 938 889 830 818 765 745 620 568 512 490 449 371 343 330 246 231 166 159 146 126 59 45

3333 3298 3194 3146 3078 3015 1642 1619 1590 1527 1503 1495 1474 1426 1378 1365 1301 1258 1267 1236 1195 1165 1127 1112 1035 1004 939 894 838 818 780 748 653 582 503 489 449 391 346 339 253 232 172 160 148 127 62 48

3090 3019 2970 2963 2897 2830 1622 1605 1561 1510 1495 1472 1435 1420 1353 1348 1288 1232 1207 1196 1187 1143 1121 1094 1030 997 932 890 829 818 763 741 618 566 507 482 445 365 340 333 241 228 165 157 145 125 60 47

2961(w) 2891(w) 2828(w) 1622(w) 1608(s) 1563(vs) 1511(w) 1495(vw) 1470(ms) 1435(vw) 1419(vw) 1351(vs) 1348(s) 1288(ms) 1227(s) 1205(vw) 1199(vw)

1270(w) 1230(s)

1189(w) 1145(vw) 1121(w) 1095(w) 1030(vw) 1002(ms) 934(w) 891(vw) 818(vw)

621(s)

829(vw) 816(w) 762(w) 743(vw) 618(w) 566(s)

509(vw) 486(vw) 447(w) 367(vw) 340(vw) 332(vw) 242(vw) 220(vw) 167(vw)

117(ms)

mCH(99) mCH(99) mCH(99) CH3ass(95) CH3ass(94) CH3ss(96) mCC(58), dCH(30), dCN(10) mCC(52), NO2ass(28) NO2ass(58), mCC(17), dCH(12), dCO(10) dCH(65), mCC(18), CH3ipb(12) CH3ipb(85), dCH(10) CH3opb(84) CH3sb(88), dCH(10) dCH(65), mCC(28) NO2ss(79), mCN(18) mCC(72), mCO(11), mCBr(10) dCH(85), mCO(10) mCC(84), mCO(12) CH3ipr(82), dCH(10) CH3opr(79) mCN(78), mCC(10) mCC(76), mCN(18) mCO(72), mCN(12), Ringipb(10) Ringbreathing(88), mCBr(10) cCH(88) mCO(76), mCH(12) cCH(85) cCH(86) NO2sci(60), Ringipb(18) mCC(76), cCN(10) Ringopb(69), mCBr(18) Ringipb(68) mCBr(58), Ringipb(22), dCN(12) Ringopb(53), cCN(12) dCBr(58), Ringipb(23) NO2rock(76), mCC(12) Ringopb(52), cCN(26), cCO(12) dCN(56), Ringipb(30), dCO(12) cCBr(49), Ringopb(20) Ringipb(59), dCN(18), dCH(11) dCO(66), dCH(21) CH3twist(67), cCN(20) dCO(68), dCH(18) NO2wag(58), Ringopb(22) cCN(49), cCO(17) cCO(60), mCBr(12) cCO(56), cCH(18), cCBr(10) NO2twist(68)

s: Strong; vs: very strong; ms: medium strong; w: weak; vw: very weak; ss: symmetric stretching; as: asymmetric stretching; d: in-plane bending; c: out-of-plane bending; t: torsion; R: Ring; wag: wagging; sci: scissoring; twist: twisting; m: stretching; ipr: in-plane rocking; opr: out-plane rocking.

are identified in the region 1382–1266 cm1 [56]. In the present study, the CAN stretching vibration is observed at 1189 cm1. According to the literature, this band is more deviated since the CAN bond is in between ring and NO2. Consequently, the CAN in-plane bending vibration is found at 367 cm1. These vibrations are in order with the literature. A strong band is observed in the region 1300–1200 cm1 due to CAO stretching vibrations for substituted phenols [57]. In the present case, a weak band at 1121 cm1 is assigned to CAO stretching vibration. The CAO in-plane pending vibration is found at 167 cm1. These assignments are also supported by the literature [58].

percentage of the electron density. A useful aspect of the NBO method is that it gives information about interactions in both filled and virtual orbital spaces that could enhance the analysis of intraand inter-molecular interactions. The second-order Fock matrix was carried out to evaluate the donor–acceptor interactions in the NBO analysis [59]. The interactions result is a loss of occupancy from the localized NBO of the idealized Lewis structure into an empty non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy E(2) associated with the delocalization i ? j is estimated as

Eð2Þ ¼ DEij ¼ qi Natural bond orbital study Natural bond orbital (NBO) analysis provides the most accurate possible ‘natural Lewis structure’ picture of u, because all orbital details are mathematically chosen to include the highest possible

Fði; jÞ2 ej  ei

where qi is the donor orbital occupancy, ei and ej are diagonal elements and F(i,j) is the off diagonal NBO Fock matrix element. Natural bond orbital analysis provides an efficient method for studying intra- and inter-molecular bonding and interaction

