Vibrational spectroscopy investigation using ab initio and density functional theory analysis on the structure of 3-aminobenzotrifluoride

Spectrochimica Acta Part A 67 (2007) 214–224

Vibrational spectroscopy investigation using ab initio and density functional theory analysis on the structure of 3-aminobenzotrifluoride N. Sundaraganesan a,∗ , S. Illakiamani a , C. Meganathan a , B. Dominic Joshua b a

b

Department of Physics (Engineering), Annamalai University, Annamalai Nagar 608 002, Tamil Nadu, India Department of Physics, Sri Aravindar Arts and Science College, Akasampet, Vanur District 605 111, Tamil Nadu, India Received 26 March 2006; accepted 3 July 2006

Abstract In this work, we will report a combined experimental and theoretical study on molecular and vibrational structure of 3-aminobenzotrifluoride. The FT-Raman and Fourier transform infrared spectra of 3-aminobenzotrifluoride (3ABTF) were recorded in the liquid phase. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, depolarization ratios, reduced masses were calculated by HF and density functional B3LYP method with the 6-31G(d,p) and 6-311G(d,p) basis sets. The scaled theoretical wavenumbers showed very good agreement with the experimental values. The thermodynamic functions of the title compound were also performed at HF/6-31G(d,p)/6-311G(d,p) and B3LYP/6-31G(d,p)/6-311G(d,p) levels of theory. A detailed interpretations of the infrared and Raman spectra of 3ABTF is reported. The theoretical spectrograms for FT-IR spectra of the title molecule have been constructed. © 2006 Elsevier B.V. All rights reserved. Keywords: FT-IR and FT-Raman spectra; Ab initio and DFT; 3-Aminobenzotrifluoride; Vibrational analysis

1. Introduction Derivatives of aminobenzotrifluoride have been the subject of investigation for many reasons. The derivatives of aminobenzotrifluoride have got wide applications, such as anti-bacterial agents, central, nervous system depressants, tranquilizers for alleviation of anxiety [1], anti-malarial agent-mefloquine [2], for heat transfer printing of polyester textiles [3], insecticides [4], a developer (blue) for use in sensitive diazo process [5], mutagenic activity [6], intermediate for dyes, germicides, pharmaceuticals, crop protectants [7], intermediates for dye and colourant manufacture [8], pesticides and drug intermediates [9], fungicide [10] and for colour filters [11]. Vibrational spectra of mono-substituted trifluoromethyl benzene (benzotrifluoride-C6 H5 CF3 ) derivatives have been widely studied [12,13]. The microwave spectrum of benzotrifluoride has been studied in the frequency range from 8 to 40 GHz [14]. Raman and infrared spectra of 3-aminobenzotrifluoride in the liquid phase, and single vibronic level fluorescence spectra, in

∗

Corresponding author. Tel.: +914132221847 E-mail addresses: sundaraganesan [email protected] (N. Sundaraganesan), dominic [email protected] (B.D. Joshua). 1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2006.07.004

a supersonic jet, have been reported by Ribeiro-Claro et al. [15]. They explained the spectra on the basis of approximate description of assignment. Recently vibrational spectral studies of 2-amino-5-chloro and 2-amino-5-bromobenzotrifluorides, have been reported by Sing et al. [16]. They interepreted the vibrational spectra by assuming Cs point group symmetry and assigned various modes of vibrations on the basis of observed bands. Literature survey reveals that to the best of our knowledge, neither the complete Raman and IR spectra nor the quantum mechanical calculations for 3-aminobenzotrifluoride have been reported so far. Therefore, the present investigation was undertaken to study the vibrational spectra of this molecule completely and to identify the various normal modes with greater wavenumber accuracy, Ab initio HF and density functional theory (DFT) calculations have been performed to support our wavenumber assignments. 2. Experimental The compound 3ABTF in the liquid form was purchased from the Sigma–Aldrich Chemical Company (USA) with a stated purity of greater than 98% and it was used as such without further purification. The FT-Raman spectrum of 3ABTF has

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215

Fig. 1. FT-IR spectrun of 3-aminobenzotrifluoride.

been recorded using 1064 nm line of Nd:YAG laser as excitation wavelength in the region 100–3500 cm−1 on a Brucker model IFS 66 V spectrophotometer equipped with FRA 106 FT-Raman module accessory. The FT-IR spectrum of this compound was recorded in the region 400–4000 cm−1 on IFS 66 V spectrophotometer using neat technique. The instrument has a resolution of ∼2–3 cm−1 . Multi-tasking OPUS software on a PC/AT 486 computer was used for processes such as signal averaging, signal enhancement and base line corrections. In the FT-IR model the detector was a pyroelectric device incorporating deuterium triglycine sulphate (DTGS) in a temperature resistant alkali metal halide window. The observed experimental FT-IR and FT-Raman spectra are shown in Figs. 1 and 2. The spectral measurements were carried out in Sophisticated Analytical Instrumentation Facility (SAIF), IIT, Chennai. Theoretical

infrared spectra with their scaled frequencies using scale factors for each mode are shown in Figs. 4 and 5. 3. Computational details The entire calculations were performed at Hartree-Fock (HF) and B3LYP levels on a Pentium IV/1.6 GHz personal computer using Gaussian 03W [17] program package, invoking gradient geometry optimization [18]. Initial geometry generated from standard geometrical parameters was minimized without any constraint in the potential energy surface at Hartree-Fock level, adopting the standard 6-31G(d,p) basis set. This geometry was then re-optimized again at B3LYP level, using basis set 6311G(d,p), for better description of polar bonds of NH2 group and CF3 groups. The optimized structural parameters were used

Fig. 2. FT-Raman spectrum of 3-aminobenzotrifluoride.

