Misra, T N

English

IACS Institutional Repository

THE ELECTRONIC SPECTRA OF SOME TRISUBSTl- TUTED BENZENES IN DIFFERENT STATES. IIT. N. MISUAOpTU'S DiCPA llTMKN'r.Indjaj'j' A ssociation fou tiiji; (Ujlttvation of Si if n c f ,(!\IAniTTA-.S2(J{vu'(iu‘(l 12, 1!)(»,;)ABSTRACT. Tlio nc.M ullnivioli't ahsuipHoti spccti.i ol 1 ,2 ,l-liim('tli;\ IlM'tizmc' iind H,1-(IiHjJ()joIo1luuui Imvo l)ccii mvi)''liyLit(ie] m diircJ'i'iil lii Hit* ( .i.sc oi'liiCKH two 1,2,4-triiSiibsliUiiod bou/.oijo.s, tlu-i alJovvcnl iinuisit/ion ih ot (Apr A' —A' .ind I,bo 0,0 biuids up|)Oui htioji^ly ui iJio sj)ocl,ia of Llio hubsluins's lu ibo v.ipoiii Ntuio, liul tbo spoctiiuii ol luuh t)l lb(' compound,s i n  the .solid stiil.o at -  1 SO'T 1 is voiy weak compm od l.o tbo Mjiocdm, duo to Ibt' vupoui and liquid Hl.atos Tbo 0,0 band at' — IS()'’(' ih also di.splai od tovTiid.s bif;b onoi^y icpioii with ro,spoof 1,0 jt.s posjlijon m tbo caso ol ilio liquid II, i.s .siig^oitod I bat tlio obscivcd bmidh m ay loprosont only oiio ol tbo two rompoiiouls into Avliicb tbo baiid.s aio .sjibt up m tbo civsIalH at-is tro .It has boon jiomtod out tliat tbo intoraotjon ol ])ormanont dqioli's ol la'i^bboiiiiripf molo- ciilos on tbo tiaijsitiou momonl, of tbo miloculos in tlio lattice mi^bt l)o pn.ilb  ^ ic.sponsiblo Jor tJjJH laigo .spbtiing1 N T  K  0  I) U C  T  I  O NThe ultraviolet ahsorptioii .spectra ol' .some tri.siih,stitute(l Iiouzimk' com­pounds have recently been inve.stig;ated m tins laboiatory to study the inllueiKiC of intermoleeular fure,e.s on the position and strmtiire of ali.sorjjtion bands in the liipiid and .solid states. Recently, it hits been proposed by Sirkar (J!l(i!:h 0,‘{) that the interaction of permanent electric moments ol the nej^hbourinpj mole­cules on the transition nioment.s of the molecules ui the lattice might be partly responsible for the large .splitting obscrvtMl in tlu' spectra ol some crystals of iiolar molecules at — ISO^ C.Tn a previous communication (JVlisra. 19611) it has been iiointed out that in 1 , 2 , 3-trisubstiLuted benzenes, the transition which is forbidden in frei; molc- eiiles due to cancellation of three migrational moment vectois, becomes allowiid at — 180'’C, but no large sirlittmg of bands could be detected. Since the magne- tude of transition moment is very small in these cases, the interaction with the permanent dipoles of neighbouiing molecules is expecti‘d to be weak. It was therefore, thought worthwhile to extend the investigation to some other jiolar molecules having a large value of transition momimt and 1 , 2 , ‘l-trirnethylbenzcnc and 3, 4-diohlorotoluene were selected for the purpose.32299300 T. N, MisraE X P E R I M E N T A Lcxpoj'imontal ,sot up was the same as dcs(3ribeti in an earlier paper (Misra ]!)()()). (^ lienuciallj^  pure samites of 1, 2, 4-trimcthylbcnzene Jind 3, 4-dichloro- tcdueno suppiu tl by Kastman Kodak Co., and Fisher Seientilic Co., IJ.S.A. respoe- tivcily w(3ie used after fractional and repeated vacuum distillation. For studying the absor ption sxjecti’um of 3, 4-dichlorotolucne in the vajiour state, a 75 cm long absorxition tube provided with (piartz windows and a bulb attached to a side tube for containing the lujuid was used.Thin films of the substau('(‘s of thickiu'ss of the order of a few microns were used to xrroduce bands lu the liquid and solid states. The siicctiograms were taken on Agfa Isoprui films with a Hilger K 1 siiectrograph having a disjiersion of aliout 3A x)oj‘ mm. in the 2000 A region. Microphotometric records were taken with a Kifip and Zonen typo Moll microiihotometor and absorption spectra were calibrated with tlui hell) of a micjophotomctric record of ii'on arc spectrum photo­graphed on each spectrogram as explained in a previous paper (Sii’kar and Misra, 1950).]