292

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

Table 6 NBO results showing of Lewis and non-Lewis orbitals of 4-bromo-3-nitroanisole. Bond (A–B)

r(C1AC2) r(C1AC6) r(C1AO7) r(C2AC3) r(C3AN13) r(C4ABr16) r(O7AC8) r(N13AO14) r(N13AO15) LP(2) O7 LP(3) O15 LP(3) Br16

ED/energy (a.u.) 1.97512 0.02580 1.97831 0.02131 1.98898 0.03228 1.96392 0.02321 1.98718 0.11418 1.98019 0.03375 1.99302 0.00546 1.99527 0.05355 1.99545 0.05416 1.85750 1.45327 1.90681

EDA (%)

EDB (%)

49.29

50.71

49.61

50.39

33.22

66.78

49.06

50.94

37.65

62.35

51.79

48.21

68.17

31.83

48.80

51.20

48.84

51.16

– – –

– – –

among bonds, and also provides a convenient basis for investigating charge transfer or conjugative interaction in molecular systems. Some electron donor orbital, acceptor orbital and the interacting stabilization energy resulted from the second-order micro-disturbance theory are reported [60,61]. NBO analysis has been performed on the molecule at the DFT/B3LYP/6-311++G (d,p) level in order to elucidate the intra-molecular, rehybridization and delocalization of electron density within the molecule. Delocalization of electron density between occupied Lewis-type (bond or lone pair) NBO orbitals and formally unoccupied (anti-bond or Rydberg) non-Lewis NBO orbitals correspond to a stabilizing donor–acceptor interaction. The corresponding results have been tabulated as shown in Table 6. The larger the E(2) value, the more intensive is the interaction between electron donors and electron acceptors, i.e. the more donating tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system. The possible intensive interactions are given in Table 7. In Table 6, r(N13AO14) orbital with 1.99527 electrons has 48.80% N13 character in a sp2.10 hybrid and has 51.20% O14 character in a sp2.78 hybrid. The sp2.10 hybrid on N has 67.63% p-character and the sp2.78 hybrid on O has 73.41% p-character in B3LYP/6311++G (d,p). The four coefficients, 0.6985, 0.7156, 0.6989 and 0.7152 are called polarization coefficients of BNA. The sizes of these coefficients show the importance of the two hybrids in the formation of the bond. In the title molecule the nitrogen has larger percentage of NBO and gives the larger polarization coefficient because it has the higher electro negativity. Similar results are found in all the r(N13AO15) and r(O7AC8) orbital’s. At the end of the table lone pairs are expected to the Lewis structure. Delocalization of the electron density between occupied Lewistype (bond or lone pair) NBO orbitals and formally unoccupied (antibond or Rydberg) non-Lewis NBO orbitals corresponding to a stabilizing donor–acceptor interaction. The energy of this interaction can be estimated by the second order perturbation theory. Table 7 lists the calculated second order interaction energies (E(2)) between the donor–acceptor orbital’s in BNA molecule with B3LYP/6-311++G (d, p) method. For the title molecule, high energy values are found in the range 3–171 kJ/mol, and the lone pair energy values found to be higher than 11.82 kJ/mol. This difference in interaction energies is due to inter- and intra-molecular interactions of the molecules.

NBO 1.68

0.7021(sp )c 0.7121(sp1.87)c 1.61 0.7098(sp )c 0.7044(sp1.87)c 3.14 0.5763(sp )c 0.8172(sp2.65)c 0.7004(sp1.85)c 0.7137(sp1.64)c 0.6136(sp3.12)c 0.7896(sp1.83)c 0.7196(sp3.38)c 0.6943(sp6.74)c 0.8257(sp2.68)o 0.5641(sp3.70)o 0.6985(sp2.10)n 0.7156(sp2.78)n 0.6989(sp2.09)n 0.7152(sp2.74)n Sp1.00 Sp1.00 Sp1.00

S (%)

P (%)

37.34 34.80 38.26 34.81 24.13 27.40 35.12 37.89 24.24 35.27 22.82 12.87 27.15 21.21 32.24 26.44 32.29 26.67 0.00 0.00 0.00

62.62 65.15 61.70 65.14 75.66 72.53 64.84 62.08 75.65 64.70 77.07 86.73 72.78 78.49 67.63 73.41 67.58 73.19 99.95 99.87 99.97

Table 7 Second-order perturbation theory analysis of Fock matrix in NBO basic corresponding to the intramolecular bonds of 4-bromo-3-nitroanisole. Donor (i)