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in the vibrational frequency calculations at the HF and DFT levels to characterize all stationary points as minima. Then vibrationally averaged nuclear positions of 3ABTF were used for harmonic vibrational frequency calculations resulting in IR and Raman frequencies together with intensities and Raman depolarization ratios. We have utilised the gradient corrected density functional theory (DFT) [19] with the three-parameter hybrid functional (B3) [20] for the exchange part and the Lee-YangParr (LYP) correlation function [21], accepted as a cost-effective approach, for the computation of molecular structure, vibrational frequencies and energies of optimized structures. Vibrational frequencies computed at DFT level have been adjudicated to be more reliable than those obtained by the computation-

ally demanding Moller-Plesset perturbation methods. Density functional theory offers electron correlation frequently comparable to second-order Moller-Plesset theory (MP2). Finally, the calculated normal mode vibrational frequencies provide thermodynamic properties also through the principle of statistical mechanics. By combining the results of the GAUSSVIEW program [22] with symmetry considerations, vibrational frequency assignments were made with a high degree of accuracy. There is always some ambiguity in defining internal coordination. However, the defined coordinate form complete set and matches quite well with the motions observed using the GAUSSVIEW program.

Table 1 Experimental FT-IR and FT-Raman frequencies and assignments for 3-aminobenzotrifluoride (cm−1 ) Species

FT-IR frequency and intensity

A

3484 w

A

A A A

A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A

FT-Raman frequency and intensity 3396 w

3225 w 3059 w 3031 vw 2923 vw 2675 vw 1938 vw 1627 s 1598 w 1530 w 1497 s 1468 vs 1423 w 1341 s 1258 s 1161 w 1123 s 1067 w

3100 w 3065 w 3036 vw

1622 w

1340 ms 1258 w 1173 w 1121 w 1059 w

1000 w 997 ms 897 ms 870 w 789 vs 746 w 698 s 660 ms 617 w 590 w

993 vs 899 w

755 w 750 vs 657 w

538 w 521 w 453 w 437 vw

s: strong; m: medium; vs: very strong; w: week; vw: very week.

438 w 358 w 324 ms 250 w 227 w 180 vw 137 vs

Vibrational assignments NH2 asymmetric stretch NH2 symmetric stretch (1938 + 1258) C–H stretch C–H stretch C–H stretch (1598 + 1314) (1258 + 1423) (1067 + 870) NH2 scissoring C C stretch C C stretch C–C stretch C–C stretch C–C stretch C–CF3 stretch C–NH2 stretch C–H ipb CF3 asymmetric stretch CF3 asymmetric stretch NH2 twisting C–H ipb C–H ipb CCC ipb Ring breathing C–H opb C–H opb C–H opb CF3 symmetric stretch CCC ipb CCC ipb CCC opb CCC opb CF3 asymmetric deform NH2 wagging CCC opb C–NH2 ipb NH2 torsion CF3 symmetric deform CF3 rock C–NH2 opb C–CF3 ipb C–CF3 opb

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4. Results and discussion 4.1. Molecular geometry

Table 2 ˚ Geometrical parameters optimized in 3-aminobenzotrifluoride, Bond length (A), angle (◦ ) and dihedral angle (◦ ) Parameters

The optimized structure parameters of 3ABTF calculated by ab initio HF and DFT B3LYP levels with the 6-31G(d,p) and 6-311G(d,p) basis sets are listed in Table 1 in accordance with the atom numbering scheme given in Fig. 3. Since the crystal structure of the title compound is not available till now, the optimized structure can only be compared with other similar systems for which the crystal structures have been solved. For example, the optimized bond lengths of C–C in phenyl ring ˚ for HF/6-311G(d,p) fall in the range from 1.381 to 1.394 A ˚ and 1.392–1.405 A for B3LYP/6-311G(d,p) methods which are in good agreement with those in experimental bond length ˚ [23]. The optimized of p-methylaniline [1.393(3)–1.401(2) A] ˚ which is C–CF3 bond lengths by two methods are all 1.504 A, ˚ slightly longer than that found in the similar compound [1.481 A] [24]. For the bond of C–F, the optimized lenghts (see Table 2) are also slightly longer than in 2-amino-5-chlorobenzotrifluoride, ˚ [24]. Based on above comparison, although there are 1.350 A some difference between the theoretical values and experimental values, the optimized structural parameters can well reproduce the experimental ones and they are the bases for thereafter discussion. 4.2. Vibrational assignments It has been reported that the substitution of a fluorine atom in the methyl group of toluene [16] reduces the overall symmetry of the molecule. In order to interpret the vibrational spectra of

Fig. 3. Numbering system adopted in this study (3-aminobenzotrifluoride).

