Rai, S B

Rai, Vineet Kumar

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(3). 351-354 (2003)o A ^ t5:< IJPBoteOvertone absorption spectra of some aliphatic aminesVineet Kumar Rai and S B Rai*Laser and Spectroscopy Laboratory. Department of Physics, Banaras Hindu University, Varanasi-221 005. IndiaE-mail : sbrai®banaras.crnet inReceived 30 December 2002, accepted 5 February 2003Abstract The infrared and near-infrared overtone absorption spectra of ethyl, n-butyl and isopropyl amines have been studied in pure and diluted (nriii Vibrational frequency and the anharmoniciiy constants for the C-H. and symmetric and asymmeinc N-H stretching vibrations for the three iimlcLules have been determined using local mode model A dilution study clearly indicates the presence of intennolecular hydrogen bonding in all theihru' Lascskeywords Absorption spectra, aliphatic amines, intermolecular hydrogen bonding, vibrational frequency, anharmonicity PACS Nos. 78.30.Jw. 33.20.Ea. 42 65 KyRecently, we have studied the vibrational absorption spectrum aniline and its derivatives near 2500-16500 cm ' region[l-3]. kvcral bands either due to overtones or due to combination of low frequency fundamentals of N-H and C-H stretch or other nhralions have been observed. The N-H stretch vibration clearly shows the presence of peak due to symmetric and asymmetric “iircich vibrations, the intensity of the asymmetric stretch being h^ghtly smaller than the symmetric one. Our curiosity to see the presence of N-H symmetric and asymmetric peaks in their funuamcntal and overtone bands and the intermolecular hydrogen bonding in other systems have led us to study these aliphatic amine molecules in the IR and NIR regions. A detailed l^udy of these in the 400-13000 cm * region are reported here. To ihe best of our knowledge, the overtone bands of these [Molecules have not been studied so far except the old work of l^ oiffand Gamer [4].T^he samples of ethyl, n-butyl and isopropyl amines were ‘^hUined irom BDH (India). The reported purity of these ‘^ '^ '^ pounds were 99% and they were used as such for experiment '*'‘ihout any further purification. The NIR spectra were recorded Lambda-19 UV-Vis NIR double beam spectrophotometer i''' for fundamental band, a JASCO FTIR-5300 ■^photometer was used. The spectra were also recorded the sample with carbon tetrachloride as solvent. For" s^ponding Authoreach sample, the cuvette was cleaned and rinsed properly to avoid the impurity of other compound. Several scans were made for each sample to avoid shift of peak positions and any other uncertainity. All measurements were made at room temperature (30'*C)with samples path length I cm.The absorption spectra of these compounds were recorded in between 400-13000 cm ' region. A part of the absorption spectrum of n-buiyl amine is shown in Figure 1. The spectrum of other compounds are similar to it. The spectrum shows several peaks in 2800-3000 cm ' region in all cases due to the presence of non-equivalent C-H Morse oscillators which give slightly shifted peaks in all the three compounds. There are two peaks 60-80 cm ' separated from each other in the 3300-3400 cm*' region. These peaks are assumed to be due to the asymmetric and the symmetric N-H stretch vibrations. The intensity of the two peaks are nearly the same in contrast to the case of aromatic compounds (aniline and its halo and alkyl derivatives) where the intensity of the two peaks are