untitled European Journal of Chemistry 2 (1) (2011) 70‐76 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2011 EURJCHEM DOI:10.5155/eurjchem.2.1.70‐76.286 European Journal of Chemistry Journal homepage: www.eurjchem.com Synthesis, FT‐IR, FT‐Raman and quantum chemical investigations of N‐(3‐methylphenyl)‐2,2‐dichloroacetamide Velu Arjunana,*, Thiruvengadam Ranib, Chithathoor Venugopal Mythilic and Sriramulu Mohand a Department of Chemistry, Kanchi Mamunivar Centre for Post‐Graduate Studies, Puducherry, IN‐605008, India b Centre for Research and Development, PRIST University, Thanjavur, IN‐613403, India c Department of Chemistry, Rani Anna Government College for Women, Tirunelveli, IN‐627008, India d Department of Mathematical and Physical Sciences, Hawasa University, Hawasa, Ethiopia *Corresponding author at: Department of Chemistry, Kanchi Mamunivar Centre for Post‐Graduate Studies, Puducherry, IN‐605008, India. Tel.: +91.413.2211111; fax: +91.413.2251613. E‐mail address: varjunftir@yahoo.com (V. Arjunan). ARTICLE INFORMATION ABSTRACT Received: 20 September 2010 Received in revised form: 12 January 2011 Accepted: 26 January 2011 Online: 31 March 2011 KEYWORDS N‐(3‐methylphenyl)‐2,2‐dichloroacetamide of the configuration XyC6H5‐y‐NHCO‐CHCl2 (where, X = CH3 and y =1) was synthesized and an extensive spectroscopic investigations have been carried out by recording the Fourier transform infrared (FT‐IR) and FT‐Raman spectra in an effort to provide the complete analysis of the fundamental modes of the compound. The ab initio and DFT studies were carried out with 6‐311++G(d,p) and 6‐31G(d,p) basis set to determine the structural, thermodynamical and vibrational characteristics of the compound. The steric influence of methyl group on the characteristic frequencies of amide (‐CONH‐) group has been analysed. FT‐IR FT‐Raman N‐(3‐methylphenyl)‐2,2‐dichloroacetamide DFT Ab initio Synthesis 1. Introduction Amides are of fundamental interest since conjugation between nitrogen lone‐pair electrons and the carbonyl ‐bond, results in distinct physical and chemical properties. As a result of conjugation between the carbonyl bond and the nitrogen lone pair, the C‐N bond in amides possesses considerable double bond character thus; one can expect restricted rotation about this bond and a planar configuration for the amide group. This planar structure has been confirmed by measurement with X‐rays and the trans‐ configuration is the most stable and it has been shown that protein chains involve this structure [1‐ 9]. N‐phenylacetamide is an interesting system because the nearly planar amide group display bond distances, which are close to those found in polypeptides. Spectroscopic and crystal structural studies give valuable informations on bond properties. The –CO‐NH‐ group adopts a planar ‘peptide‐like’ conformation, as in the case of formamide [10], methyl hydrazinocarboxylate [11], N‐methylformamide [12], o‐methyl acetanilide [13] and formanilide [14,15]. Many N‐phenylacetamide derivatives exhibit fungicidal, herbicidal and pharmacological activities which further stimulated the recent interest in their chemistry. Anilide herbicides such as alachlor, acetochlor, metolachlor, pretilachlor and butachlor are promising weed control agents for a wide variety of economically important crops including rice, cotton, potatoes and corns [16‐21]. N‐phenylacetamide is used in medicine under the name antifebrin, as a febrifuge and it has pain relieving properties [22]. Acetanilide is a useful intermediate in various reactions of aniline in which it is desirable to protect the amino group. As amides are the simplest model for peptides and also due to the fungicidal, herbicidal and several pharmacological activities of many acetanilide derivatives, their exact structure has been the subject of many experimental and theoretical studies [23‐28]. The vibrational spectroscopic analysis of N‐(3‐ methylphenyl)‐2,2‐dichloroacetamide has not been studied. Thus, in continuation of earlier studies on N‐(chloro substituted phenyl)‐2,2‐dichloroacetamides [1] and N‐(2‐ methylphenyl)‐, and N‐(4‐methylphenyl)‐2,2‐dichloroacet amides [29], the N‐(3‐methylphenyl)‐2,2‐dichloroacetamide (3MPA) of the configuration XyC6H5‐y‐NHCO‐CHCl2 (where, X = CH3 and y = 1) has been synthesised. Spectroscopic and quantum chemical studies were carried out on 3MPA in an effort to provide possible explanations for vibrational frequencies and to understand the effect of methyl group on the characteristic frequencies of amide group. 