217

HF

B3LYP

6-31G(d,p) ˚ Bond lengths (A) C1–C2 C1–C6 C1–C11 C2–C3 C2–H7 C3–C4 C3–N15 C4–C5 C4–H8 C5–C6 C5–H9 C6–H10 C11–F12 C11–F13 C11–F14 N15–H16 N15–H17 Bond angles (◦ ) C2–C1–C6 C2–C1–C11 C6–C1–C11 C1–C2–C3 C1–C2–H7 C3–C2–H7 C2–C3–C4 C2–C3–N15 C4–C3–N15 C3–C4–C5 C3–C4–H8 C5–C4–H8 C4–C5–C6 C4–C5–H9 C6–C5–H9 C1–C6–C5 C1–C6–H10 C5–C6–H10 C1–C11–F12 C1–C11–F13 C1–C11–F14 F12–C11–F13 F12–C11–F14 F13–C11–F14 C3–N15–H16 C3–N15–H17 H16–N15–N17

1.385 1.383 1.504 1.390 1.075 1.395 1.390 1.380 1.076 1.386 1.076 1.073 1.325 1.323 1.326 0.995 0.995

6-311G(d,p) 1.385 1.381 1.504 1.388 1.075 1.394 1.392 1.379 1.076 1.387 1.075 1.072 1.322 1.318 1.321 0.995 0.995

6-31G(d,p) 1.394 1.397 1.505 1.404 1.086 1.407 1.393 1.391 1.087 1.395 1.086 1.083 1.353 1.352 1.356 1.010 1.010

6-311G(d,p) 1.392 1.394 1.504 1.402 1.084 1.405 1.391 1.389 1.085 1.393 1.084 1.081 1.353 1.351 1.356 1.009 1.009

121.2 118.6 120.2 120.2 120.0 119.8 118.6 120.7 120.7 120.5 119.5 120.0 121.0 119.4 119.7 118.4 120.8 120.8 111.9 112.2 111.6 107.3 106.6 106.9 115.1 115.2 111.8

121.2 118.4 120.3 120.3 119.9 119.8 118.6 120.7 120.6 120.5 119.5 120.0 121.0 119.4 119.6 118.4 120.8 120.8 111.6 112.3 111.9 106.9 106.6 107.2 114.7 114.8 111.4

121.1 119.1 119.7 120.3 119.8 119.9 118.5 120.6 120.8 120.6 119.4 120.0 120.9 119.3 119.7 118.6 120.3 121.1 112.1 112.0 111.7 107.4 106.6 106.8 115.5 115.6 112.2

121.2 119.1 119.7 120.3 119.8 119.9 118.4 120.6 120.9 120.6 119.4 120.0 121.0 119.3 119.7 118.5 120.4 121.1 112.3 112.3 111.7 107.1 106.4 106.6 115.8 115.9 112.6

Dihedral angles (◦ ) C6–C1–C2–C3 0.1 C6–C1–C2–H7 −179.2 C11–C1–C2–C3 −177.6 C11–C1–C2–H7 3.1 C2–C1–C6–C5 0.1 C2–C1–C6–H10 179.7 C11–C1–C6–C5 177.7 C11–C1–C6–H10 −2.6 C2–C1–C11–F12 −38.9 C2–C1–C11–F13 −159.6 C2–C1–C11–F14 80.5 C6–C1–C11–F12 143.4 C6–C1–C11–F13 22.7

0.1 179.9 178.2 −2.0 0.0 −179.7 −178.0 2.3 −77.7 162.3 41.7 100.4 −19.7

0.1 −179.2 −177.0 3.8 0.0 179.6 177.0 −3.5 −32.7 −153.4 86.9 150.3 29.5

0.1 −179.1 −177.1 3.7 0.0 179.5 177.2 −3.3 −32.7 −153.5 86.8 150.0 29.2

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Table 2 (Continued ) Parameters

C6–C1–C11–F14 C1–C2–C3–C4 C1–C2–C3–N15 H7–C2–C3–C4 H7–C2–C3–N15 C2–C3–C4–C5 C2–C3–C4–H8 N15–C3–C4–C5 N15–C3–C4–H8 C2–C3–N15–H16 C2–C3–N15–H17 C4–C3–N15–H16 C4–C3–N15–H17 C3–C4–C5–C6 C3–C4–C5–H9 H8–C4–C5–C6 H8–C4–C5–H9 C4–C5–C6–C1 C4–C5–C6–H10 H9–C5–C6–C1 H9–C5–C6–H10

HF

B3LYP

6-31G(d,p)

6-311G(d,p)

6-31G(d,p)

6-311G(d,p)

−97.2 −0.2 −177.6 179.1 1.7 0.2 −179.3 177.6 −1.9 −157.0 −24.6 25.7 158.0 0.0 −179.9 179.5 −0.4 −0.1 −179.8 179.8 0.1

−140.3 −0.2 −177.8 180.0 2.5 0.2 −179.6 177.8 −2.1 −155.7 −24.6 26.8 157.9 −0.1 179.8 179.7 −0.4 0.0 179.7 −179.9 −0.2

−90.2 0.0 −177.1 179.2 2.1 −0.1 −179.6 177.0 −2.5 −158.3 −24.4 24.6 158.6 0.1 −179.8 179.7 −0.3 −0.1 −179.7 179.9 0.3

−90.5 −0.1 −177.1 179.1 2.2 0.0 −179.5 176.9 −2.6 −159.2 −24.0 24.0 159.1 0.1 −179.8 179.7 −0.3 −0.1 −179.6 179.8 0.3

3ABTF it is assumed in which all the atoms of the molecule is in the plane of the phenyl ring, excepting the two F atoms of the CF3 group, which are positioned symmetrically above and below the phenyl ring plane. In accordance with above, the present molecule 3ABTF has Cs point group symmetry. The molecule has 17 atoms and 45 normal modes of fundamental vibrations, which span the irreduciable representations 31A + 14A . All the 45 fundamental vibrations are active in both IR and Raman. The assignments shown in Table 2 for several of phenyl ring modes along with substitutions are briefly given in the present work.

Fig. 4. Comparison of corrected frequencies in cm−1 normalised IR intensities at each level of calculations considered.

