Shukla, Jaya V

Singh, V B

Upabhya, K N

IACS Institutional Repository

56VIBRATIONAL SPECTRA OF THE THREE ISOMERIC DINITROBENZENES(MiB8) J A Y A  V . S H U K L A , V . B . SJNGH akd  K . N . U P A B H YADkpaktmknt of Spectkosccwy Banaras Hindu XJNivEKsity Varanabi-5, India.{Received M arch  26, 1968; Rembmitted July 26, 1968)ABSTRACT. The infrared absorption spectra of the three isomeri(i dinitrobonz<*n<\^  have boon recorded in the region 700-4000 (‘m 'l on a Perkin-Elnicr double beam infrared spectro- j)li()tomotor (Model 13-U) v.*ith NaCl prism using KBr pellet te'Tmi(ine. The vibrational u^ 'SJgiimonts of the observed froqiieneiob have bot.'ii nnule by assuming point gr<»up (or o-aml m-dinitrobenzcm>s and JI2// “  V/, point group lor p-dinitrobenzene.I N T K 0  D U C 1 0  NA cousiderablo amount of data has been publishod on the N - 0  stretching Vibrations of tlu^  nitiT> group (Brown ii)55; Kross and Fassol 19/>G). The t ibi atioiial spectrum of nitrobenzeme has bf‘on investigated b}^  Green d al (19()1), who have proposed assignnnuits of vibrational freqiuTi(‘i(*s to various modes of vibration of tlie molecule. Studi<‘s of the infrared spectra of tiu*. tinee isomeric dinitrobouzenes luive botm made by Katritzky and Simmons (1959), Conduit (1959) and Pristera H al (19G0), but none of these workers hits jirestmted a complete analysis of all the observed bands. Therofoio we proposed to study the infrared absorption spc'cti a of the tlircc' isomeric dinitro- bciizones. The Raman spectra of thosti compounds have lanm repeu’tod in tin*, Landolt Bomsteiri table (1951) without polarisation, measurements.E X  1* E R I M E X T A LThe chemicals used were mauufaetim'd by B.l .^Jhi. Those were of pun? (jiiality and are solid at room temperature.The infrared absorption spectra of o-, m- and ^.j-diuitrobenzones Iiav(‘. be(ui I'crorded in the region 700-4000 ciu'^ on a Perkin-Elmer double beam infrari^d •s])(‘ctrophotometor (Model 13-U) with NaCl prism miiig KBr pellet toehniqiUL rile pellets wore prepared by taking a fewv milligrams of the substance and mixing it with a email amount of potassium bromide. The mixture was then gi'ound to a tiuo powrder in an agate mortar and pressed in a sptnual di(^  lor few minutt s^ imd<rr ])n\ssure of about 40 tons per sq. inch in a hydraulic press. The accuracy of bieasuromonts is 2 ciu'^  ^ botAveen 700-1500 4 em''  ^ between 1500-3000 cm ^invi l()cm~^  above 3000 cni“^611R E S U L T S  AND D I S C U S S I O NThe traces of infrared spectra of the three dinitrobenzenes are given in figures I, 2, and 3 respectively. Tlio infrared and Raman frequencies alongwith tlicir relative intensities and proposed assignments are given in tables 1, 2 and 3 res- Ijoctivoly for the throe dinitrobenzenes.{Miss) J. F. Shukla, V. B. Singh and K. N. Upadhya 612Figure 1. Infrared abaorpiion spectrum of o-dinitro Ijeiizetio (soliil pliase)Figure 2. Infrared absorption spootrum of m-dinitro benzene (solid phase)Figure 3. Infrared absorption spectrum of p-dinitro benzene (solid phase)Table 1. Vibrational fnuiuoncies and their assignments for o-dinitrobonzene5 1 3  Vibrational Spectra o f DiniirobenzenesRaman(solution)Infrared (KBr pellet) present workAssignmentcm“^ Int. cm”^ Int.685 (0) ai C - — C i.p. bending700 (8) bi fundamental727 (8) bj C— C— C o.p. bonding754 (0)789 (8) l>i C—H o.p. bending841 (7) bt C—H o.p. bondingS58 (1) 864 (5) 0-1 NO2 i.p. bonding887 (2)915 (1) 924 (2) bi C H o.p. bonding969 (3) bi C—H