very different from each other. There also appears some weak bands in this region and they are perhaps due to the combinations. The 5800-6800 cm'' is the region where first overtone due to CH and NH bands are expected and in the spectrum of all the three molecules, this region appears very much crowded. Though both the peaks for the N-H vibration (but the asymmetric stretch peak now appears weak than the symmetric stretch) appear in this region, the number of©2003IACS352 Vineet Kumar Rai and S B Ratpeaks for CH stretch vibrations are reduced. Some very weak bands appear here again due to the combination of first overtone of CH and NH stretch or with other fundamentals or with theirFigure 1. The vibrational absorption spectrum of n-butylamincdeformations. The number of peaks arc further reduced as we go to the higher harmonics so that only one peak appears for the 3<—0 and 4<—0 transitions for the C-H stretch vibration. The asymmetric peak of the N-H vibration becomes too weak to be detected for4<—0 transition. Although some combination bands appear in this region, their intensity is very small. The band width of the peak increases every time as we go to the higher harmonics. The frequency of the bands and their vibrational assignments for the three molecules are given in Table 1. The spectrum of n-butylaminc and the assignments of the bands observed is shown in Figure 1.Table 1, Transition frequencies (cm ') for ethyl.n-bu(yl and isopropyl aminesSample 1 ^ 0 2<-0 3<-0 4<-0Ethyl amine (C-H) 2950.1 5772.8 8430 5 11022 2(N-H sym ) 3338.2 6536.7 9581.8 12407.2(N-H asym.) 3393.4 6684.3 9840.1N-butyl amine (C-H) 2928.2 5698.7 841 1 0 10934.3(N-H sym.) 3323.6 6544.3 9575.9 12440.1(N-H asym.) 3379.6 6691 4 9827 3Isopropyl amine(C-H) 2955.3 5769 3 8431.3 11025.6(N-H sym.) 3317.8 6503 8 9557.1 12397 1(N-H asym.) 3387.1 6712.0 9860.1vibration in all the three molecules. However, only one peak appears for second and third overtones as if the energ\ corresponding to all the non-equivalent C-H oscillators aic concentrated in only one band. A Morse plot in between E/\Figure 2 . A  M o r s e  p lo t  E /v  versus v f o r  n - b u ty l u r n in eversus v for n-butylaminc molecule is shown in Figure 2 The transition frequency for different vibrations for all the th ree molecules were fitted by least square fit method using local mode modelA E y  = Av -I- B v ^ ,where is the transition frequency, v is the vibrational quantum number and A and B are the fitting constants related with actual molecular constants as w jc = -  B and w -  A -  B. The andf r  e ^w X values and the errors estimated for all the three vibrationsf  rin the three molecules, are given in Table 2. The low irequcnc\ fundamentals and the combination bands and their assignments are given in Table 3 (a), (b) and (c). A comparison ot these values in the three molecules indicate that they are nearly same The combination bands may be either due to local mode-local mode combination or due to normal mode-local mode combination or due to normal mode-normal mode combinations In our case, we observe only normal-normal and normal-localTable 2. Vibrational frequencies, anharmonicity constants and dissonJin’l energies for the C-H stretch vibrations in ethyl,n-butyl and isoprop'SampleEthyl amine N-butyl amineAs mentioned earlier for fundamental and first overtone transitions, two to three peaks arc observed for C-H stretchA -B= W.X. =A-B 0  = w V4 w(cm “) (cm') (cm‘) (cV) _3004.7 62.5 3067.5 4.6±4.6 ±2.3 ±6.9 ±0 152995.1 65.3 3060.4 4 4± 11.1 ±3.2 ±14.3 ± 163001.3 61.6 3062.9 4 7±7.4 ±2.1 ±9.5 ± 13l-in S-H stretch v ib ra tio nS am plf A - B =  w Xl! tl w  = A - B D  =  w(cm ' ) (cm ' ) (cm ' ) ( c V )Bihyl a m in e 3 4 1 3  5 7 3 . 