Acceptor (j)

a (2)

r(C1AC2)

r (C1AC6) r⁄(C1AC2) r⁄(C1AC2) r⁄(C3AC4) r⁄(C4ABr16) r⁄(C1AC6) r⁄(C3AC4) r⁄(C2AC3) p⁄(C1AC2) p⁄(C5AC6) p⁄(N13AO14) r⁄(C3AN13) r⁄(C2AC3) r⁄(C1AO7) r⁄(C4ABr16) p⁄(C1AC2) p⁄(C3AC4) r⁄(C1AC2) p⁄(C1AC2) r⁄(C3AN13) r⁄(N13AO15) r⁄(C3AN13) r⁄(N13AO14) p⁄(N13AO14) p⁄(C3AC4)

3.74 3.76 3.71 6.29 4.75 3.95 4.07 5.62 17.69 17.23 20.16 3.80 3.75 4.41 5.17 20.62 21.38 4.34 23.46 15.38 19.86 14.94 19.61 171.11 11.82

r(C1AC6) r(C2AC3) r(C2AH12) r(C3AC4) p(C3AC4) r(C4AC5) r(C4ABr16) r(C5AC6)

p(C5AC6) r(C6AH18) LP(2) O7 LP(2) O14 LP(2) O15 LP(3) O15 LP(3) Br16 a b c

⁄

E

(kJ mol1)

b

E(j)  E(i) (a.u.)

1.28 1.00 1.28 1.27 0.82 1.10 1.08 1.30 0.30 0.31 0.17 1.01 1.19 0.99 0.81 0.28 0.26 1.09 0.32 0.56 0.77 0.56 0.77 0.15 0.28

c

F(i,j) (a.u.)

0.062 0.056 0.061 0.080 0.056 0.059 0.059 0.076 0.066 0.065 0.056 0.057 0.060 0.059 0.058 0.068 0.069 0.061 0.082 0.083 0.112 0.082 0.111 0.146 0.056

E(2) means energy of hyperconjugative interactions. Energy difference between donor and acceptor i and j NBO orbitals. F(i,j) is the Fock matrix element between i and j NBO orbitals.

Polarizability and hyperpolarizability The first-order hyperpolarizability (b0) of this novel molecular system and the related properties (b0, ao and Da) of BNA were calculated using B3LYP with 6-311++G (d,p) basis set, based on the finite field approach. In presence of an applied electric field, the energy of a system is a function of the electric field. The first hyperpolarizability is a third-rank tensor that can be described by a 3  3  3 matrix. The 27 components of the 30 matrix can be reduced to 10 components due to the Kleinman symmetry [62]. The components of b0 are defined as the coefficients in the Taylor series exponents the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion becomes.

293

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

E ¼ E0  la F a  1=2aab F a F b  1=6babc F a F b F c þ    where E0 is the energy of the unperturbed molecules, Fa is the field at the origin and la, aab and babc are the components of dipole moment, polarizability and the first-order hyperpolarizabilities respectively. The total static dipole moment (l), the mean polarizability (ao), the anisotropy of the polarizability (Da) and the mean first-order hyperpolarizability (b0), using the x, y, z components they are defined as follows: The total static dipole moment is

l¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðl2x þ l2y þ l2z Þ

The isotropic polarizability is

ao ¼

axx þ ayy þ azz

Parameters

Values

bxxx bxxy bxyy byyy bxxz byyz bxzz byzz bzzz First order hyperpolarizability Polarizibility Dipole moment

210.93 67.79 42.59 180.32 13.72 2.28 10.64 10.92 7.71 2.9727  1030 e.s.u. 1.044  1030 e.s.u. 2.3189 debye

3

The anisotropy polarizability is

" #1=2 ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 Da ¼ 2 The mean first-order hyperpolarizability is

b0 ¼

Table 8 Theoretical polarizability (a)(e.su.), first order hyperpolarizability (b)(e.su.) along with theoretical dipole moment (l) (debye) of 4-bromo-3-nitroanisole using DFT/ B3LYP/6-311++G (d,p) method.

