Mohan, S

Sundaraganesan, N

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•ndian J. P h ys. 66B (2), 213-219 (1992)Laser Raman and infrared spectra of 6-amlno- m-cresolS Mohan*" and N SundaragancsaviRaman School of Physics, Pondicherry University, Jipmer Campus,Pondicherry-605 006, India ;Received 5 September 1991, accepted 7 kovem ber 199iAbstract : The Raman spectrum of 6ramino-m-crcsol was recorded in ih c  region 100 4()()0 cm~^ and its infrared spectrum as mulls was also measured in the frequency range 2 5 0  40(X) cm  The spectra have been analysed assuming C, point group symmetry. Probable assignments to observed bands have been made with the help ol intensities and normal coordinate analysis. Ihc calculated normal frequencies are m good agreement with the experimental onesKeyw ords : l^ser Raman and infrared spectrum, 6-amino-m*crcsol, vibration'al assignmentPACS Nos : 33.10. Gx. 33.20. -t, 33.20. Dz, 78.30. -jRaman spectra of proteins give information not only on the structure of the main chain but also on the microenvironments of side chains (Harada and Takeuchi 1986). The important amino acid residues are tryptophan, tyrosine and phenylalanine which arc used in the Raman spectroscopic studies of protein structure, because the side chain vibrations of these aromatic residues are strong in the Raman spectra of visible light excitation and further more, they can be selectively enhanced by ultraviolet excitation (Harada and Takeuchi (1986), Rava and Spiro (1984), Johnson e/ a/ (1984), Rava and Spiro (1985), Copeland and Spiro (1985), Johnson er al (1986) and Asher et al (1986)). From the knowledge of characteristic aromatic side chain, we can interpret the vibrational modes of the Raman spectra of proteins. Takeuchi and Harada (1986), have studied the vibrational modes of tryptophan side chain and tyrosine side chain.The simplest model of the tyrosine side chain is p-cresol (4-mcihyIphenol). The Raman spectra of this compound and its three deutrated derivatives in the liquid state and theI.R. spectra in the liquid solution, vapour and solid states have been reported partially by Jakobsen (1965). Davy-Dova et al (1965) calculated the normal frequencies of out-of-plane vibrations and assigned some of the infrared and Raman bands. Green et al {1971) proposed complete assignments of fundamental frequencies for non-deutrated p-cresol. As the vibrational data for 6-amino-m-cresol is not available in the literature, the present investigation has been undertaken to provide complete spectroscopici information. TheAuthor for Corrctpondence 1992 I ACSvibrational analysis for 6-aniino-ni-cresol has-also been earned out through laser Raman and iiffirared spectra.The pure commercial sample obtained from M/s. Fluka A.G., Switzerland in soild form at room temperature was used as such. Raman spectra were recorded using a standard 90° configuration. The laser employed was a spectra physics Model 165 argon ion laser operating at 200-250 mW power on the 514.5 nm line. Scattered radiation was analysed with a Caiy-82 trible monochromator fitted with a polarizer and an-analyser. The frequencies obtained were correct to within ±  1 cm *. The infrared absorption spectrum o f  this compound was recorded in the region 250-4000 cm"' on Perkin-Elmer IR spectrophotometer 521 in KBr pellet. The frequency for all sharp bands are accurate to ± 1 cm"*214 SM okm m dN S u n daragan esanCH3Figure 1. Structure of 6 -amino-m-cresol.The structural formula o f  the compound is shown in Figure 1. The normal coordinate calculations were performed using the programme due to SchachtschneidcrTable 1. Initial and final sets of force constants of 6-amino-m-cresol (in units of mdync A mdyne lad"^ and mdyne A"' rad"^.Types of oonstantParameter CoordinatesinvdvedInitial 1‘inalDiagonal Stretching fo C-H 4.50 4.548oonstant u C-C Z85 2.729bending fa HCC 0.31 0.411ffi CCC 0.54 0.385fy CHC 0.29 0.312Inicmction Stretch- oonsuntsCHCC 0.19 0.198Laser Raman and ir^ ared  spectra o f  6-anino-m -cresol 215Table 1. (Contd.)Typesrf Parameter Coordinates Initial Finalconstant involvedconstants Stretch(«ij) u , cccc 0.06 0.156(opp) Im c=ccc 0.65 0.821foD CHCHbend-bend fau HOC HOC 0.04 0.042ceccCc 0.12 0.184fa y Heccftc 0.21 0.215HtecCe 0.08 0.124Stretch-bend fo a  \ c h h 6 c 0.25 0.261fo r  \ CHCHC 0.30 0.379fofi CHCCC 0.45 0.456c c c Ch 0.26 0.272crcCc 0.36 0.374Table 2. Vibrational assignments of 6<imino-m>cresol.IR frequency Laser Raman