4.3. Vibrational frequencies The experimental IR spectra and the stimulated infrared spectra are shown in Figs. 4 and 5, where the calculated intensity is plotted against the harmonic vibrational frequencies. Vibrational frequencies calculated at B3LYP/6-311G(d,p), B3LYP/631G(d,p) levels were scaled by 0.96 [25], and those calculated at HF/6-311G(d,p), HF/6-31G(d,p) levels were scaled by 0.89 [26]. The descriptions concerning the assignment have also been indicated in Table 6. GAUSSVIEW program [22] was used to assign the calculated harmonic frequencies. Comparing the B3LYP and HF methods, above 3000 cm−1 , the predicted frequencies by B3LYP are larger than those by HF; where as under 3000 cm−1 , most of calculated frequencies by HF are larger than those by B3LYP. The harmonic-vibrational frequencies calculated for 3ABTF at HF and B3LYP levels using the triple split valence basis set along with diffused and polarization functions, 6-31G(d,p) and 6-311G(d,p) have been collected in Tables 3–6. The observed FT-IR and FT-Raman frequencies for various modes of vibra-

Fig. 5. Comparison of corrected frequencies in cm−1 normalised IR intensities at each level of calculations considered.

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Table 3 Vibrational wavenumbers obtained for 3-aminobenzotrifluoride at HF/6-31G (d,p) [harmonic frequency (cm−1 ), IR intensities (Km mol−1 ), Raman scattering activities ˚ −1 )] ˚ 4 amu−1 ), Raman depolarization ratio and reduced masses (amu), force constants (m dyne A (A Number

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

Wavenumber

IR intensity

Raman intensity

Unscaled

Scaled

Rel

Abs

Rel

Abs

10 139 188 247 266 344 360 384 475 504 570 579 636 645 720 728 782 820 894 980 989 1009 1083 1106 1156 1182 1216 1268 1333 1347 1382 1386 1466 1492 1629 1674 1795 1809 1826 3340 3362 3363 3396 3810 3918

9 124 167 220 237 306 320 342 423 449 507 515 566 574 641 648 696 730 796 872 880 898 964 984 1029 1052 1082 1129 1186 1199 1230 1234 1305 1328 1450 1490 1598 1610 1625 2973 2992 2993 3022 3391 3487

0 1 0 5 22 4 1 1 1 12 52 1 1 280 12 46 23 9 58 30 34 1 5 1 8 54 18 20 134 317 36 135 16 381 89 19 13 25 135 12 20 5 4 26 20

0 0 0 1 6 1 0 0 0 3 14 0 0 73 3 12 6 2 15 8 9 0 1 0 2 14 5 5 35 83 9 35 4 100 23 5 3 7 35 3 5 1 1 7 5

3 6 0 2 1 3 1 1 0 0 1 5 0 6 3 2 0 11 1 2 2 1 28 0 1 2 2 6 1 2 3 1 0 13 1 0 9 6 33 67 11 173 107 131 58

2 3 0 1 1 2 1 1 0 0 1 3 0 3 2 1 0 6 1 1 1 1 16 0 1 1 1 3 1 1 2 1 0 8 1 0 5 3 19 39 6 100 62 76 34

tions are presented in Table 1. Comparison of the frequencies calculated at HF and B3LYP with experimental values (Table 1) reveals the over estimation of the calculated vibrational modes due to neglect of anharmonicity in real system. Inclusion of electron correlation in density functional theory to a certain extend makes the frequency values smaller in comparison with the HF frequency data. Reduction in the computed harmonic vibrations, though basis set sensitive are only marginal as observed in the DFT values using 6311G(d,p). The reduced mass and force constants along with the depolarization ratios of calculated frequencies have been

Depolarization ratios

Red mass

Force constants

0.75 0.75 0.70 0.73 0.75 0.35 0.61 0.33 0.66 0.62 0.74 0.49 0.48 0.70 0.37 0.74 0.40 0.08 0.75 0.39 0.60 0.74 0.09 0.75 0.48 0.38 0.57 0.75 0.38 0.72 0.17 0.74 0.37 0.10 0.46 0.74 0.59 0.49 0.61 0.60 0.44 0.26 0.19 0.14 0.75

8.4 6.3 7.0 3.5 1.1 7.8 6.1 6.4 4.4 3.3 5.7 6.7 10.6 1.6 6.6 4.3 2.2 9.6 1.5 3.0 2.0 1.4 6.1 1.3 1.9 2.4 1.7 1.4 2.0 12.7 3.4 3.9 1.4 5.1 3.1 2.7 3.3 2.0 2.3 1.1 1.1 1.1 1.1 1.0 1.1

0.00 0.07 0.15 0.12 0.04 0.54 0.47 0.56 0.58 0.49 1.09 1.33 2.54 0.38 2.01 1.34 0.79 3.79 0.71 1.68 1.13 0.84 4.23 0.96 1.53 2.00 1.46 1.30 2.08 13.58 3.77 4.38 1.71 6.71 4.86 4.39 6.30 3.92 4.51 7.16 7.28 7.29 7.44 8.97 9.94

also included in Tables 3–6 to have rational basis for the assignments. 4.4. C–H vibrations The hetero aromatic structure shows the presence of C–H stretching vibrations in the region 3100–3000 cm−1 which is the characteristic region for ready identification of C–H stretching vibrations [27]. In this region, the bands are not affected appreciably by the nature of the substituents. Hence, the FT-IR and FT-Raman bands at 3059, 3031 and 3100, 3065,

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Table 4 Vibrational wavenumbers obtained for 3-aminobenzotrifluoride at HF/6-311G (d,p) [harmonic frequency (cm−1 ), IR intensities (Km mol−1 ), Raman scattering ˚ −1 )] ˚ 4 amu−1 ), Raman depolarization ratio and reduced masses (amu), force constants (m dyne A activities (A Number