0 9 3 4 8 6  5 5 . 1 5± 1 . 6 ± 0 . 6 ± 2  2 ± 0 , 03 4 5 7 . 5 5 8  9 3 5 1 6 . 5 6  4 9± 6 . 3 ± 2 . 4 ± K  7 ± 0  2N -buivl a m in e 3 4 1 8 . 1 7 6  5 3 4 9 4 . 6 4 . 9 5± 8  9 ± 2 . 6 ± 1  1 .5 ± 0 .13 4 5 6 . 2 5 9  5 3 5 1 5  7 6  4± 1 2  6 ± 4 . 7 ± 1 7  3 ± 0 . 4Iso p ro p y l 3 4 1 6 . 2 7 8 . 8 3 4 9 5  0 5  0 8\i iu n o ± 7  4 ± 2 .1 ± 9 . 5 ± 0  43 4 6 3 . 4 5 8  2 3 5 2 1  7 6  6± 1 3 . 3 ± 5  0 ± 1 8 . 4 ± 0 . 5Tabic 3 ( a ) .  C o m b i n a t i o n  b a n d s  in  e t h y l  a m i n e ,  n - b u ly l  a m in e  a n d  isopropyl a m in e  a n d  t h e i r  a s s i g n m e n t s .ruqucnL'ytcm ')S‘)() 01115. 1280I4fi() 0 144 W)U)20 0:ssii 0 0S4H() 1 MU 1 ?hM 7ns 2 HI 1)7 Sr*ble 3 (b).A s s i g n m e n t sC - C  s t r e t c h  ( b e n d )( b e n d )( b e n d )N H  d e f o r m a t i o nO v e r t o n e  o f  t h e  a s y m m e t r i c  C H ,d e f o r m a t i o nC o m b i n a t i o n  b a n d' 'ch+28^ 12''rH+6cH'^^ ch'*^ chIf^ i-'qucncylcm ') A s s i g n m e n t sm  0 C - C  s t r e t c h120 , 1 2 7 4 ( b e n d )1462 0 ( b e n d )1494 0 ( b e n d )1625 0N H  d e f o r m a t i o n7KH5 0O v e r t o n e  o f  t h e  a s y m m e t r i c  C H ^  d e f o r m a t i o n^^ 7^0 0C o m b i n a t i o n  b a n dM14 2« c H + 2 8 r „<^780 f,7:i7o S7107 4 *^748 32'>c h + « ch2 ( '» c h -*«c h ) ■? aliphatic amines 353T a b l e  3  ( c ) .F r e q u e n c y  ( c m ') A s s i g n m e n t s8 0 2  0 C - C  s t r e t c h i n g8 0 9 , 0 C - C  s t r e t c h1 0 8 6 ,  1 1 3 1 ,  1 2 4 5 ( b e n d )1 4 4 7 6^.^, ( b e n d )1 4 6 2  0 ( b e n d )1 6 0 8  0 N H  d e f o r m a t i o n2 8 7 0  0 O v e r t o n e  o f  t h e  a s y m m e t r i c  C H ^  d e f o r m a t i o n2 9 6 .S  0 C o m b i n a t i o n  b a n d5 4 1 3  4 ' ' . H + 2 6 r „6 2 8 5  0 C'll7 1 2 4 . 3 2\)^7 3 4 2  38 1 3 0 . 4 2 ( « r „ + 6 , „ )combinations. The frequency of combination bands in the case of normal-local combination is given as^ ( v ,  , V 2 ;0 )  =  +  V , i ? |  ) ±  V 2 (  ^ 2  + V 2 ^ 2 ) ' * ' ^ i ' ' 2 ^ c -where A j and A „ ^^ re the mechanical constants for the two vibrations and X is the coupling coefficient.The calculated values of the off-diagonal local-normalinteraction constant for (u arc given in the Table 4.CH three moleculesT a b i c  4 .  O f f - d i a g o n a l  L o c a l - N o r m a l  c o u p l i n g  c o e f f i c i e n t  XG r o u p s  in v o l v e d  in  c o u p l in g X ,E t h y l  a m in e  ) -  1 2 .5 1n - B u ty l  a m in e  + 5^,^,) -  2 5  5 3I s o p r o p y l  a m in e  ) »  15  3 7Overtone bands due to N-H stretch vibrations :The N-H stretch vibration show well resolved double peak, the intensity of the one component lying in the lower energy side is smaller than the other one for the harmonics. The frequencies of the bands are given in Table 1. The vibrational frequency and the anharmonicity constants for the symmetric and the asymmetric stretch vibrations from the fit are given in Table 2. It is noted that the vibrational frequency and the anharmonicity constants for the symmetric stretch are identical for all the three cases. A similar thing is with the asymmetric vibration. The frequency of asymmetric stretch