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðb2x þ b2y þ b2z Þ

where

bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ bxxy þ byzz bz ¼ bzzz þ bxxz þ byyz Since the values of the polarizabilities (a) and hyperpolarizability (b) of the Gaussian 09 output are reported in atomic units (a.u.), the calculated values have been converted into electrostatic units (e.s.u.) (1 a.u. = 8.639  1033 e.s.u.). The total molecular dipole moment, polarizability and first hyperpolarizability are 2.3189 debye, 1.0445  1030 e.s.u. and 2.9727  1030 e.s.u., respectively and are depicted in Table 8. Total dipole moment of title molecule is slightly higher than those of urea and first hyperpolarizability of title molecule is 8 times greater than those of urea (l and b of urea are 1.3732 debye and 0.37289  1030 e.s.u. obtained by B3LYP/6-311++G (d,p) method [63]). HOMO–LUMO analysis When we see the first hyperpolarizability value, there is an inverse relationship between first hyperpolarizability and HOMO– LUMO gap, allowing the molecular orbitals to overlap to have a proper electronic communication conjugation, which is a marker of the intra-molecular charge transfer from the electron donating group through the p-conjugation system to the electron accepting group [64,65]. Many organic molecules, containing conjugated p-electrons characterized by large values of molecular first hyperpolarizabilities were analyzed by means of vibrational spectroscopy [66,67]. In most cases, even in the absence of inversion symmetry, the strongest bands in the Raman spectrum are weak in the IR spectrum and vice versa. But the intra-molecular charge transfer from the donor to acceptor group through a single-double bond conjugated path can induce large variations of both the molecular dipole moment and the molecular polarizability, making IR and Raman activity strong at the same time. The most important orbitals in a molecule are the frontier molecular orbitals, called HOMO and LUMO. These orbitals determine the way the molecule interacts with other species. The frontier orbital gap helps to characterize the chemical reactivity and kinetic stability of the molecule. A

Table 9 Energy gap values (eV) of 4-bromo-3-nitroanisole. Parameter

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

Etotal (Hartree) EHOMO (eV) ELUMO (eV) DEHOMO  ELUMO gap (eV) EHOMO1 (eV) ELUMO+1 (eV) DEHOMO1ELUMO+1 gap (eV) EHOMO2 (eV) ELUMO+2 (eV) DEHOMO2ELUMO+2 gap (eV)

3124.68850 7.08095 2.92114 4.15981 7.13537 1.29581 5.83956 8.27090 0.79620 7.47470

molecule with a small frontier orbital gap is more polarizable and is generally associated with a high chemical reactivity, low kinetic stability and is also termed as soft molecule [68]. The frontier molecular orbitals play an important role in the electric and optical properties [69]. The conjugated molecules are characterized by a small highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) separation, which is the result of a significant degree of intramolecular charge transfer from the end-capping electron–donor groups to the efficient electron– acceptor groups through p-conjugated path [70]. The HOMO represents the ability to donate an electron, LUMO as an electron acceptor represents the ability to obtain an electron. The HOMO and LUMO energy calculated by B3LYP/6-311++G (d,p) method is shown below. This electronic absorption corresponds to the transition from the ground to the first excited state and is mainly described by one electron excitation from the HOMO to the LUMO. While the energy of the HOMO is directly related to the ionization potential, LUMO energy is directly related to the electron affinity. Energy difference between HOMO and LUMO orbital is called as energy gap that is an important stability for structures [71] and is given in Table 9. The plots of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) are shown in Fig. 4. HOMO is localized on the central ring and has no contribution from the substitution groups such as methyl and bromine. LUMO is quite localized on the central ring and has contribution from the substituted electronegative bromine atom. The energy gap between HOMO and LUMO is 4.15981 eV, which shows that charge transfer may be taking place from the ring to bromine atom.

Molecular electrostatic potentials (MEP) Molecular electrostatic used extensively for interpreting potentials have been and predicting the reactive behavior of a wide variety of chemical system in both electrophilic and nucleophilic reactions, the study of biological recognition processes and

294

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

Fig. 4. The atomic orbital composition of the frontier molecular orbital for 4-bromo-3-nitroanisole.

hydrogen bonding interactions [72]. V(r), at a given point r(x,y,z) in the vicinity of a molecule, is defined in terms of the interaction energy between the electrical charge generated from the molecule electrons and nuclei and positive test charge (a proton) located at r. Unlike many of the other quantities used at present and earlier as indices of reactivity, V(r) is a real physical property that can be determined experimentally by diffraction or by computational methods. For the systems studied the MEP values were calculated as described previously, using the equation [73]:

VðrÞ ¼

X

ZA  jRA  rj

Z

qðr0 Þ 0 dr jr 0  rj

where the summation runs over all the nuclei A in the molecule and polarization and reorganization effects are neglected. ZA is the

charge of the nucleus A, located at RA and q(r0 ) is the electron density function of the molecule. To predict reactive sites for electrophilic and nucleophilic attack for the investigated molecule, molecular electrostatic potential (MEP) was calculated at B3LYP/6-311++G (d,p) optimized geometries. In the majority of the MEPs, while the maximum negative region which preferred site for electrophilic attack indications as red color, the maximum positive region which preferred site for nucleophilic attack symptoms as blue color. 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 color grading and is very useful in research of molecular structure with its physiochemical property relationship. The resulting surface simultaneously displays molecular size and

295

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

C1 C2 C3 C4 C5 C6 O7 C8 H9 H10 H11 H12 N13 O14 O15

Fig. 5. 3D-molecular electrostatic potential map of 4-bromo-3-nitroanisole.

Table 10 The electrostatic potential values with atomic charge of 4-bromo-3-nitroanisole based on B3LYP level. Atom

Charge

Electrostatic potential (a.u.)