o.p. bonding1000 (3) Oj C— C— i.p. bending1041 (1) 1041 (4) ai C—C stretching(ring breathing)1071 (4) bj C—H i.p. bending1148 (6) ai C—H i.p. bending1192 (3) Ai C“ H i.p. bending1209 (5)1293 (8) bg C—H i.p. bending1319 (8) ai C—N stretching1361 (fl) 1354 (10) ai N =5 0  sym. stretching1414 (4) ba C 0 stretching1456 (6) a-i C — C stietching1537 (0) 1526 (10) N =  0  asym. stretching1607 (0) 1608 (3) aj C =  C stretching1639 (2) Ai 789 +  841 16301662 (2) Bi 789+864 -- 16531742 (2) 700 [1041 =  17411846 (2) B, 700+1148 =  1S4S1964 (2) Bi 924 +  1041 19651998 (2) Ai 685 +  1319 -  20042170 (2) Bi 841 +  1319 - 21602246 (2) Bi 789 1 1456 -  22462374 (3) Bi 924+1466 =  23802419 (3) Bi 969+1456 =  24252679 (3) Ai 1319 +  1354 -  26732883 (5) Ba 1364 + 1626 ^  28803099 (6) ba C—H stretching3780 (4) Bj 685+3098 =  37833882 (3) Ai 1354+1626+1071 =  39513942 (3)N.B. : i*p. =  in-plane; o.p. =  asym. =  asymmetricout-of-plane; sym. =  symmetric andTable 2. Vibratioual IVcquoneics and their as. i^gmixorits for m-diaitroboiizene{Miss) J . V. Shukla, V. B. Singh and K . N . Upadhya 6 1 4Raman( f lo lu t io i» )Infrared (KBr pellet) I>reaont work Assignmentc*ni“ ^ Int. ('m~i Int.08.‘! (10) ill ^  i-P* bonding702 (0)724 (ft) Uj ( - - C -C o.j>. bonding760 (2)791 (2) bj C -H o.p. bondingS17 (7) b, C- -H o.p. bondingS40 w S37 («) til NO2 i.p. bonding000 W 91 f) (7) bj C- H o.p. bonding944 (2) bi H o.p. bonding1005 (4) 1003 (S) ai C — C stretching(ring breathing)1027 (4) ai C-- C -C  i.p. bonding1067 (K) bo r  H i.p. bending1092 («)1128 (4)1149 (0) 1145 (fi) ai (< —n i.p. bonding1172 (5) ai C -H  i.p. bending1210 (1) 1212 (5)1273 (7) ba C- -H i.p. bending1363 (0) 1347 (8) ai C—N stretching1365 (3) 1357 (10) aj N — 0  sym. stretching1440 (0) 1441 (S) ba 0 “  C stretching1476 (7) aj C =  C stretching1510 (9) ba C — C stretching1538 (4) 1530 (10) ba N — 0  asym. stretching1600 <3) 1603 (7) bi C C stretching1694 0 ) Ai 79M-915 =  17061758 (1) Bi 724 +  1027 =  17611820 (1) Ai 2 x9 1 6  -- 18301904 (2) Bi 724 +  1172 18961996 (2) Ai 2 X 1003 -= 20062252 (3) Bi 915+1347 == 22622359 (3) Ai 10034 1367 =  23602383 (3) Ai 1027 +  1367 =  23842431 (3) Ba 1067 +  1367 === 24242492 (3) Ai 1146+1347 =  24932888 (6) Ba 1357 +  1630 «  28873099 (6) ba C— H stretching3461 (S) Ba 1027 +  1357 +  1067 =« 34613674 (2) Ba 1067+1367 +  1146 =  35703928 (4) Ba 837 +  3099 «  3936N ,B . : i.p. — in-plane; o.p. out-of-plane; sym. ~ symmetric; and aaym, =* asymmetric,5 1 6 Vibrational 8ps,ctra of Dinitrobenzen^sTable 3. Vibrational frequoncioa and their aaaignmonts for p-dinitrobenzonoRaman(solution)Infrared (KBr pellet) present workInt.9061106(0)( 1 )13581685(4)(1)710784800820839873101011041144116111811213127012821319134313821407147815521580162716991800194222052262236024622840292131093474381739243974Int( 8 )( 2 )(3)(4) ( 8) (7)(4)(5)(2)(3)(3)(3)(5)(5)( 9)( 10)(5)(3)(4)(9)( 6) (2)( 1)( 1 )( 2) (2)( 2 )(3) ( 1)(4)(4)(5)(6)(4)(5)(4)Assignmenti>jtt H o.p. bondingb ,4 CJ -H  o.p. bonding1)11, N(>2 i.p. bending bjM NO2 i.p. bending baff C—H o.p. bending bau C— C ~r i.p. bending C—H i.p. bendinga>jg C—C stretching(ring breathing)hitt C—H i.p. bondingbit, C ■= C stretching f>2u C—N stretching had N — O sym. stretching C—H i.p. bending haw C — C stretchingbitt C “  C stretching bit, N — O asym. stretching ni^  C — C stretching Bid 710 +  906 =  1616;h.iu X ba(, == BittBi 800x906 =  1700; haw XBat* 1104 +  1106 =  2210:bat, X  Oj, — B 21,Bid 1106+1161  ^ 2267;Oy X  b id  ”  B