2. Experimental 2.1. Synthesis The compound N‐(3‐methylphenyl)‐2,2‐dichloroacetamide was synthesized from methylaniline, dichloroacetic acid and phosphorus oxychloride based on the procedure reported [1,29]. The pure samples of 3‐methylaniline, dichloroacetic acid and phosphorus oxychloride were purchased from Aldrich chemicals, USA and are used as such without further purification. All other chemicals used are of analar (AR) grade. The synthesized crude compound was recrystallised from ethanol several times. The yield of the product is about 65%. The melting point of the recrystallised sample is 99 oC. The Arjunan et al. / European Journal of Chemistry 2 (1) (2011) 70‐76 71 purity of the compound was confirmed by chemical analysis for C, H and N. The % found (calculated) C 49.59 (49.57), H 4.15 (4.16) and N 6.39 (6.42). The simple reaction is shown in Scheme 1. Scheme 1 2.2. Instrumentation The FT‐IR spectrum of the compound was recorded by KBr disc method in the range of 4000 to 400 cm‐1 with Shimadzu FTIR‐8400 spectrometer, features a temperature stabilized DLATGS detector, 30 degree Michelson interferometer and a high‐energy ceramic globar source. The spectral resolution is 2 cm‐1. The FT‐Raman spectrum of the compound was recorded in the Bruker IFS 66V spectrometer with FRA 106 Raman module. The Raman spectrum was obtained in the wavenumber range 3500–100 cm‐1. The light scattering was excited using a low‐noise diode pumped Nd:YAG laser source operating at 1.064 m with 200 mW power. A special (enhanced) liquid nitrogen cooled germanium detector was used. The frequencies of all sharp bands are accurate to 2 cm‐1. 2.3. Computational details The gradient corrected density functional theory (DFT) [30] with the three‐parameter hybrid functional Becke3 (B3) [31] for the exchange part and the Lee‐Yang‐Parr (LYP) correlation function [32], level of calculations have been carried out in the present investigation, using 6‐311++G(d,p) basis sets with Gaussian 03 [33] program package. Following geometry optimisations with HF and B3LYP method using 6‐ 311++G(d,p) and 6‐31G(d,p) basis sets to characterise all stationary points as minima, the vibrational frequencies resulting in IR and Raman frequencies together with intensities, Raman depolarization ratios and thermodynamical parameters were determined. Owing to the complexity of the molecule, the potential energy distribution of the vibrational modes of the compounds are also calculated through normal coordinate analysis [34‐36] using the force constants obtained from the B3LYP/6‐311++G(d,p) method utilising the program of Fuhrer et al. [37]. 3. Results and discussion 3.1. Molecular geometry The molecular structure and atom numbering scheme of the compound 3MPA under investigation is shown in Figure 1. The geometry of the molecule is considered by possessing CS point group symmetry. The 60 fundamental vibrations of 3MPA span the irreducible representations 39A + 21A. All the vibrations are active in both IR and Raman. 3.2. Structural properties The optimized structural parameters bond lengths and the bond angles for the thermodynamically preferred geometry of 3MPA at HF and B3LYP levels with 6‐31G(d,p) and 6‐ 311++G(d,p) basis sets are presented in Table 1 in accordance with the atom numbering scheme of the molecules shown in Figure 1. The bond lengths between the amide nitrogen and the aromatic ring, C6‐N7 and between the amide nitrogen and the carbonyl carbon atom, N7‐C8 given in Table 1 reflect the changes in conjugation. The adjacent methyl group influence on the rotation of acylamino group. The steric interaction of methyl substituent on the ring is of great importance in determining its structural and vibrational properties. As the steric hindrance increases and the plane of acylamino