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

Wavenumber

IR intensity

Raman intensity

Unscaled

Scaled

Rel

Abs

Rel

Abs

9 139 188 245 259 345 361 382 476 505 575 578 639 661 722 731 778 823 889 972 984 1005 1078 1099 1147 1175 1207 1262 1319 1323 1367 1371 1458 1481 1617 1662 1783 1799 1816 3319 3339 3342 3376 3787 3885

8 124 167 218 230 307 322 340 424 449 511 514 568 588 643 651 692 732 791 865 876 894 959 978 1021 1045 1074 1123 1174 1177 1216 1220 1297 1318 1439 1479 1587 1601 1617 2954 2972 2974 3004 3371 3457

0 1 1 6 21 5 0 1 1 12 37 5 1 231 9 74 34 9 59 28 35 2 5 0 7 65 25 23 171 331 90 73 15 405 91 18 25 4 144 11 10 13 3 26 18

0 0 0 1 5 1 0 0 0 3 9 1 0 57 2 18 8 2 14 7 9 0 1 0 2 16 6 6 42 82 22 18 4 100 23 5 6 1 36 3 3 3 1 6 4

3 5 0 2 0 3 1 1 0 0 1 1 0 5 3 2 0 11 0 2 1 0 31 0 0 2 2 5 1 2 2 3 0 13 1 0 11 7 28 68 26 161 106 135 54

2 4 0 1 0 2 0 1 0 0 1 1 0 4 3 1 0 8 0 2 1 0 23 0 0 1 1 4 1 1 2 2 0 10 1 0 8 5 21 50 19 119 79 100 40

3036 cm−1 , respectively in 3ABTF have been designated to C–H stretching vibrations. The scaled vibrations at 3083, 3054, 3053 and 3032 cm−1 (mode nos. 43 and 40) corresponds to stretching mode of CH unit. The C–H in-plane bending vibrations assigned at 1042–1286 cm−1 (mode nos. 26, 28, 30–32) even though found to be contaminated by –NH2 twisting and C–CF3 stretching are in the range found in literature [28,29], while the experimental observations are at 1000–1173 cm−1 . The calculated frequencies 764–937 cm−1 for the C–H outof-plane bending falls in the FT-IR/FT-Raman values of 755–870 cm−1 .

Depolarization ratios

Red mass

Force constants

0.75 0.75 0.69 0.72 0.75 0.35 0.53 0.33 0.70 0.50 0.56 0.45 0.45 0.61 0.48 0.66 0.62 0.06 0.43 0.22 0.44 0.17 0.09 0.70 0.54 0.26 0.42 0.74 0.35 0.75 0.25 0.16 0.32 0.10 0.35 0.71 0.54 0.54 0.56 0.61 0.38 0.28 0.22 0.14 0.75

8.4 6.3 7.0 3.5 1.1 7.3 6.5 6.1 4.4 3.2 6.4 6.6 11.1 1.6 7.4 3.2 2.3 9.6 1.5 2.5 2.3 1.4 6.1 1.3 2.1 2.4 1.8 1.3 2.1 11.0 5.1 2.5 1.3 5.1 3.0 2.6 4.2 2.6 1.6 1.1 1.1 1.1 1.1 1.0 1.1

0.00 0.07 0.15 0.12 0.04 0.51 0.50 0.53 0.59 0.48 1.24 1.31 2.66 0.42 2.26 1.00 0.81 3.84 0.70 1.41 1.29 0.83 4.17 0.94 1.63 1.99 1.50 1.26 2.12 11.31 5.63 2.72 1.69 6.56 4.69 4.29 7.87 4.98 3.19 7.07 7.18 7.20 7.35 8.86 9.77

4.5. C–NH2 vibrations The molecule under investigation possesses only one NH2 group and hence one expects one symmetric and one asymmetric N–H stretching vibrations in NH2 group. In all the primary aromatic amines the N–H stretching frequency occurs in the region 3300–3500 cm−1 [30]. Hence the bands at 3484 and 3396 cm−1 are assigned to N–H asymmetric and symmetric stretching vibrations, respectively in NH2 group. These observations agree well with the earlier reports [31]. The scaled –NH2 asymmetric and symmetric stretching in the range 3524–3429 cm−1 (mode nos.

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Table 5 Vibrational wavenumbers obtained for 3-aminobenzotrifluoride at B3LYP/6-31G (d,p) [harmonic frequency (cm−1 ), IR intensities (Km mol−1 ), Raman scattering ˚ −1 )] ˚ 4 amu−1 ), Raman depolarization ratio and reduced masses (amu), force constants (m dyne A activities (A Number

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

Wavenumber

IR intensity

Raman intensity

Unscaled

Scaled

Rel

Abs

Rel

Abs

23 128 175 225 314 318 330 358 436 459 516 537 564 580 655 667 711 752 799 876 891 918 973 1010 1085 1095 1145 1182 1199 1212 1285 1344 1365 1378 1508 1544 1648 1662 1680 3176 3198 3200 3230 3578 3685

22 123 168 216 301 305 317 344 419 441 495 516 542 557 629 640 683 722 767 841 856 881 934 970 1041 1051 1099 1134 1151 1164 1233 1290 1311 1323 1448 1482 1582 1596 1613 3049 3070 3072 3101 3435 3538

0 1 0 4 7 13 1 1 1 10 71 25 253 2 12 14 11 4 41 21 2 30 0 6 23 44 4 256 6 191 117 36 255 12 64 20 9 10 144 11 18 3 3 21 14