Calculated Assignment/Type and intensity frequency and intensity cm~^frequency (PED)cm ^ cm~^3465 — 3462 N-H asym. stretch3398 VS 3410 VS 3396 N-H sym. stretch3315 W 0-H stretch3120 S 2998 M 3118 CH3 asym. stretchA’ 3021 W 3019 C-H stretch (90)A' 2993 W 2988 C-H stretch (89)2988 M 2981 S 2981 C-H3 asym. stretchA' 2952 W 2943 C-H stretch (85)2851 S 2850 S 2841 CH3 sym. stretch1641 1622 0-H in-plane bendingA' 1621 1630 1624 C-C stretch (81)1610 1602 N-H torsionA’ 1605 VS 1607 S 1603 C-C stretch (80)A' 1600 1600 1596 C-C stretch (82)1541 W 1519 N-H scissoringA’ 1534 S 1534 S 1526 C-C stretch (79)1460 M 1449 CH3 asym. deformation— 1457 M 1447 CH3 asym. deformationA’ 1442 M 1431 C-C stretch (78)A’ — 1428 S 1422 C-C stretch (82)A’ 1403 S 1393 C-H in-plane bending1375 M 1361 CH3 sym. deformationA 1350 M 1341 VS 1329 C-NH2 stretch (6Q)A’ 1297 1288 VS 1275 C-OH stretch (60)A’ 1261 1270 S 1254 C-H in-plane bending (71)A’ 1240 S 1238 1229 C-CH3 stretch (68)A’1240 1231 0-H in-plane bending1160S 1165 VS 1152 C-H in-plane bending (76)Tabic 2. (C o n td .)216 S Mohan and NSundaraganesanTypeIR frequency and intensity cmLaser Raman frequency and intensity cm'^Calculatedfrequencycm"^Assignment/(FED)A"A"A"A"A"A’A’A’A’A’A"A"A"1103 1020 S 1010 MS 950 M891 S 850 842 S 810 S 810 S 733620 598 S 580 S 470 VS 386 W 357 331 W 315 S 29011091015 MS940 S 901 VS811 S 730 675 M601 S 581 S 475 VS 386 W 3492851101 N-H twist1012 0-H out-of-plane bending1011 C-C-C ingonal bending (85)941 0-H out-of-planc bending930 C-H out-of-plane bending (61)890 C-H oul-of-planc bending (68)839 C-H twist830 C-OH out-of-plane bending (64)801 C-H waggmg796 C-C out-of-plane bending (57)721 C-H out-of-plane bending (60)661 C-C out-of-plane bending (55)602 N-H wagging589 C-C in-plane bending (67)562 C-OH in-plane bending (54)462 C-C in-plane bending (72)365 C-NH2 m-plane bending (57)341 C-CH3 in-plane bending (55)321 C-C oul-of-plane bending (64)301 C-NH2 oul-of-plane bending (59)267 C-C!H oul-of-planc bending (61)(1969). Internal coordinates' for the out-of-plane torsional vibration are defined as Fecommended by International Union of Pure and Applied Chemistry (lUPAC). The valence force field was adopted for both in-plane and out-of-plane vibrations. The initial force constants were taken from similar benzene derivatives. This set of force constants was subsequently refined by keeping few interaction constants fixed throughout refincmeni process. The final force constants were presented in Table 1.The observed frequencies of the compound together with relative intensity, probable assignments and calculated frequencies are presented in Table 2. The observed spectra are explained on the basis of C, point group as shown in Figure 2.Assuming NH2, CH3 and OH groups as single mass point, the molecule under consideration would belong to C, point group. This simplified model gives rise to 30 normal mode of vibrations along with 18 additional vibrations due to substituent groups NH2, CH3 and OH. All the vibrations are active in both Raman and infrared spectra. Out of 30 nomal vibrations 21 A’ are planar vibration and 9A" are non-planar vibrations.The trisubstituted benzene which form the subject o f the present investigation give rise to three C-H stretching, three, out-of-plane bendings and three C-H in-plane bendihgs. The aromatic stmeture shows the presence of C-H stretching vibrations in the region' 3000-L aser Raman and it^ a re d  ^ x c tra  o f  6-amino-m~cresol 2173100 cm "\ which permits a ready identification for this structure. In this region, the bands are not appreciably affected by the nature o f  substituents. The frequencies 3021, 2993 and 2952 cm"* in 6-amino-m-cresol have been assigned to C-H stretching modes. The rest o f the vibrations, viz., three C-H in-piane bendifigs and three C-H out-of-plane bendings o f 6- amino-m-cresol molecule are given in Table 1. They are in good agreement with literature values (Silver and Wood 1964). jFigure 2. Infrared and Raman spectra of 6-amino-m-cresQl.It is noted from the literature that a strong band around 1200 cm"* appears due to valence oscillations in toluene and substituted toluenes. Hence, the strong band at 1240 cm * in 6-amino-m-cresol is assigned to C-CHa stretching mode. The bands at 357 and 290 cm"* in 6-amino-Ri-cresol have been assigned to C-CH3 in-plane,bending and C-CH3 out-of­plane bending respectively. This conclusion agrees well with the literature values (Sing et al 1966, Padhye and Vilodkar 1959).The C-NH2 stretching frequency appears at about 1300 cm"*. The Band at 1350 cm"* in 6-amii)o-m-cresol is assigned to this mode. The bands at 386 and 315 cm*' have been assigned to C-NH2 in-plane bending and out-of-plane bending tespectively.According to Bellamy (1959), in primary aromatic amines the N-H stretching vibrations occur in the region 3300-3500 cm"*. According to this, the bands at 3465 and 3398 cm"* in 6-amino-m-cresol have been designated to rqiresent the N-H stretching modes. 