group rotates, the C6‐N7 bond becomes longer and the N7‐C8 bond becomes shorter. The thermodynamic parameters of the compound has also been computed at HF and B3LYP methods with 6‐311++G(d,p) basis sets and are presented in Table 2. The calculated SCF energy and entropy of the compounds clearly indicates that 3MPA is more stable than 2MPA [29]. The bond length of the compounds 3MPA determined at the DFT level of theory is in good agreement with the structural parameters of N‐phenylacetamide [38]. C1 C2 C3 C4 C5 C6 C17 N7 C8 H18 C9 O10 H15 H14 H13 H16 H20H21 H22 H19 Cl11 Cl12 Figure 1. Molecular structure and atom numbering of N‐(3‐methylphenyl)‐ 2,2‐dichloroacetamide. 3.3. Vibrational analysis The FT‐IR and FT‐Raman spectra of N‐(3‐methylphenyl)‐ 2,2‐dichloroacetamide are shown in Figures 2 and 3. All the observed wavenumbers are assigned in terms of fundamentals, overtones and combination bands. The observed and calculated frequencies by ab initio and DFT methods along with their relative intensities, probable assignments, depolarization ratios and potential energy distributions (PED) of 3MPA are summarized in Tables 3 and 4. Figure 2. FT‐IR and theoretical spectra of N‐(3‐methylphenyl)‐2,2‐ dichloroacetamide. 72 Arjunan et al. / European Journal of Chemistry 2 (1) (2011) 70‐76 Table 1. Structural parameters calculated for N‐(3‐methylphenyl)‐2,2‐dichloroacetamide employing HF and B3LYP methods with 6–311++G(d,p) and 6–31G(d,p) basis sets. Structural parameters N‐(3‐methylphenyl)‐2,2‐dichloroacetamide HF 6–311++G(d,p) B3LYP 6–311++G(d,p) HF 6–31G(d,p) B3LYP 6–31G(d,p) Experimental b Internuclear distance (Å) C1‐C2 1.384 1.392 1.383 1.393 1.384 C2‐C3 1.384 1.393 1.384 1.395 1.376 C3‐C4 1.388 1.398 1.388 1.400 1.391 C4‐C5 1.387 1.395 1.388 1.398 1.379 C5‐C6 1.389 1.399 1.389 1.401 1.397 C6‐C1 1.389 1.400 1.390 1.402 1.391 C6‐N7 1.413 1.415 1.413 1.415 1.413 N7‐C8 1.346 1.359 1.346 1.360 1.354 C8‐C9 1.537 1.542 1.537 1.544 1.495 C8‐O10 1.189 1.216 1.194 1.221 1.219 C4‐C17 1.511 1.510 1.511 1.511 C9‐Cla 1.778 1.804 1.776 1.806 C‐H (Ring)a 1.075 1.084 1.075 1.085 C17‐H (Methyl)a 1.085 1.093 1.084 1.093 N7‐H18 0.994 1.011 0.994 1.012 C9‐H19 1.072 1.083 1.073 1.086 Bond angle (o) C2‐C1‐C6 118.515 118.573 118.525 118.539 C2‐C1‐H13 120.684 121.207 120.812 121.477 C6‐C1‐H13 120.801 120.220 120.662 119.984 C1‐C2‐C3 121.620 121.392 121.605 121.386 C1‐C2‐H14 118.787 118.908 118.791 118.927 C3‐C2‐H14 119.595 119.701 119.605 119.687 C2‐C3‐C4 120.047 120.382 120.058 120.386 C2‐C3‐H15 119.914 119.959 119.944 120.020 C4‐C3‐H15 120.039 119.659 120.999 119.594 C3‐C4‐C5 118.488 118.319 118.522 118.365 C3‐C4‐C17 121.442 121.383 121.448 121.374 C5‐C4‐C17 120.070 120.298 120.030 120.261 C4‐C5‐C6 121.414 121.357 121.356 121.267 C4‐C5‐H16 119.218 119.322 119.213 119.338 C6‐C5‐H16 119.369 119.321 119.431 119.395 C1‐C6‐C5 119.918 119.977 119.935 120.057 C1‐C6‐N7 123.591 123.198 123.531 123.055 C5‐C6‐N7 116.491 116.825 116.534 116.888 C6‐N7‐H18 114.908 115.086 115.020 115.266 C6‐N7‐C8 128.813 129.006 128.633 128.717 H18‐N7‐C8 116.279 115.908 116.348 116.017 O10‐C8‐N7 126.956 126.867 127.031 127.038 O10‐C8‐C9 117.842 118.222 117.702 118.095 N7‐C8‐C9 115.202 114.911 115.267 114.867 C8‐C9‐Cl11 111.513 111.701 111.571 111.642 C8‐C9‐Cl12 111.510 111.697 111.566 111.639 C8‐C9‐H19 107.290 107.642 106.983 107.460 Cl11‐C9‐Cl12 111.029 110.955 111.098 110.967 Cl11‐C9‐H19 107.635 107.293 107.690 107.443 Cl12‐C9‐H19 107.635 107.292 107.689 107.443 C4‐C17‐H20 111.071 111.190 111.172 111.278 C4‐C17‐H22 110.961 111.243 111.074 111.364 C4‐C17‐H21 110.967 111.250 111.080 111.369 H20‐C17‐H22 107.985 107.890 107.894 107.754 H20‐C17‐H21 107.989 107.826 107.898 107.762 H21‐C17‐H21 107.727 107.332 107.563 107.112 Dihedral angle (o) C2‐C1‐C6‐N7 ‐179.998 ‐180.000 ‐179.999 ‐179.998 C4‐C5‐C6‐N7 180.000 180.000 180.000 180.000 C1‐C6‐N7‐H18 179.998 180.000 179.998 180.000 C1‐C6‐N7‐C8 0.004 0.004 0.005 0.002 C5‐C6‐N7‐H18 0.004 0.003 0.003 0.002 C5‐C6‐N7‐C8 ‐179.994 ‐179.994 ‐179.994 ‐179.997 C6‐N7‐C8‐O10 0.007 0.001 0.002 0.002 C6‐N7‐C8‐C9 ‐180.000 ‐180.000 ‐179.995 ‐179.997 H18‐N7‐C8‐O10 ‐180.000 ‐180.000 ‐179.995 ‐179.996 a Mean value; b values taken from Ref. [38]. 