0 0 0 2 3 5 0 0 0 4 28 10 99 1 5 6 4 1 16 8 1 12 0 2 9 17 2 100 3 75 46 14 100 5 25 8 3 4 56 4 7 1 1 8 5

4 6 0 1 2 2 1 1 0 0 2 4 7 1 1 2 0 13 3 2 2 3 1 27 0 3 6 3 5 0 1 3 17 3 2 1 6 6 34 74 59 133 113 177 67

2 4 0 1 1 1 1 1 0 0 1 2 4 1 0 1 0 7 2 1 1 2 0 15 0 2 3 2 3 0 1 2 10 2 1 1 3 3 19 42 33 75 64 100 38

45 and 44). Bellamy and Mancy [30,32] suggested that the NH2 scissoring modes lie in the region 1590–1650 cm−1 . In accordance with their conclusion, the NH2 scissoring mode is identified with strong band at 1627 cm−1 in FT-IR and weak band at 1622 cm−1 in FT-Raman, respectively in the present work. The computed –NH2 scissoring vibration at 1603 cm−1 is in excellent agreement with the recorded spectral data. The FT-IR and FT-Raman stretching mode both at 1258 cm−1 corresponding to C–NH2 moiety was calculated to be1298 cm−1 (mode no. 33). The C–NH2 out-of-plane and in-plane bend-

Depolarization ratios

Red mass

Force constants

0.75 0.75 0.72 0.71 0.54 0.39 0.53 0.36 0.65 0.74 0.74 0.45 0.70 0.50 0.24 0.70 0.62 0.07 0.75 0.71 0.72 0.33 0.75 0.09 0.50 0.31 0.73 0.54 0.73 0.75 0.48 0.13 0.12 0.23 0.67 0.58 0.50 0.48 0.61 0.54 0.28 0.27 0.19 0.15 0.75

8.5 6.5 6.9 3.6 1.6 2.2 6.7 7.0 4.2 3.5 4.2 6.3 1.6 9.5 4.9 8.7 2.3 9.5 1.5 1.5 1.4 4.7 1.3 6.1 1.7 2.2 1.3 10.3 1.1 7.0 2.6 1.5 4.2 6.0 3.3 2.7 5.0 1.7 2.5 1.1 1.1 1.1 1.1 1.0 1.1

0.00 0.06 0.12 0.11 0.09 0.13 0.43 0.53 0.48 0.43 0.66 1.08 0.30 1.88 1.23 2.27 0.70 3.15 0.57 0.69 0.64 2.35 0.71 3.69 1.21 1.59 1.00 8.46 0.97 6.09 2.55 1.57 4.64 6.66 4.45 3.79 8.02 2.70 4.16 6.47 6.58 6.58 6.72 7.90 8.80

ing vibrations at 212 and 343 cm−1 , respectively, are also in good agreement with the assignment in the experimental data. The NH2 wagging computed at 533 cm−1 (mode no. 13) shows excellent agreement with FT-IR experimental data at 521 cm−1 . The NH2 twisting vibration calculated to be 1035 cm−1 (mode no. 25) is also in very good agreement with recorded value of 1067 cm−1 in FT-IR spectra. It should be emphasized that the wavenumber calculated by B3LYP/6-311G(d,p) method for torsion mode at 298 cm−1 (mode no. 5) is deviating negatively by ∼60 cm−1 from FT-Raman spectra.

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Table 6 Vibrational wavenumbers obtained for 3-aminobenzotrifluoride at B3LYP/6-311G (d,p) [harmonic frequency (cm−1 ), IR intensities (Km mol−1 ), Raman scattering ˚ −1 )] ˚ 4 amu−1 ), Raman depolarization ratio and reduced masses (amu), force constants (m dyne A activities (A Number

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

Wavenumber

IR intensity

Raman intensity

Unscaled

Scaled

Rel

Abs

Rel

Abs

18 127 175 221 311 317 330 358 437 459 517 537 555 580 653 669 708 750 796 875 892 912 976 1010 1078 1086 1135 1140 1172 1195 1273 1340 1352 1361 1497 1532 1634 1653 1670 3159 3180 3182 3212 3571 3670

17 122 168 212 298 304 317 343 420 441 496 516 533 557 627 642 680 720 764 840 856 875 937 969 1035 1042 1089 1095 1126 1147 1222 1286 1298 1306 1437 1471 1569 1587 1603 3032 3053 3054 3083 3429 3524

0 1 1 4 13 5 1 1 1 14 99 43 193 1 5 12 21 3 46 24 2 37 0 8 32 60 275 15 191 6 145 57 196 49 65 21 13 7 156 11 15 4 2 25 15

0 0 0 2 5 2 0 0 0 5 36 16 70 0 2 5 8 1 17 9 1 14 0 3 12 22 100 5 70 2 53 21 71 18 24 8 5 2 57 4 5 1 1 9 6

3 6 0 1 1 3 1 2 0 0 2 3 6 1 1 2 0 13 1 1 0 4 0 29 0 3 2 5 1 2 1 5 13 6 2 1 6 9 28 80 17 187 119 188 65

2 3 0 1 0 1 1 1 0 0 1 2 3 1 0 1 0 7 0 0 0 2 0 15 0 2 1 3 0 1 1 3 7 3 1 1 3 5 15 42 9 99 63 100 35

Depolarization ratios

Red mass

Force constants

Vibrational assignments

0.75 0.75 0.72 0.71 0.66 0.37 0.50 0.35 0.63 0.62 0.70 0.46 0.58 0.48 0.25 0.67 0.36 0.06 0.75 0.69 0.38 0.23 0.74 0.09 0.68 0.24 0.54 0.71 0.65 0.74 0.52 0.13 0.15 0.15 0.62 0.61 0.41 0.74 0.56 0.55 0.36 0.29 0.21 0.16 0.75