idB ,„ 1010+1358 =- 2368:bau  ^bjj, =  B|f,Bid 1104+1358 -- 2462; ba« X l)3j, — Bit!Bad 1358+1478 =  2836; X bj fi =  BauBad 1343+1680 =  2923;bao ~ Ba«bad C—H stretching; i.p. =  in-plane; o.p. =  out-of-plane; sym. asym. =  asymmetric.svnxmotric andIn assigning tlio hands to various modes of vibration assistance lias boon taken from the assignments of nitrobenzene (Green et al 1961; Stephenson ef al1961), halogenonitrobenzenes (Mooney, 1964) and other disubstituted benzenes (Shurvell et al 1966; Singh et al 1965).o-Z>/ nitrobenzeneAssuming the “NOg” groups to behave as a single particle and lie in the plane of the ring, the molecule o-dinitrobenzene belongs to point group As recom- mondod by the Joint Commission for Sp(udroscopy (Mulliken, 1955), the s-axis is clioson as the two-fold axis (passing through the bond between carbon atoms 1 and 2). The thirty fundamentals then divide among the symmetry species of the group as follows: (I la i4- i0b2) in-plane modes and (5a2+4bi) out of-plane modes. All fundamentals are Raman active and all, except the a>2 vibrations an^  infrared active. Besides these thirty vibrations, there would be 12 internal vi­brations due to two NO2 groups, thus giving 42 vibrations in all.Four C-H stretching modes, two of symmetry a^  and two of symmetry are expected between 3000 and 3100 cm~b Only one frequency, 3098 cm~  ^ is observed in the infrared spectrum of this compound in this region and is arbi­trarily assigned to C-H stretching mode.The infrared peak at 1608 cm~  ^ is assigned to C ~  C stretching modc\ This vibration originates from the degenerate e^ g (1585 cni” )^ vibration of benzene. In o-dichlorobenzene, both components wore assigned to a single peak at 1576 cm""^  (Sclierer and Evans, 1963). Two medium strong infrared peaks, 1456 and 1414 correspond to the 1485 cm"‘ (^ci„) C — C stretching vibration in benzene.The peak, 1041 om'^ observed with medium intensity in the infrared spectrum and weak intensity in the Raman spectrum is assigned to ring breathing mode corresponding to 992 cm~  ^{a^ g) vibration of benzene. Venkateswarlu and Radha- krishnan (1962) have assigned the frequencies 1041, 1052 and 1044 c m i n  o-di- <;hloro-benzene, o-xylene and o-cresol respectively to ring breathing modt».The four infrared frequencies 1293, 1192, 1148 and 1071 cm~  ^ have been as­signed to C-H in-plane bending modes. The corresponding frequencies for o-di- chlorobenzene (Scherer and Evans, 1963) are 1252, 1162, 1140 and 1081 cm~ .^vSimilarly the four C-H out-of-plane bending frequencies are usually found between 700 and 1000 cm~  ^in the vibrational spectra of e-disubstituted benzenes. Thus the frequencies 696, 924, 841 and 789 cm“  ^are assigned to C-H out-of-plane bending modes.Besides these frequencies, the spectrum of o-dinitrobenzene should also con­tain frequencies due to vibrations of the NO2 group. The frequencies 1526 and 1354 cni"^ observed with strong intensities in the infrared spectrum of o-dinitro- benzeno are assigned to the asymmetric and symmetric N =  0  stretching modes respectively. The strong occurrence of these two bands and their assignment(Miss) J. V. Shukla, F .  