3.3.1. Carbon‐carbon vibrations The C‐C stretching modes of 3MPA are assigned to the bands observed at 1595, 1432, 1410 and 1357 cm‐1 in the Raman spectrum. The C‐C stretching modes of 3MPA is observed in the range 1595‐1357 cm‐1 while in the case of 2MPA and 4MPA these are obtained in the range 1644‐1382 cm‐1 and 1642‐1307 cm‐1, respectively [29]. The vibrational frequencies observed in the Raman spectrum of 3MPA at 1217 cm‐1 is attributed to C‐C(HCl2) stretching mode. The in‐plane and out of plane bending vibrations are assigned and presented in Tables 3 and 4. All these assignments are agreed well with the reported literature values [39]. The CCC in‐plane bending and out of plane vibrations are described as mixed modes as there are about 10‐20% PED contributions mainly from C‐H in‐ plane and out of plane bending vibrations, respectively. In 3MPA the ring breathing mode corresponding to the a1g mode of benzene is assigned to the wavenumber observed in the infrared spectrum at 878 cm‐1 and in the Raman at 875 cm‐1 [29]. Arjunan et al. / European Journal of Chemistry 2 (1) (2011) 70‐76 73 Table 2. The calculated thermodynamic parameters of N‐(3‐methylphenyl)‐2,2‐dichloroacetamide employing HF and B3LYP methods with 6–311++G(d,p) and 6–31G(d,p) basis sets. Thermodynamic parameters (298 K) N‐(3‐methylphenyl)‐2,2‐dichloroacetamide HF 6–311++G(d,p) B3LYP 6–311++G(d,p) HF 6–31G(d,p) B3LYP 6–31G(d,p) SCF Energy (a.u) ‐1394.511 –1398.952 –1394.359 –1399.776 Total Energy (thermal), Etotal (kcal.mol‐1) 117.447 109.876 118.145 110.439 Heat Capacity at const. volume, Cv (cal.mol‐1.K‐1) 41.241 42.274 41.043 42.148 Entropy, S (cal.mol‐1.K‐1) 112.073 107.445 112.464 107.309 Vibrational Energy, Evib (kcal.mol‐1) 115.669 108.098 116.368 108.661 Zero‐point vibrational Energy, E0 (kcal.mol‐1) 110.272 102.844 110.989 103.428 Rotational Constants (GHz) A 1.187 1.161 1.189 1.159 B 0.290 0.286 0.289 0.286 C 0.271 0.267 0.270 0.267 Dipole moment (Debye) μx 1.297 1.699 1.340 1.641 μy ‐2.212 ‐2.176 ‐2.019 ‐1.907 μz 0.001 0.001 0.000 0.001 μtotal 2.564 2.761 2.423 2.516 Figure 3. FT‐Raman and theoretical spectra of N‐(3‐methylphenyl)‐2,2‐ dichloroacetamide. 3.3.2. C‐H vibrations The aromatic C‐H stretching vibrations are normally found between 3100 and 3000 cm‐1. In this region the bands are not affected appreciably by the nature of substituents. The aromatic C‐H stretching frequencies arise from the modes observed at 3062 (a1g), 3047 (e2g), 3060 (b1u) and 3080 (e1u) cm‐1 of benzene and its derivatives [40]. The C‐H present in the benzene ring of 3MPA gives strong to weak bands at 3104, 3043 and 3014 cm‐1. The vibrational modes observed at 3073 and 3063 cm‐1 in the infrared and Raman spectra are attributed to the C‐H stretching of ‐CHCl2 group. The aromatic C‐H in‐ plane bending modes of 3MPA are observed at 1163, 1138, 1042 and 975 cm‐1. The C‐H out of plane bending mode the compound are observed in the region 1100 to 600 cm‐1 and are presented in Tables 3 and 4. The aromatic C‐H in‐plane and out of plane bending vibrations have substantial contribution from the ring CCC in‐plane and out of plane bending, respectively. The C‐H(Cl2) in‐plane and out of plane bending vibrations are significantly mixed with CC in‐plane and out of plane modes, respectively. 3.3.3. Amide group vibrations The amide (–CONH–) group vibrations of the compounds investigated are correlated with N‐(phenyl)‐2,2‐dichloro acetamide (NPA), N‐(2‐methylphenyl)‐2,2‐dichloroacetamide (2MPA) and N‐(4‐methylphenyl)‐2,2‐dichloroacetamide (4MPA) vibrations [1,29]. Amide‐I band, the C=O stretching mode is the strongest band in the infrared spectrum and appears with diminished intensity in the Raman spectrum. In N‐phenylacetamide structure there is competition between the phenyl ring and the C=O for the lone pair of electrons of the nitrogen. The strong IR band observed at 1680 cm‐1 is assigned to the amide‐I band of 3MPA while the Raman counterpart is obtained as very strong band at 1678 cm‐1. The comparison of C=O stretching of 3MPA with that of NPA molecule reveals that the C=O stretching frequencies of the compound under investigation does not show