C1 C2 C3 C4 C5 C6 O7 C8 H9 H10 H11 H12 N13 O14 O15 Br16 H17 H18

0.506880 0.485623 0.546301 0.618594 0.296031 0.412543 0.381549 0.027750 0.063950 0.089731 0.063950 0.168988 0.618514 0.358895 0.442670 0.054213 0.066059 0.197481

14.635241 14.692736 14.648267 14.645321 14.689643 14.691594 22.247007 14.672119 1.084707 1.082539 1.084707 1.055050 18.088858 22.276444 22.272668 175.229809 1.064066 1.062682

shape and electrostatic potential value. In the present study, 3D plots of molecular electrostatic potential (MEP) of BNA has been drawn in Fig. 5. The MEP is a plot of electrostatic potential mapped onto the constant electron density surface. 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 0.04900 a.u. (deepest red) and 0.04900 a.u. (deepest blue) in compound, where blue shows the strongest attraction and red shows the strongest repulsion. Regions of negative V(r) are usually associated with the lone pair of electronegative atoms. As we seen from the MEP map of the title molecule, while regions having the negative potential are over the electronegative atoms (nitrogen atom, bromine atom and oxygen atom with collection NO2 group). The most negative V(r) value is associated with Br16 of BNA. Thus, it would be predicted that an electrophile would preferentially attack BNA molecule at the Br16 position. In

Table 11 Mullikan’s atomic charges of 4-bromo-3-nitroanisole based on HF and B3LYP levels. Atom no.

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

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

C1 C2 C3 C4 C5 C6 O7 C8 H9 H10 H11 H12 N13 O14 O15 Br16 H17 H18

0.480154 0.429456 0.517726 0.911938 0.173856 0.669231 0.240106 0.345311 0.153560 0.190929 0.157708 0.278317 0.030849 0.041933 0.053044 0.160018 0.294657 0.233966

0.386012 0.325870 0.807489 1.036745 0.149006 0.913968 0.165935 0.165935 0.153917 0.197413 0.153917 0.277339 0.064813 0.000015 0.004028 0.033352 0.235961 0.200083

addition, we found the positive regions over the hydrogen atoms of methyl group of BNA molecule and indicating that these sites can be the most probably involved in nucleophilic processes. However, the H atoms in the ring have higher values than on the H atoms in the CH3 group. Red and blue areas in the MEP map refer to the regions of negative and positive potentials and correspond to the electron rich and electron-poor regions, respectively, whereas the green color signifies the neutral electrostatic potential. The MEP surface provides necessary information about the reactive sites. The theoretically calculated eletrostatic potential with charges as shown in Table 10. Mulliken atomic charges The atomic charge in molecules is fundamental to chemistry. For instance, atomic charge has been used to describe the processes of electro negativity equalization and charge transfer in chemical reactions [74,75], and to model the electrostatic potential outside molecular surfaces [76–78]. Mulliken atomic charges

296

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

80

Table 12 Thermodynamic properties at different temperatures at the B3LYP/6-311++G (d,p) level for 4-bromo-3-nitroanisole. T (K)

C 0p;m

100 200 300 400 500 600 700

G0m (kcal mol1)

S0m (kcal mol1)

12.199667 23.040047 33.125519 42.667497 50.883910 57.593414 63.009241

5.544826 11.663422 17.140872 22.350872 27.261347 31.777472 35.865988

3.590077 9.367332 15.143859 20.794385 26.315945 31.691885 36.902890

9.134903 21.030754 32.284731 43.145256 53.577292 63.469357 72.768886

70 60

−

−

(cal mol1 K1)

DH0m (kcal mol1)

50 40 30 20

−

0 -5

10

-10

0

100

200

300

400

500

600

700

-15 Fig. 8. Correlation graph of entropy with temperature of 4-bromo-3-nitroanisole.

-20 -25

40 -30 35 −

-35 30

-40 100

200

300

400

500

600

700

Fig. 6. Correlation graph of Gibb’s energy with temperature of 4-bromo-3nitroanisole.

25 20 15 10

60

5

−

70

−

100

200

300

400

500

600

700

50 Fig. 9. Correlation graph of enthalpy with temperature of 4-bromo-3-nitroanisole.

40

30

20

10 100

200

300

400

500

600

700

is obtained for C4 which is a carbon present in the Br atom. The charge on H12 atom has the maximum magnitude of 0.277339 among the hydrogen atoms present in the molecule at B3LYP/6311++G (d,p) level of theory. However all the hydrogen atoms exhibit net positive charges and these magnitudes are changing between 0.153917 and 0.277339. The presence of large negative charge on C6 and C3 atom and net positive charge on H atom may suggest the formation of intramolecular interaction in solid forms [79].

Fig. 7. Correlation graph of heat capacity with temperature of 4-bromo-3nitroanisole.