8.5 6.4 6.9 3.6 1.1 5.6 6.4 6.9 4.2 3.3 3.5 5.5 1.8 9.8 4.8 8.7 2.2 9.8 1.6 1.6 1.4 4.9 1.3 6.1 1.8 2.3 10.5 1.4 6.0 1.1 2.7 1.6 4.2 4.2 3.3 2.6 5.6 2.4 1.6 1.1 1.1 1.1 1.1 1.0 1.1

0.00 0.06 0.12 0.10 0.06 0.33 0.41 0.52 0.48 0.41 0.55 0.93 0.33 1.94 1.20 2.30 0.66 3.27 0.58 0.70 0.65 2.39 0.72 3.69 1.26 1.62 7.94 1.04 4.87 0.94 2.58 1.68 4.56 4.56 4.31 3.66 8.84 3.88 2.66 6.39 6.50 6.51 6.65 7.87 8.73

τ CF3 γ C–CF3 β C–CF3 γ C–NH2 + γ CCC τ NH2 β CCC β C–NH2 β C–NH2 + δs CF3 β C–NH2 γ CCC γ CCC + ω NH2 β C–NH2 ω NH2 δas CF3 γ CCC β CCC γ CH νs CF3 + β CCC γ CH γ CH γ CH Ring breathing γ CH Ring deform t NH2 + β CH β CH + ν CC νas CF3 β CH + t NH2 ν C–F in CF3 β CH ν C–CF3 + β CH β CH ν C–NH2 + ν CC ν CC ν CC ν CC ν CC NH2 scissoring + ν CC NH2 scissoring ν CH ν CH ν CH ν CH νs NH2 νas NH2

ν: stretching; νs : symmetric stretching; νas : asymmetric stretching; β: in-plane-bending; γ: out-of-plane bending; δa : symmetric deform; δas : asymmetric deform; ω: wagging; ρ: rocking; t: twisting; τ: torsion.

4.6. C–C vibrations

4.7. C–CF3 vibrations

The C–C aromatic stretch, known as semicircle stretching, predicted at 1569 cm−1 (mode no. 37) is in excellent agreement with experimental observation of Raman value at 1598 cm−1 . The ring breathing mode at 912 cm−1 (unscaled, mode no. 22) coincides satisfactorily with recorded value of 897/899 cm−1 in FT-IR/FT-Raman spectra [33]. The theoretically calculated C–C–C out-of-plane and in-plane bending modes have been found to be consistent with the recorded spectral values.

The C–CF3 streching mode has been assigned in the range 1300–1360 cm−1 in benzene derivatives containing a CF3 group [12–13,34–36]. In the present case, strong FT-IR band at 1341 cm−1 with medium Raman lines at 1340 cm−1 are assigned to the C–CF3 stretching modes for 3ABTF. The theoretically computed unscaled value at 1363 cm−1 (mode no. 31) by HF/6311G(d,p) shows excellent agreement with recorded experimental data when compared with unscaled value at 1273 cm−1 (mode

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no. 31) by DFT/6-311G(d,p). Force field calculations placed the in-plane and out-of-plane C-CF3 bending modes at ∼130 and 100 cm−1 [12,36–38]. In the present study, the ␤(C–CF3 ) mode is assigned at 180 cm−1 . The ␥(C–CF3 ) bending mode is observed at 137 cm−1 . The theoretically computed value at 168 and 122 cm−1 (mode nos. 3 and 2) by B3LYP/6-311G(d,p) method shows excellent agreement with our experimental observations for in-plane and out-of-plane bending modes of C–CF3 , respectively. 4.8. CF3 group vibrations The symmetric stretching for the NH2 , CH3 , CH2 , CF2 and CCl2 has magnitude lower than the anti-symmetric stretching. For the CF3 group compounds some workers have assigned the symmetric stretching mode at a higher magnitude (∼1325 cm−1 ) than the anti-symmetric stretching mode (1100–1200 cm−1 ). Whereas some other workers have assigned the symmetric stretching mode at a lower magnitude (∼725–785 cm−1 ) than its anti-symmetric stretching counterpart (1100–1200 cm−1 ). In 2-amino-5-chloro and 2-amino-5-bromobenzotrifluorides [37] the symmetric CF3 stretching mode νs (CF3 ) appears at a lower magnitude, in the range 700–800 cm−1 , compared to its antisymmetric stretching νas (CF3 ) which appear in the range 1100–1200 cm−1 . Moreover, the νs mode is observed as a strong FT-Raman band and the νas modes are observed as strong FTIR bands [12,13,36–38]. In the present study, the strongest FT-Raman frequencies at 750 cm−1 and weak FT-IR band at 746 cm−1 are assigned to νs (CF3 ) mode for 3ABTF. Usually, the two compounds of the CF3 asymmetric stretching mode are observed to have nearly same magnitude [12]. The CF3 asymmetric stretching modes are observed at 1161 cm−1 in FT-IR and 1123/1121 cm−1 (FT-IR/FT-Raman) are assigned to CF3 asymmetric stretching modes. The theoretically computed value at 720 and 1089 cm−1 (mode nos. 18 and 27) could be well correlated with experimental observations for νs (CF3 ) and νas (CF3 ) modes, respectively. Assignments for the symmetric and antisymmetric deformation modes and the rocking modes of the CF3 group are assigned in the region 200–600 cm−1 [12–13,36–38]. A FT-Raman fre-