significant variation from that of the parent compound N‐phenyl‐2,2‐dichloroacetamide. The N‐H stretching band of secondary amides seen in the infrared spectrum between 3370 and 3170 cm‐1. A weaker band may appear at about 3100 cm‐1 in secondary amides due to Fermi resonance of 1550 cm‐1. Thus the very strong band observed at 3245 cm‐1 in infrared spectrum and 3247 cm‐1 in Raman is attributed to the N‐H stretching of 3MPA molecule. The 4MPA shows the characteristic very strong N‐H stretching band at 3240 in the IR and at 3236 cm‐1 in Raman spectrum. In comparison with NPA, the N‐H stretching frequency of 3MPA is lowered by 20‐30 cm‐1 while between 2MPA and 3MPA there is no significant changes. The dipole moment measurements, X‐ray and neutron diffraction studies demonstrated that the trans conformer of N‐ phenylacetamide is the predominant and most stable [14,15,39,41‐42]. The influence of the ring substituent on N‐H stretching frequency of N‐phenylacetamide and its derivatives may be the resultant steric effect, direct field effects, hydrogen bonding and bond polarisation effects [43]. The steric effect of methyl substituent must be considered in conjunction with the conformations. The increase in N‐H stretching frequency may be expected in introduction of an o‐methyl group into the phenyl ring of N‐phenylacetamide. In the present investigation, it is observed that there is no increase in the N‐H stretching frequencies of 3MPA than that of NPA. This clearly confirms that the steric effect due to methyl group is not significantly operating on the N‐H stretching. The frequencies observed at 1554 and 1555 cm‐1 in 3MPA are ascribed to the amide‐II band, N‐H in‐plane bending mode. Shift in the lower frequency side with that of 2MPA (1588 and 1590 cm‐1) shows that the methyl group in 3MPA exerts less steric influence on the N‐H bond. The C‐N stretching mode, the amide‐III band, of 3MPA is assigned at 1335 cm‐1 in IR and Raman spectra, respectively. The spectral data indicates that no rise in C‐N stretching frequencies of 3MPA and there is no hyper conjugative influence of the methyl group towards the C‐ N bond. 74 Arjunan et al. / European Journal of Chemistry 2 (1) (2011) 70‐76 Table 3. The observed FT‐IR, FT‐Raman and calculated frequencies using HF/6–311++G(d,p) and B3LYP/6–311++G(d,p) force field along with their relative intensities, probable assignments and potential energy distribution (PED) N‐(3‐methylphenyl)‐2,2‐dichloroacetamidea. Sp ec ie s Observed wavenumber (cm‐1) HF/6–311++G(d,p) Calculated wavenumber B3LYP/6–311++G(d,p) Calculated wavenumber DPR Assign. %PED FT‐IR FT‐R Unscaled (cm‐1) Scaled (cm‐1) IR intensity Raman Activity Unscaled (cm‐1) Scaled (cm‐1) IR intensity A 3245 vs 3247 w 3863 3245 44.64 49.66 3594 3235 29.33 0.13 νNH 95NH A 3104 m 3419 3111 2.65 46.47 3242 3112 4.19 0.21 νCH 92CH A 3075 s 3368 3065 2.40 62.64 3186 3059 1.57 0.22 νCH 93CH A 3060 s 3342 3041 21.29 160.39 3183 3056 16.80 0.21 νC‐H(Cl2) 94CH A 3043 m 3323 3024 7.43 60.32 3165 3038 6.29 0.75 νCH 92CH A 3014 vw 3299 3002 17.04 54.84 3139 3013 12.93 0.28 νCH 94CH A 2998 m 2999 s 3247 2955 23.25 61.83 3106 2982 16.07 0.71 νaCH3 93CH A 2955 vw 2956 vw 3219 2929 23.33 72.52 3075 2952 14.93 0.75 νaCH3 96CH A 2922 vw 2923 s 3168 2883 35.18 184.68 3026 2905 29.16 0.03 νsCH3 92CH A 1680 s 1678 vs 1951 1678 379.46 30.32 1761 1691 339.16 0.18 νC=O 96C=O A 1801 1639 238.01 29.75 1651 1634 134.39 0.57 νC=C 92C=C A 1594 s 1595 vs 1778 1618 5.72 53.82 1632 1616 2.47 0.54 νC=C 91C=C A 1554 vs 1555 s 1732 1576 389.06 19.71 1584 1568 259.16 0.43 βN‐H 93NH A 1650 1502 159.81 4.28 1523 1508 145.34 0.22 νC=C 88C=C A 1482 m 1615 1470 12.42 4.60 1498 1483 14.41 0.74 δaCH3 91CH3 A 1447 m 1447 vw 1605 1461 6.99 9.82 1488 1473 7.95 0.75 δaCH3 93CH3 A 1432 w 1562 1421 43.17 2.52 1443 1429 42.11 0.66 νC‐C 85CC A 1410 vw 1538 1400 3.55 6.16 1417 1403 1.30 0.29 νC‐C 87CC A 1357 s 1456 1325 47.04 3.08 1348 1335 7.38 0.17 νC‐C 82CC A 1335 m 1335 m 1411 1284 215.28 32.94 1337 1324 80.19 0.10 νC‐N 84CN A 1283 w 1283 vw 1389 1264 22.57 8.97 1285 1272 22.29 0.17 δsCH3 90CH3 A 1260 w 1262 s 1381 1257 30.49 5.62 1273 1260 19.33 0.75 βC‐H(Cl2) 83CH + 12CC