B. Singh and K . N. Upadhya 5 1 66 1 7 Vibrational Spectra o f Dinitrobenzenesto NOa vibration is supported by tlie assigunnuit of syunnctrieal and asymmetri­cal stretching modes at 1345 and 1,517 cm-^ by StejAenson ct al (1961) and at 1357 and 1650 cm-^ by Green et <il (1961) in nitrobenzene. These two bauds are quite strong, better than idienyle vibration in this region. Tlao (1963) has also marked for the strong occurrence of tliese. vibrations. Tlio throe isomeri<^  fluoro uitrobeuzenes studied by MtHlhi (1964) show strong NOjj vibration. Tlio fnupmmn' J319cm-‘ is assigned to 0-N stretching mode and tin; frequency 864 cm~’ is assigned to NO.j in-plane bending mode.m-T) i tiiirohe nzen eTJio moloculci liolongs to tlu^  saimi point group iis tho o-isomor, but intliis (5taso tho two fold axis passes througli ( arbon atoms 2 and b. TJio tliirty funda- moiitals divide among tho symiuotry species of the grou]> as follows : (lJuid-lOio) ill-plane vibrations and ( 3 « 2 + 6 & i)  out-of-plane u u kIo s . Again, all fundamentals an^  Jlamaii active and all, except the Ujj vibrations are infrared active.The frequency 3099 (un~^  olmerv(Ml v'itli strong intensity in the infrared spec­trum of 7M-dinitrobenzene is assigned to C-H stretc l^iing modt\ The assignment of the C — C stretching modes to tho four fro(piencios 1603, ITdO, 1476 and 1441 cm^i is straight-forward. Tho corresponding frequencies for m-dichlorobenzene (Scherer and Evans, 1963) arc 1580, 1580, 1464 and 1412 cm~h The frequency 1003 cm“  ^ observed with medium intensity in th<^. infrared s])octruiii corresponds to the hand 1005 cm ’ ol)sorved also with medium intensity in tlu^ . Kaman speu - tmui and is assigned to ring breathing mode corresponding to 992 c J i i ' v i b r a -  tio]i of benzene.TJie four C-H in-plane bonding modes are assigmul to the iiifranul bands at 1273, 1172, 1146 and 1067 cu rb  Similarly j)caks at 944, 915, 817 and 791 c m ’ ar<» assigned to C-H out-of-plano bending modes. 'Tliese assigiumiuts are in good agreement with the assignments given for m-difluurobenzeiie (Green H al 1963) and m-diohlorobenzone (Scherer and Evans 1963).Tlie frequencies 1630 and 1357 cm“  ^ observed with very strong intensities in tlu^  infrared spectrum of m-dinitrobenzono are assigned to asymmetric and sym- luotric N =  O stretching mofles rospeotivoly. The freqtiencit^s 1347 and 837 cm-’ arc assigned to C-N stretching and NO^ in-plano bending modes respectively.P'lHnitrohenzeneThe symmetry of this molecule is a)* ^^ -axis passes through the NO  ^groups and tho a;-axis is perpendicular to tho plane of tlie molotuile. Tho 30 normal vibrations belong to the following symmetry species :6(ig 4“ 1  ^“h 4* 563  ^-j~ 2^ 'u 4- 4~ 5621  ^4"Vibrations belonging to the first four species are Raman active and those belong­ing to the last three species are infrared active. The Uu vibrations are inactive in both the spectra.The four C-H stretching frequencies are all expected to lie just over 3000 cm~^  but a precise assignment is difficult, since they tend to mask each other and to interact with summation levels of the C =  C stretching mode (Lebas and Josioii 1956). The strongest Raman line is likely to bo due to the frequency and the strongest infrared band to the b^ u frequency, ainc;e in a crude approximation the. &2m bands should be throe times as strong as the because the C-H bonds mak<i an angle of only 30° with the y-axis but 60° with the s-axis. The frequency 310!) is assigned to ftgw stretching mode.The €2g (1585 cm“ )^ vibration of benzene splits up into and b^ g comjK)- nents when the symmetry i« reduced from to The fnjquenoy 1585 ciu"^is assigned to Uig or b^ g component of 1585 ciu“  ^ 0 — C vibration of benzene. Similarly the (1485 vibration of b(mzono splits up into b^^^ and ftgwponents, when the symmetry is reduced from Z)g/, to As mentioned abovethat the b^ u component is stronger than the component, tlio froquoncios 1478 and 1382 cm~  ^are assigned to the 6^  and b^ u component of (1485 cm” )^ C C vibration of benzone. The benzeiu  ^vibration 1310 ciu“  ^ (^2m) goes to b^ u wlien the symmetry is roduct^d from to D^ fr Th(^  frequency 1282 (;m~^  observed in th(*. Raman s]x>ctrum of this compound is assigruvl to ring breathing mode. These assignments are in good agreement with the assignments given by Stojiljkovic and Whiffen (1958) in the case of p-dihalogenobenzenes.The three C-ll in-plane bending frequencies are charaedcrisod by 135vS, 1161 and 1104 cm“  ^ vibrations of p-dinitrobenzeno. Out of those the frequency 1358 cni"^ is assigned to 63^  species and the, frequencies 1161 and 1104 cni~  ^ to 61,^ and b^ u species respectivcJy.Similarly the four C-H. out-of-plane bending vibrations are not observed in this case. Only tliroe frequencies 906, 800 and 710 cm*”  ^ are observed and arc assigned to this modeThe frequencies 1652 and 1343 cm*“  ^arc assigned to asymmetric and symmetric N =  0  stretching modes. The frequency 1319 cm"^ is assigned to b^ u C-N stretch­ing mode and the frequencies 873 and 839 cm~  ^ observed with strong intensities in the infrared spectrum are assigned to NO2 in-plane bending modes. Tliose as­signments are in agreement with the assignments given by Green et at (1961) and Stephenson et at (1961).A number of combinations and overtones of the above mentioned vibrational frequencies have also been observed and these are included in their respective Tables.(Miss) J. V. Shukla, V. B. Singh and K. N. Upadhpa 618Vibraiional Spectra of DinitrobenzenesA O K N O W L K D O M E N T6 1 9The authors wish to express their thanks to Prof, N. L. Singh and Dr. I. S. Singh for valuable suggestions. One of \i.s (J.V.S.) is grateful to the C.S.I.R., New Delhi, for financial assiatancc.R E F E R E N C E SUruwu, J. F., 1965, J . A m . Chem, 6'oc., 77, 0341.Conduit, C. P., 1959, J . Ghem. Soc.^ 3273.(Ireon, J. H. S., Kynastoii, W. uad LindHry, A. S., 1901, Spcctrochim. AcUi, 17, 480. (Irtsen, J. H. S., Kynastoii, W. ami 1‘tusloy, 11. M., 1903,«/. Chem. >Soc., 173.Ivatritzky, A. R. and Simmons, P,, 1959, J. (Jhem. Soc., 2051.Kross, R. D. and Fassel, V. A., 1950, J. A m . ('hem. Soc., 78, 4225.Landolt BOrnstfiin TabliJ-Zahlonworto uml Kimktiouon, 1 Baiul, Atom utid Molecules,Phtfslk, 1951.l^ obas, J. M. and Josioii, M. L., 1959, Bull. Boc. Chim. F r ., 53, 57, 02.Modhi, K. CV, 1904, Spectrochim. Acta, 20, 075.Mooney, E. F., 1904, S]}ectrochim. Acta, 20, 1021.Mullikon, R. S„ 1955, J . Chem. P h ys„  23, 1907.Pristora, F., HaJik, M., Castolli, A. and Fredericks, W., 1900, Anal. Chem., 82, 495. Rao. C. N K., 1903, Chemical Applications o f Infrared spectroscopy Academio Proas,New York. p,271.Scherer, J. R. and Evans J. C., 1903, S2)cctrochim. Acta, 19, 1739.Singh, V. B., Singh, H. N. and Singh, I. S., 1905, Spectrochim Acta, 22, 927. Stephenson, C. V., Cobiini, *Tr., W. C. am? V\ ilcox, W. S., 1901, Spectrochim Acta, 17, 933. Stojiljko\ if, A. and Whiffen, Tl. if., 1958, Spectrochim Acta, 12, 47.Vonknteswarlii, K. and Radhakrishnan, M., 1902, Spectrochim. 18. 1433.

Vibrational Spectra of the Three Isomeric Dinitrobenzenes

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Vibrational Spectra of the Three Isomeric Dinitrobenzenes

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