77te higher value in the above case is assumed to be asymmetric stretching while the remaining to the symmetric stretching. The NH2 s c i^ r in g  mode normally lies in the2B as)218 S M ohan and N  Sundaraganesanregion 1590-1650 cm“‘ in primary aromatic amines (Bellamy 1959). This seems to fall at 1541 cm“* in this case. NH2 wagging mode is assigned to the band at 620 cm"‘ by analogy with aniline (Evans 1960).The CH3 active asymmetric stretching modes have been assigned to the lines at 2998 and 2981 cm'* in the Raman spectra of the solid and CH3 symmetric stretch is assigned to the line at 2850 cm'*. The three deformations o f the methyl group are observed in the Raman spectrum of solid at 1460 and 1457 cm * for the antisymmetric deformation and 1375 cm * for the symmetric motion. These observation agree very well with Durig ei al (1990).The C-OH stretching frequency for this molecule appears at 1288 cm'* in Raman spectrum. OH stretching vibration gives rise to a Raman band at 3315 cm'* and O-H in­plane bending frequency have been found in 6-amino-m-cresol at 1641 and 1240 cm *. The O-H out-of-plane bending modes gives rise to frequency at 1020 cm * and 950 cm '. These observation are also in agreement with Pasquier et a l (1990).In order to obtain a more complete interpretation of the vibrational spectrum and 10 determine the degree o f mixing o f normal modes, a normal coordinate analysis o f 6-amino- m-cresol was carried out. This analysis was made using the W ilson’s GF matrix method (Wilson et a l 1955), employing the programs developed by Schachtschncider (1969). The G matrix was calculated using the su-uciural parameters C-CH3 = 1.541 A, C-H = 1.073 A, C-C = 1.527 A, C-OH = 1.260 A and C-NH2 = 1.47 A. Initial values for the force constants were also taken from benzene derivatives. From the modified valence force constants the observed frequencies were fitted to 23 cm * (8.0%) for the 6-amino-m-cresol.In the present study, a coAiplcle vibrational assignment and the analysis o f 6-amino- m-cresol are available using the frequencies obtained from infrared and laser Raman spectra on the basis o f Cj symmetry.A ck n o w led g m en tOne o f the authors (NSG) thanks CSIR for the award o f Senior Research Fellowship.ReferencesAsher S A, Ludwig M and Johnson C R 1986 J. Am. Chem. Soc. 108 3186 Bellamy L J 1959 Ths Infrared Spectra o f  Complex Molecules (New York : John WUey)Bellamy K J 1959 infrared Spectra ofOrgainc Molecules (New York ; John Wiley)Copeland R A and Spiro T G 1985 Biochemistry 24 4960Davydova N I. Zhigunova I A and Ignaateva M A 1965 56 1077; 1965 Opt. Spectrosc. USSR IS 605 Durig J R. James C G and Hizer T J 1990 J.Raman Spectrosc. 21 155 Evans J C 1960 Spectrochim. Acta 16 428Green J H S. Harrison D J and Kynaison W 1971 Spectrochim Acta 21A  2199Harada I and Takeuchi H 1986 Spectroscopy o f  Biological Systems, Advances in Spectroscopy Vol 13 eds Clark R J and Hester R E (Chichester : Wiley) pi 13Johnson C R, Ludwig M» DDonell S and Asher S A 1984 J. Am. Chem. Soc. 106 5008 Johnson C R, Ludwig M and Asher S A 1986 J. Am .C hem . Soc. 108 905 Jakobsen R J i965 Spectrochim Acta 21 433Padhye M R and Vilodkar B G 1959 J. Sci. Indus Res. MB 45Pasquicr B. Le Calve N, Rozycki A and Novak A 19907. Raman Spectrosc. 21465Rava R P and Spiro T G 1984 7. Am. Chem. Soc. 106 4062-  1985 7. Pkys. Chem. 89 1856Schachtschneider J H1969 Technical report (Shell Development Company. EmeiyviUe)Silvpr H G and Wood J L 1964 Trans. Faraday Soc. 60 5Smg V B, Sing R N and Sing IS 1966 Spectrochim. Acta ]2A 927Takeuchi H and Handa 11986 Spectrochim Acta 21 433Wilson E B, Decuu J C and Cross P C1955 Molecular Vibripions (New Yoik : McGraw Hill)Laser Raman and ir^ared spectra of6-amino-m’Cresol 219

Laser Raman and Infrared Spectra of 6-Amino-M-Cresol

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Laser Raman and Infrared Spectra of 6-Amino-M-Cresol

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