A 1358 1236 11.18 19.36 1253 1240 21.66 0.17 νN‐(C6H5) 87NC A 1217 vw 1315 1197 3.78 0.26 1229 1217 35.54 0.13 νC‐C 84CC A 1199 s 1200 m 1281 1166 13.60 11.47 1197 1185 3.32 0.34 γC‐H(Cl2) 77γCH + 16γCC A 1163 vw 1224 1114 3.93 5.87 1185 1173 1.92 0.75 βC‐H 75CH + 15CCC A 1138 vw 1193 1086 3.57 3.08 1119 1108 8.05 0.32 βC‐H 73CH + 18CCC A 1094 w 1092 w 1160 1056 2.47 0.17 1062 1051 2.89 0.75 ωCH3 66ωCH3 +21γCH A 1042 w 1112 1012 0.70 0.08 1038 1028 0.17 0.75 βC‐H 71CH + 16CCC A 1005 vw 1001 vs 1112 1012 2.27 1.65 1015 1005 0.99 0.57 ρCH3 77ρCH3 + 14CH A 975 m 976 w 1083 986 2.62 47.51 998 988 0.64 0.07 βC‐H 70CH + 20CCC A 1061 966 2.59 5.59 981 971 5.03 0.02 γC‐H 72γCH + 18γCCC A 938 w 942 vw 1017 925 5.30 0.38 920 911 2.98 0.75 γC‐H 74γCH + 20γCCC A 900 w 894 vw 980 892 5.67 1.14 916 907 4.85 0.57 γC‐H 70γCH + 22γCCC A 878 w 875 vw 965 878 14.72 0.11 868 859 11.80 0.75 βCCC 72CCC + 18CH A 918 835 52.76 7.35 802 794 0.38 0.75 γC‐H 69γCH + 21γCCC A 806 vs 804 vs 880 801 76.04 0.73 802 794 111.85 0.75 βC=O 85C=O + 12NH A 780 vs 777 m 870 792 46.40 17.25 796 788 14.15 0.07 νaCCl2 84νCCl + 12CH A 726 s 730 m 837 762 16.72 2.52 760 752 40.15 0.73 γN‐H 77γNH + 18γCO A 715 m 765 696 5.65 0.17 704 697 13.91 0.75 βCCC 74CCC + 14CH A 687 s 757 689 98.83 5.70 685 678 100.19 0.16 νsCCl2 82νCCl + 12CH A 658 vs 658 vw 733 667 2.16 6.25 648 642 1.88 0.75 γC=O 82γC=O + 14γNH A 566 m 567 m 634 577 1.81 1.77 584 578 12.27 0.75 βC‐C 65CC + 22CH A 542 vw 542 w 572 521 53.90 0.22 560 554 27.83 0.75 βCCC 68CCC + 18CH A 512 vw 521 m 568 517 2.81 8.07 534 529 1.48 0.18 βC‐N 72CN + 16CO A 531 483 31.16 2.08 492 487 31.46 0.57 βN‐C6H5 67NC + 19CCC A 462 vw 492 448 5.18 0.23 449 445 6.05 0.75 γC‐N 74γCN + 18γC=O A 430 vw 433 w 474 431 0.49 7.01 433 429 0.44 0.04 γN‐C6H5 68γNC + 16γCCC A 417 m 422 m 428 389 0.20 1.38 395 391 0.35 0.36 βC‐C(H3) 65CC + 21CH A 330 s 297 270 3.75 3.13 273 270 0.79 0.33 δCCl2 79CCl2 + 15CH A 293 w 295 268 0.18 1.89 273 270 3.28 0.75 γCCC 64γCCC + 20γCH A 248 m 289 263 1.50 2.23 267 264 0.60 0.56 γC‐C(H3) 62γCC + 18γCH A 231 vw 231 210 1.55 1.36 214 212 1.86 0.75 τCCl2 64τCCl2 + 24ωCCl2 A 188 m 191 174 5.86 1.14 175 173 6.38 0.32 ωCCl2 62ωCCl2 + 24τCCl2 A 101 vs 185 168 5.79 0.02 169 167 3.57 0.75 ρCCl2 70ρCCl2 + 18CH A 102 93 0.10 0.48 93 93 0.14 0.74 γCCC 65γCCC + 24γCH A 50 50 0.06 3.59 55 55 4.96 0.75 γCCC 61γCCC + 21γCH A 49 49 7.76 0.21 46 46 0.45 0.75 γCCC 63γCCC + 24γCH A 35 35 0.68 3.89 32 32 1.58 0.75 γCCC 62γCCC + 22γCH A 15 15 0.08 0.09 14 14 0.02 0.75 τCH3 90τCH3 a ν‐stretching; β‐in‐plane bending; δ‐deformation; ρ‐rocking; γ‐out of plane bending; ω‐wagging; τ‐twisting/torsion; IR intensities, KM/mole; Raman scattering activities, (Ao)4/(a.m.u); DPR: Depolarization ratio. The amide‐IV, C=O in‐plane bending of 3MPA is found at 806 and 804 cm‐1 in the IR and Raman, respectively. There is no significant shift in the C=O in‐plane bending, frequencies of 3MPA than that of NPA, 2MPA and 4MPA. The amide‐V, the N‐H out of plane bending is observed as strong and medium bands at 726 and 730 cm‐1 in 3MPA. The C=O out of plane bending of 3MPA is seen at 658 cm‐1. Both the amide‐V and amide‐VI out of plane bending modes of 2MPA, 3MPA and 4MPA is significantly raised than that of NPA. The PED calculations determine that the amide‐IV and amide‐VI bands possessing the character of N‐H vibrations by mixing. The amide‐V bands of 3MPA is significantly overlapped C=O out of plane bending vibrations. 3.3.4. Methyl group (−CH3) vibrations The symmetric, νs(CH3) frequency of 3MPA is established at 2922 and 2923 cm‐1. The asymmetric stretching of 3MPA, νa(CH3) is assigned at 2998 cm−1 under A' species. The depolarized frequencies seen at 2955and 2956 cm‐1 in the spectra of 3MPA are attributed to the νa(CH3) under A" species. The asymmetrical methyl deformation mode, δa(CH3) of 3MPA are observed at 1482 cm−1 under A" species while the band at 1447 cm−1 in the infrared spectrum is attributed to the methyl asymmetric deformational modes δa(CH3) in the A' species. Arjunan et al. / European Journal of Chemistry 2 (1) (2011) 70‐76 75 Table 4. The observed FT‐IR, FT‐Raman and calculated frequencies using HF/6–31G(d,p) and