is larger than symmetric stretch. It is interesting to note that as we go from symmetric to asymmetric vibration, the vibrational frequency though changes by 1-2%, the anharmonicity constants change by >20%. It is much smaller in the case of asymmetric stretch vibration.354 Vineet Kumar Rai and S B RaiTable 5. EITect of dilution on the NH symmetric stretch vibration in the three aliphatic amines.Dilution (%) l<-0 24-0 34-0100 3338.2* 6536 7* 9581 8*3323 6^ 6544.3# 9575 9#1317.8* 6503 8* 9557 1 *50 3356 2* 6550 7* 9587,1*3135.4e 6556.6# 9585 1 #3.141 0* 6520.0* 9571 0*20 3366 1* 6560..1* 9591 3*3345.5# 6565 5# 9590.4#3356 4* 6534 4* 9580.1*10 3376 8* 6564.4* 9595.3*3353.5# 6570 0# 9593 8#3362 2* 6544 8* 9585 2*I 3384.1* 6566 2* 9598.1*3360 7# 6574 6# 9596.5#3365 4* 6549 6* 9586 4*0.1 3389.3* 6568.5* 9600.2*3367.5# 6577 1 # 9598.4#3369.6* 6551.7* 9587.0*increases. As a result, the monomer peak starts dominating a overall peak shifts. At higher dilution, most of the molecules in monomer form and it shows a saturation.♦- N-H stretch frequencies for ethyl amine♦ - N-H stretch frequencies for n-bulyl amine,♦ • N-H stretch frequencies for isopropyl amineWe also recorded the spectrum of the three molecules at different dilutions (100%,50%,20%, 10%, 1 %,0.1 %)using carbon tetrachloride as solvent. The spectrum of the n-butylamine at different dilution is shown in Figure 3. One can sec from the Figure that the N-H peak clearly shows a blue shift as we go to higher dilution. However, the shift is much smaller compared to the shift observed in the compounds containing OH group (see Table 5). The compounds containing OH group are strongly hydrogen bonded through the electronegative element O and forms higher oligomers. On dilution, the hydrogen bonds break and monomers arc formed which give sharp peaks nearly 250 cm shifted in the higher frequency side. In the compounds containing amino group, the hydrogen bondings are relatively weak as N is less electronegative than 0 . In this case also on dilution, monomers are formed very much similar to the earliar case. Our measurements show that these monomers arc only 40-50 cm ' shifted in the higher frequency side from the associated peak and therefore in this case, they arc not well- resolved with the associated peak. The intensity of the associated peak decrease with dilution and that of the monomerFigure 3. Effect of dilution on the absorption spectrum ot n-buiylamintAs we go to the cases of higher overtones the shift decrease This demonstrates the effect of chlorine atom from CCl on N H4bond as the amplitude of N-H bond increases. This is again very much identical to what have been observed in the molecules containing hydroxyl radical [5]AcknowledgmentsAuthors are grateful to the Council of Scientific & Industrial Research and the Department of Science & Technology, New Delhi for financial assistance.References[ 1 ] J Vipin Prasad, S B Rai and S N Thakur Indian J Phys 691131^(1995)[2] Vinecl Kumar Rai, D K Rai and S B Rai Specirodwn 1299 (2003)[3] Vineet Kumar Rai. A K Rai, D K Rai and S B Rai Specnvil^ '^" Acta A (in press)[4] H Wolff and G Gamer J.Phys.Chtm . 76 871 (1972)[5] P K Srivastav, D K Rai and S B Rai Specirvchim Aciu A561-* (2000)

Overtone Absorption Spectra of some Aliphatic Amines

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Overtone Absorption Spectra of some Aliphatic Amines

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