Thermodynamic properties

calculated at the HF and B3LYP/6-311++G (d,p) methods are collected in Table 11. It is worthy to mention that C2, C4 and C5 atoms of BNA exhibit positive charge, while C1, C3, C6, C8 atoms exhibit negative charges and C6 has a maximum negative charge value of about 0.913968. The maximum positive atomic charge

On the basis of vibrational analysis, the statically thermodynamic functions: heat capacity (C 0p;m ), enthalpy changes (DH0m ), Gibb’s free energy (G0m ) and entropy (S0m ) for the title molecule were obtained from the theoretical harmonic frequencies and listed in Table 12. From the Table 12, it can be observed that these thermodynamic functions are increasing with temperature ranging from

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

100 to 700 K due to the fact that the molecular vibrational intensities increase with temperature. The correlation equations between heat capacity, Gibb’s free energy, entropy, enthalpy changes and temperatures were fitted by quadratic formulas and the corresponding fitting factors (R2) for these thermodynamic properties are 0.9994, 1.0000, 1.0000 and 1.0000, respectively. The corresponding fitting equations are as follows and the correlation graphics of those shown in Figs. 6–9.

C 0p;m ¼ 0:489 þ 0:129T  6:0  105 T 2 H0m ¼ 0:751 þ 0:065T  2:0  105 T 2 G0m ¼ 2:435  0:060T þ 6:0  105 T 2

ðR2 ¼ 0:9994Þ ðR2 ¼ 1:0000Þ

ðR2 ¼ 1:0000Þ

S0m ¼ 3:187 þ 0:125T  2:0  105 T 2

ðR2 ¼ 1:0000Þ

All the thermodynamic data supply helpful information for the further study on the BNA. 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 thermo chemical field. Notice: all thermodynamic calculations were done in gas phase and they could not be used in solution. Conclusion In this study, the spectroscopic properties of the compound were examined by FT-IR and FT-Raman techniques. Various quantum chemical calculations help us to identify the structural, conformational and symmetry properties of the molecule. The optimized geometric parameters (bond lengths and bond angles) were theoretically determined at HF/6-311++G (d,p) and B3LYP/ 6-311++G (d,p) levels of theory and compared with X-ray results. A comparison of the result of experimental and theoretical study gave us a full description of the geometry and vibrational properties of title molecule. Also HOMO and LUMO energy of 4-bromo3-nitroanisole in the ground state have been calculated by using density functional theory for O-trans structure. NBO result reflects the charge transfer within the molecule. The Mulliken charges and first order hyperpolarizability are determined. The thermodynamic functions of the 4-bromo-3-nitroanisole 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. The MEP map shows that the negative potential sites are on oxygen, nitrogen and bromine atoms as well as the positive potential sites are the hydrogen atoms in the amino group. We hope our paper will be helpful for the design and synthesis new materials. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2012.12.070. References [1] G.S. Hiers, F.D. Hager, Org. Synth. Collect. 1 (1941) 58–60. [2] M. Rumi, G. Zerbi, J. Mol. Struct. 509 (1999) 111–115. [3] H. Fiege, H.-W. Voges, T. Hamamoto, S. Umemura, T. Iwata, H. Miki, Y. Fujita, H.-J. Buysch, D. Garbe, W. Paulus, Ullmann’s Encyclopedia of Industrial Chemistry, Wiley, Weinheim, 2002. [4] M. Naoki, N. Shusuke, T. Satoshi, E. Takeaki, J. Opt. Com. 260 (2006) 25–29. [5] J.C. Espin, J. Tudela, F. Garcia-Canovas, Anal. Biochem. 259 (1998) 118–126. [6] J.P. Gordon, R.C.C. Leite, R.S. Moore, S.P.S. Porte, J.R. Whinnery, J. Appl. Phys. 36 (1965) 3–8. [7] S.J. Sheldon, L.V. Knight, J.M. Thorne, Appl. Opt. 21 (1982) 1663–1669.