B3LYP/6–31G(d,p) force field along with their relative intensities, probable assignments and potential energy distribution (PED) of N‐(3‐methylphenyl)‐2,2‐choroacetamidea. Sp ec ie s Observed wavenumber (cm‐1) HF/6–31G(d,p) Calculated wavenumber B3LYP/6–31G(d,p) Calculated wavenumber DPR Assign. %PED FT‐IR FT‐R Unscaled (cm‐1) Scaled (cm‐1) IR intensity Raman Activity Unscaled (cm‐1) Scaled (cm‐1) IR intensity A 3245 vs 3247 w 3880 3259 45.55 42.16 3610 3285 27.71 0.14 νNH 94NH A 3104 m 3446 3136 2.23 49.81 3266 3135 3.75 0.21 νCH 95CH A 3073 s 3381 3077 2.37 69.75 3200 3072 20.90 0.28 νCH 92CH A 3060 s 3364 3061 26.72 165.61 3198 3070 1.08 0.19 νC‐H(Cl2) 93CH A 3043 m 3344 3043 9.11 64.85 3183 3056 7.44 0.75 νCH 94CH A 3014 vw 3320 3021 18.87 55.22 3156 3030 14.57 0.28 νCH 92CH A 2998 m 2999 s 3271 2977 22.67 63.84 3130 3005 14.89 0.73 νaCH3 93CH A 2955 vw 2956 vw 3242 2950 28.44 84.53 3098 2974 18.11 0.75 νaCH3 94CH A 2922 vw 2923 s 3186 2899 35.27 147.37 3042 2920 28.24 0.03 νsCH3 93CH A 1680 s 1678 vs 1983 1686 333.70 24.09 1796 1688 280.47 0.16 νC=O 95C=O A 1819 1655 189.05 29.89 1668 1651 103.31 0.59 νC=C 90C=C A 1594 s 1595 vs 1794 1633 8.30 42.05 1647 1631 4.54 0.54 νC=C 91C=C A 1554 vs 1555 s 1745 1588 397.63 15.99 1594 1578 259.58 0.38 βN‐H 92NH A 1666 1516 170.85 4.11 1537 1522 149.69 0.24 νC=C 89C=C A 1482 m 1626 1480 11.94 9.31 1510 1495 13.30 0.74 δaCH3 93CH3 A 1447 m 1447 vw 1615 1470 5.16 19.90 1500 1485 5.76 0.75 δaCH3 91CH3 A 1432 w 1577 1435 43.66 4.81 1456 1441 41.02 0.73 νC‐C 89CC A 1410 vw 1551 1411 3.74 12.30 1429 1415 1.10 0.41 νC‐C 88CC A 1357 s 1465 1333 42.42 1.77 1364 1350 20.98 0.23 νC‐C 90CC A 1335 m 1335 m 1421 1293 198.61 20.61 1344 1331 52.17 0.16 νC‐N 89CN A 1283 w 1283 vw 1391 1266 14.08 7.04 1296 1283 17.35 0.24 δsCH3 92CH3 A 1260 w 1262 s 1383 1259 34.48 8.94 1272 1259 28.74 0.75 βC‐H(Cl2) 81CH + 14CC A 1367 1244 14.90 13.43 1254 1241 27.46 0.32 νN‐C6H5 85NC A 1217 vw 1325 1206 2.41 0.13 1232 1220 24.74 0.70 νC‐C 88CC A 1199 s 1200 m 1291 1175 11.29 11.05 1202 1190 2.56 0.42 γC‐H(Cl2) 77γCH + 16γCC A 1163 vw 1237 1126 4.03 7.28 1194 1182 1.94 0.74 βC‐H 75CH + 15CCC A 1138 vw 1204 1096 3.78 2.71 1126 1115 7.83 0.52 βC‐H 74CH + 14CCC A 1094 w 1092 w 1165 1060 3.77 0.51 1066 1055 4.26 0.75 ωCH3 69ωCH3 +21γCH A 1042 w 1120 1019 1.63 0.42 1043 1033 0.10 0.75 βC‐H 70CH + 15CCC A 1005 vw 1001 vs 1118 1017 1.43 2.21 1016 1006 0.59 0.65 ρCH3 77ρCH3 + 15CH A 975 m 976 w 1090 992 1.66 33.14 991 981 1.12 0.13 βC‐H 72CH + 18CCC A 1067 971 1.98 2.53 986 976 3.63 0.04 γC‐H 74γCH + 16γCCC A 938 w 942 vw 1024 932 7.41 1.32 920 911 4.28 0.75 γC‐H 72γCH + 21γCCC A 900 w 894 vw 986 897 5.19 0.68 916 907 3.22 0.44 γC‐H 70γCH + 22γCCC A 878 w 875 vw 974 886 15.45 2.23 870 861 9.62 0.75 γC‐H 65γCH + 24γCCC A 917 834 53.35 8.06 805 797 15.24 0.75 βCCC 67CCC + 18CH A 806 vs 804 vs 889 809 68.96 1.36 804 796 89.83 0.75 βC=O 80C=O + 14NH A 780 vs 777 m 873 794 47.50 14.06 794 786 14.74 0.10 νaCCl2 78νCCl + 12CH A 726 s 730 m 840 764 18.57 3.27 760 752 44.55 0.71 γN‐H 77γNH + 16γCO A 715 m 770 701 2.38 0.40 706 699 4.55 0.75 βCCC 74CCC + 12CH A 687 s 756 688 100.69 5.26 687 680 102.91 0.22 νsCCl2 82νCCl + 12CH A 658 vs 658 vw 737 671 2.39 5.62 649 643 2.55 0.75 γC=O 80γC=O + 14γNH A 566 m 567 m 635 578 5.08 2.28 588 582 21.56 0.75 βC‐C 67CC + 20CH A 542 vw 542 w 578 526 66.20 0.88 563 557 29.29 0.75 βCCC 70CCC + 14CH A 512 vw 521 m 571 520 2.80 6.70 534 529 1.74 0.27 βC‐N 71CN + 15CO A 533 485 32.81 1.47 492 487 33.88 0.61 βN‐C6H5 67NC + 14CCC A 462 vw 492 448 2.90 0.47 450 446 3.33 0.75 γC‐N 76γCN + 16γC=O A 430 vw 433 w 477 434 0.62 6.87 435 431 0.50 0.06 γN‐C6H5 69γNC + 18γCCC A 417 m 422 m 430 391 0.37 1.72 395 391 0.42 0.42 βC‐C(H3) 65CC + 21CH A 330 s 299 272 0.03 2.95 277 274 0.36 0.75 δCCl2 77CCl2 + 18CH A 293 w 299 272 4.01 3.76 275 272 3.53 0.38 γCCC 65γCCC + 24γCH A 248 m 290 264 1.33 2.51 267 264 0.64 0.60 γC‐C(H3) 62γCC + 18γCH A 231 vw 232 211 0.85 2.21 216 214 1.13 0.75 τCCl2 67τCCl2 + 22ωCCl2 A 188 m 193 176 6.14 1.27 177 175 6.93 0.40 ωCCl2 65ωCCl2 + 24τCCl2 A 101 vs 188 171 5.81 0.08 172 170 3.33 0.75 ρCCl2 71ρCCl2 + 16CH A 103 94 0.08 0.52 95 95 0.16 0.74 γCCC 63γCCC + 22γCH A 50 50 0.01 5.35 54 54 4.45 0.75 γCCC 65γCCC + 21γCH A 42 42 8.25 0.58 45 45 0.29 0.75 γCCC 64γCCC + 24γCH A 38 38 0.22 5.14 42 42 1.55 0.75 γCCC 66γCCC + 22γCH A 13 13 0.08 0.07 17 17 0.08 0.75 τCH3 90τCH3 a ν‐stretching; β‐in‐plane bending; δ‐deformation; ρ‐rocking; γ‐out of plane bending; ω‐wagging; τ‐twisting/torsion; IR intensities, KM/mole; Raman scattering activities, (Ao)4/(a.m.u); DPR: Depolarization ratio. 