223

quency with moderate to strong intensity is observed in the spectra of CF3 containing benzene derivatives in the region 300–400 cm−1 which appears to be characteristic frequencies of the CF3 group. This frequency is correlated to the δs (CF3 ) mode (A ) by a number of workers [12–13,36–38]. For 5-amino-2fluorobenzotrifluorides and 5-amino-2-chlorobenzotrifluorides, the frequencies 330 and 305 cm−1 with appreciable intensity and polarised were assigned to the symmetric CF3 deformation mode. In the present study a medium strong band at 324 cm−1 in FT-Raman spectrum is assigned to CF3 symmetric deformation. The calculated frequency at 343 cm−1 (mode no. 8) coincides well with experimental observations. Assignments of the two CF3 asymmetric deformation modes have been proposed in the wavenumber region 490–600 cm−1 [24]. However, in the assignment of the CF3 asymmetric deformation mode, there is controversy amongst different group of workers [12–13,24]. In our study only one band is observed at 538 cm−1 in FT-Raman is attributed to CF3 asymmetric deformational mode. The theoretically predicted value also shows one frequency at 557 cm−1 (mode no. 14) which is in excellent agreement with recorded spectral data. However, the rocking modes of CF3 appear to have variable magnitudes in CF3 containing benzene. The CF3 rocking mode is observed at 250 cm−1 in FT-Raman spectra. However the calculated results shows that no such frequency exists for rocking modes of CF3 group. The mode with the lowest magnitude is the torsion mode of CF3 group and it lies beyond the investigated region. The theoretically calculated value by B3LYP/6-311G(d,p) corresponding to this mode is at 17 cm−1 (mode no. 1) for 3ABTF. The force constant values computed at HF and DFT level of theories at various basis set have been collected in Tables 3–6. These force constant value on comparison with related molecule [24] are found to deviate approximately by one unit. 5. Other molecular properties Several calculated thermodynamic parameters are presented in Table 7. Scale factors have been recommended [39] for an accurate prediction in determining the zero-point vibration energies (ZPVE), and the entropy, Svib (T). The variations in the

Table 7 Theoretically computed energies (a.u.), zero-point vibrational energies (kcal mol−1 ), rotational constants (GHz), entropies (cal mol−1 K−1 ) and dipole moment (D) for 3-aminobenzotrifluoride Parameters

Total energy Zero-point energy Rotational constants Entropy Total Translational Rotational Vibrational Dipole moment

HF

B3LYP

6-31G(d,p)

6-311G(d,p)

6-31G(d,p)

6-311G(d,p)

−621.3685367 82.35 2.1489 0.7530 0.6162

−621.5112596 81.88 2.1535 0.7543 0.6171

−624.6529742 76.64 2.0996 0.7405 0.6065

−624.8224829 76.16 2.1051 0.7414 0.6074

96.061 41.138 30.157 24.766 3.653

96.390 41.138 30.151 25.100 3.848

96.332 41.138 30.212 24.982 3.660

96.953 41.138 30.207 25.607 3.962

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ZPVEs seem to be insignificant. The total energies are found to decrease with the increase of the basis set dimension. The changes in the total entropy of 3ABTF at room temperature at different basis set are only marginal. 6. Conclusion Attempts have been made in the present work for the proper frequency assignments for the compound 3ABTF from the FTIR and FT-Raman spectra. The equilibrium geometries and harmonic frequencies of 3ABTF were determined and analysed both at HF and DFT level of theories utilizing 6-31G(d,p) and 6311G(d,p) basis sets, giving allowance for the lone pairs through diffused functions. The difference between the observed and scaled wave number values of most of the fundamentals is very small. Any discrepancy noted between the observed and the calculated frequencies may be due to the fact that the calculations have been actually done on a single molecules in the gaseous state contrary to the experimental values recorded in the presence of intermolecular interactions. Therefore, the assignments made at higher levels of theory with only resonable deviations from the experimental values, seem to be correct. References [1] L. Henry, E.R. Yale, Squibb and Sons Inc., US 3, 935, 230 (1976); Appl. 71 (1970) 234. [2] Guenther Grethe, Thomas Mitt, F. Haffman-La Roche and Co., Gen. Offen. 2, 806, 909 (1978); Appl. 769 (1977) 816. [3] I. Russel Steiner, Compton and Knowies corp., US 4, 234, 481 (1980); Appl. 847 (1977) 892. [4] Albert J. Clinton, O.K. George O’D’oherty, C. Lilly, Dli and Co., US 4, 316, 988 (1982); Appl. 706 (1976) 23. [5] Richo Co. Ltd. Jpn. Knokai Tokkyo Koho Jp 58, 201, 755 (1983); Appl. 82/81 (1982) 570. [6] A. Buzzati-Traverso, Pavia, (iItaly) Farmaco, Ed, Prat., 215 (1986). [7] Max. M. Boudakian, Olin Corp., US 4, 582, 925 (1986); Appl. 685 (1984) 6. [8] Edward W. Kluger, Patrick D. Moore, Joe T. Burchette, Milliken Research Corp., US 4, 761, 502 (1988); Appl. 904 (1986) 459. [9] Ference Knok, Gyulla Zollner, Lajos Sarosi, Budapesti Vegyimuevek, Teljes Hu 47, 517 (1986); Appl. 87/4 (1987) 42. [10] Miroslav Czech. Veverka (1992); Appl. 88/4 (1988) 496. [11] Naoto Ito, Hiroshi Aiga, Mitsui Toatsu Chemicals, Japan, Jp 8, 100, 127 (1996); Appl. 94/269 (1994) 512. [12] R.A. Yadav, Ph.D., Thesis, Banaras Hindu University, Varanasi, India, 1983.

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