297

[8] F. Jurgensen, W. Schroer, Appl. Opt. 34 (1995) 41–50. [9] V. Krishnakumar, N. Prabavathi, Spectrochim. Acta Part A 74 (2009) 154–161. [10] T. Prabhu, S. Periandy, S. Ramalingam, Spectrochim. Acta Part A 83 (2011) 8– 16. [11] I.F. Shishkov, L.V. Khristenko, N.M. Karasev, L.V. Vilkov, H. Oberhammer, J. Mol. Struct. 873 (2008) 137–141. [12] S. Ramalingam, S. Periandy, Spectrochim. Acta Part A 78 (2011) 835–843. [13] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, Gaussian 2009, Revision A.02 Gaussian, Inc., Wallingford CT, 2009.. [14] T. Sundius, J. Mol. Struc. 218 (1990) 321326; MOLVIB: A Program for Harmonic force field calculations. QCPE Program No. 807 (2002). [15] T. Sundius, Vib. Spectrosc. 29 (2002) 89–95. [16] A. Frisch, A.B. Neilson, A.J. Holder, GAUSSVIEW User Manual, Gaussian Inc., Pittsburgh, CT, 2009. [17] P.L. Polavarapu, J. Phys. Chem. 94 (1990) 8106–8112. [18] G. Keresztury, BT Raman spectroscopy. Theory, in: J.M. Chalmers, P.R. Griffiths (Eds.), Handbook of Vibrational Spectroscopy, vol. 1, John Wiley & Sons Ltd., 2002, p. 71. [19] G. Keresztury, S. Holly, J. Varga, G. Besenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta 49A (1993) 2007–2026. [20] M. Silverstein, G.C. Basseler, C. Morill, Spectrometric Identification of Organic Compounds, Wiley, New York, 1981. [21] N. Sundaraganesan, S. Kalaichelvan, C. Meganathan, B. Dominic Joshua, J. Cornard, Spectrochim. Acta Part A 71 (2008) 898–906. [22] H. Mollendal, S. Gundersen, M.A. Tafipolsky, H.V. Volden, J. Mol. Struct. 444 (1998) 46–47. [23] S. Samdal, T.G. Strand, M.A. Tafipolsky, L.V. Vilkov, M.V. Popik, H.V. Volden, J. Mol. Struct. 435 (1997) 89–99. [24] D. Xiao, D. Yu, X. Xu, Z. Yu, Y. Du, Z. Gao, Q. Zhu, C. Zhang, J. Mol. Struct. 882 (2008) 56–62. [25] M.A. Palafox, J.L. Nunez, M. Gil, J. Mol. Struct. (Theochem.) 593 (2002) 101– 106. [26] G.D. Lister, J.K. Tyler, J.K. Hog, N.W. Larsen, J. Mol. Struct. 23 (1974) 253–258. [27] V.K. Rastogi, M.A. Palafox, R.P. Tanwar, L. Mittal, Spectrochim. Acta Part A 58 (2002) 1987–2004. [28] V. Krishnakumar, N. Prabavathi, Spectrochim. Acta Part A 71 (2008) 449–457. [29] A. Altun, K. Golcuk, M. Kumru, J. Mol. Struct. (Theochem.) 155 (2003) 637–639. [30] V. Krishnakumar, R. John Xavier, Ind. J. Pure Appl. Phys. 41 (2003) 95–98. [31] D.N. Sathyanarayana, Vibrational Spectroscopy Theory and Applications, 2nd ed., New Age International (P) Limited Publisher, New Delhi, 2004. [32] N.P. Singh, R.A. Yadav, Ind. J. Phys. B 75 (4) (2001) 347–355. [33] R.L. Peesole, L.D. Shield, I.C. Mcwillam, Modern Methods of Chemical Analysis, Wiley, New York, 1976. [34] G. Socrates, IR and Raman Characteristics Group Frequencies Tables and Charts, 3rd ed., Wiley, Chichester, 2001. pp. 107–111. [35] D. Michalska, Spectrochim. Acta Part A 49 (1993) 303–307. [36] L.J. Bellamy, The Infrared Spectra of Complex Molecules, 3rd ed., Wiley, New York, 1975. [37] C.J. Pouchert, The Aldrich Library of FT-IR spectra, Aldrich Chemicals Co., Milwaukee, WI, 1985. [38] S. Higuchi, Spectrochim. Acta Part A 30 (1974) 463–467. [39] D.H. Wiffen, Spectrochim. Acta 7 (1955) 253–256. [40] V. Sortur, J. Yenagi, J. Tonannavar, V.B. Jadhav, M.V. Kulkarni, Spectrochim. Acta Part A 71 (2008) 688–694. [41] J.H. Risgin, Fluorocarbons and Related Compounds, vol. II, Academic Press, New York, 1954. pp. 449–452. [42] N. Sundaraganesan, K. Sathesh Kumar, C. Meganathan, B. Dominic Joshua, Spectrochim. Acta Part A 65 (2006) 1186–1196. [43] N. Sundaraganesan, M. Priya, C. Meganathan, B. Dominic Joshua, J. Cornard, Spectrochim. Acta Part A 70 (2008) 50–59. [44] J.H.S. Green, D.J. Harrison, W. Kynoston, Spectrochim. Acta Part A 27 (1971) 807–810. [45] A. Altun, K. Golcuk, M. Kumru, J. Mol. Struct. (Theochem.) 625 (2003) 17–24. [46] J.R. Durig, M.M. Bergana, H.V. Phan, J. Raman Spectrosc. 22 (1991) 141–146. [47] W.J. Balfour, Spectrochim. Acta Part A 39 (1983) 780–795. [48] B. Vekkatram Reddy, G. Ramana Rao, Vib. Spectrosc. 6 (1994) 231–235. [49] V. Ashok Babu, B. Lakshmaiah, K. Sree Ramulu, G. Ramana Rao, Ind. J. Pure Appl. Phys. 25 (1987) 58–62. [50] W.B. Tzeng, K. Narayan, J.L. Lin, C.C. Tung, Spectrochim. Acta Part A 55 (1999) 153–157. [51] B. Lakshmaian, G. Ramana Rao, J. Raman Spectrosc. 20 (1989) 439–448. [52] G. Varsanyi, Vibrational Spectra of Benzene Derivatives, Academic Press, New York, 1969. [53] E.K. Meislich, H. Meislich, J. Sharefkin, 3000 Solved Problems in Organic Chemistry, vol. 2, McGraw-Hill, New York, 1993.