3.3.5. CCl2 group vibrations When several chlorine atoms are attached to one carbon atom, the band is usually more intense and at high frequency end of the assigned limits. The C‐Cl absorption is observed in the broad region between 850 and 550 cm‐1. Thus, the strong and medium bands in IR at 780 and 777 cm‐1 cm‐1 are assigned to the asymmetric CCl2 stretching wavenumber of 3MPA. The symmetric CCl2 stretching is observed at 687 cm‐1 in 3MPA. The CCl2 asymmetric and symmetric stretching frequency of 3MPA does not show any appreciable variation from that of the corresponding frequencies in NPA, 2MPA and 4MPA. The in‐ plane CCl2 deformation vibrations and the out of plane CCl2 twisting and wagging modes are obtained in the low frequency region of the Raman spectra as medium to strong bands. These assignments are in good agreement with the literature values [1,44] and well supported by normal coordinate analysis. The CCl2 wagging mode significantly overlaps with CCl2 twisting mode and vice versa and also the in‐plane C‐H bending vibrations contributed to CCl2 deformation and rocking modes. 76 Arjunan et al. / European Journal of Chemistry 2 (1) (2011) 70‐76 Computed harmonic frequencies typically overestimate vibrational fundamentals due to basis set truncation and neglect of electron correlation and mechanical anharmonicity [45]. To compensate these shortcomings and to correlate the experimentally observed and theoretically computed frequencies for each vibrational modes of the compounds under HF and DFT‐B3LYP methods, scale factors are introduced [46‐54]. Initially, all scaling factors have been kept fixed at a value of 1.0 to produce the pure HF and DFT calculated vibrational frequencies which are given in Tables 3 and 4. Subsequently, in HF method the scaling factors 0.84 and 0.91 used for N−H and all other vibrations, respectively, except for C=O stretching. For C=O stretching, 0.86 and 0.85 were used with 6‐311++G(d,p) and 6‐31G(d,p) basis sets, respectively. In B3LYP level the correction factors 0.90, 0.96 and 0.99 for N‐H, C‐H and all other frequencies of 3MPA while for C=O, 0.96 and 0.94 with 6‐311++G(d,p) and 6‐31G(d,p) basis sets are the scale factors. The resultant scaled frequencies are also listed in Table 3 and 4. These are much closer to unity and thus the vibrational frequencies calculated by using the B3LYP functional with 6‐ 311++G(d,p) basis set can be utilized to eliminate the uncertainties in the fundamental assignments in infrared and Raman vibrational spectra. 4. Conclusion The molecular structural parameters, thermodynamic properties and vibrational frequencies of the fundamental modes of the optimized geometry of 3MPA have been determined from HF and DFT‐B3LYP methods. The FT‐IR and FT‐Raman vibrational frequencies of the compounds under investigations revealed close similarities in the magnitudes of the frequencies when compared with 2MPA and 3MPA, in spite of the fact that the methyl substituent in the phenyl ring are at different positions. The comparison of the fundamental vibrations, the following observations are made: The magnitude of C=O frequency variation is also not significantly influenced by the position of methyl group. In the present investigation, there is no increase in the N‐H stretching frequency of 3MPA than that of N‐phenyl‐2,2‐dichloro‐ acetamide, clearly confirms that the steric effect due to m‐ methyl group is not significantly operating on the N‐H. The comparison of other amide group frequencies did not show any appreciable variation in the respective wave numbers except the amide IV band, C=O in‐plane bending and the amide‐VI band, C=O out of plane bending mode of the compounds. 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