298

V. Balachandran, V. Karunakaran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 106 (2013) 284–298

[54] S. George, Infrared and Raman Characteristic Group Frequencies – Tables and Charts, third ed., Wiley, New York, 2001. [55] A. Kovacs, G. Keresztury, V. Izvekow, J. Chem. Phys. 253 (2000) 193–204. [56] M. Silverstein, G. Clayton Basseler, C. Morill, Spectrometric Identification of Organic Compounds, Wiley, New York, 1981. [57] A.J. Abkowicz-Bienko, D.C. Bienko, Z. Latajka, J. Mol. Struct. 552 (2000) 165– 175. [58] V. Krishnakumar, S. Seshadri, S. Muthunatesan, Spectrochim. Acta Part A 68 (2007) 811–816. [59] M. Szafran, A. Komasa, E. Bartoszak-Adamska, J. Mol. Struct. 827 (2007) 101107. [60] C. James, A. Amal Raj, R. Reghunathan, I.H. Joe, V.S. Jayakumar, J. Raman Spectrosc. 37 (2006) 13811392. [61] J.N. Liu, Z.R. Chen, S.F. Yuan, J. Zhejiang Univ. Sci. B6 (2005) 584591. [62] D.A. Kleinman, Phys. Rev. 126 (1962) 1977–1979. [63] Y.X. Sun, Q.L. Hao, W.X. Wei, Z.X. Yu, L.D. Lu, X. Wang, Y.S. Wang, J. Mol. Struct. (Theochem.) 904 (2009) 74–82. [64] M.C. Ruiz Delgado, V. Hernandez, J. Casado, J.T. Lopez Navarre, J.M. Raimundo, P. Blanchard, J. Roncali, J. Mol. Struct. 651–653 (2003) 151–158. [65] J.P. Abraham, D. Sajan, V. Shettigar, S.M. Dharmaprakash, I. Nemec, I.H. Joe, V.S. Jayakumar, J. Mol. Struct. 917 (2009) 27–36.

[66] T. Vijayakumar, I. Hubert Joe, C.P.R. Nair, V.S. Jayakumar, Chem. Phys. 343 (2008) 83–99. [67] M.A. Palafox, Int. J. Quantum Chem. 77 (2000) 661–684. [68] I. Fleming, Frontier Orbitals and Organic Chemical Reactions, John Wiley and Sons, New York, 1976. [69] T. Karakurt, M. Dinçer, A. Çetin, M. S ß ekerci, Spectrochim. Acta 77A (2010) 189–198. [70] C.H. Choi, M. Kertesz, J. Phys. Chem. A 101 (1997) 3823–3831. [71] D.F.V. Lewis, C. Ioannides, D.V. Parke, Xenobiotica 24 (1994) 401–408. [72] P. Politzer, J.S. Murray, Theoretical biochemistry and molecular biophysics: a comprehensive survey, vol. 2. Protein, in: D.L. Beveridge, R. Lavery (Eds.), Electrostatic Potential Analysis of Dibenzo-p-dioxins and Structurally Similar Systems in Relation to their Biological Activities, Adenine Press, Schenectady, NY, 1991 (Chapter 13). [73] P. Politzer, J. Murray, Theor. Chem. Acc. 108 (2002) 134–142. [74] K. Jug, Z.B. Maksic, in: Z.B. Maksic (Ed.), Theoretical Model of Chemical Bonding, Part 3, Springer, Berlin, 1991, p. 233. [75] S. Fliszar, Charge Distributions and Chemical Effects, Springer, New York, 1983. [76] P.E. Smith, J. Am. Chem. Soc. 113 (1991) 6029–6037. [77] J. Gao, J. Chem. Phys. 98 (1993) 1975–1981. [78] P. Cieplak, J. Comp. Chem. 12 (1991) 1232–1236. [79] L. Xiao-Hong et al., Comput. Theor. Chem. 969 (2011) 27–34.