< E  ,S tJ I. 'I’ S A N D  D ] S LMJ S S I  O NThe microphotometric record>s of the absorption spectia of 1 , 2 , 4-tr)mothyl- benzene and 3, 4-dichloiotoluene aie reproduced in Figs. 1  and 2. The wave numbers of tlie bands with their approximate intonsitiefl and probable assign­ments aie given in Tables I and 11 respectively.(‘0 &(0 )X  ’s10>tDi T .,•  ^ r'' 13f)oOU 3650U 37500 38600 39000p in cm-i1. TMirrophoiometriu rocords of the ultraviolet absorption spectra of 1,:!, 4-trimotliyl benzene in different states.(a) In  the liquid states at 32°C.(b) In  the solid states a t — 180°C.Tht Electronic Spectra of some Trisubstituted Benzenes, etc. 301(a)(IJ)(03ri00() ItOOOO 3 7 000  3 8 0 0 0—> p il l  f in - iF ig . ii. M ioroph otom ol-nc rocoi-dH o f  tlio  u lt iiiv io lo i iibHorpiion Bpecti’u o f H, 4-d irlioroio luon.o  m  rlifforoni stiitos(a) Vnpour Bialc. (b) Ijicpiid slato at 2 2"0  (c) Solid aiate a t  - 1 80°(J.1, 2, 4:~TrirneihylhenzeneThe near ultraviolet ahsorptioii spe(;tiiim of 1 , 2, 4-trinuitliyl henzenc in the vai)()LU‘ Htate was studied by Sreeramamurty (1951). AsBumuif^  the methyl gronj) to behave as a single atom, this moleeule lias the lowest symmetry Cg among the substituted benzenes and the transition in benzene becomesA '—A' transition in this case This transition is an allowed one and the 0,0 band ajipears strongl37 m the spcctium The data hn- the sxiectruin in tlie vapour state awS reiiorted by Sreeramamurty (1051) have been included in tlu' table for comiiarison.In the vapour state, the spectrum of 1, 2, 4-trimethylbenzeiie (iSrecrama- murty, 1951) shows a strong 0,0 bands at 30900 cm“  ^and a large numboi of bands involving dilferent vilnational frequencies. In the liquid state, the compound yields four bioad bands with the positions of maximum absorx>tion at 36185, 3687H, 37385 and 380S5 cm”  ^respectively (Fig. 1, M'able 1) 3 he bands due tothe li(]|uid are broad probably due to thermal motion of molecules and merging of VI— transitions into one another. The aiixiroximate iiosititm of tlui centre of the strong band on the long w^avelength side at 36185 cm'  ^ is taken as the posi­tion of the 0, 0 band. Then it is found that on liipiefaetioii of the vajiour, the 0, 0 baud shifts towards red by 715 om~h The other bands are at distances 693, 1200 and 1900 cm"^ respectively from the 0,0 baud.2302 T. N. MisraWilli tlii^  tJoii(lifi(;alion of the liquid and cooling to — IKO^ ’C, some more Lauds arc oLserved. The strongest Land on the long wavelength side is at 3GI108 cin“  ^ and is taken as the 0 ,0  Land of the system. 1 ’he other liands can then be rejjreseiited liy (‘xoited state vibrational lre(][uenoies 4(U, 091, 890 and 1 2 0 0  cm"^ and their combinations. Some of these freqiumcies agn^e fairly well with the frequencies 711, 927 and 1180 enr  ^ repoitt'd by Sreeramamiirty for the vajinur state-. The frequency 641 em~^  observed in the spectrum of the crystalsl^ABLE rLlltiaviolet absoiqition bands of 1 , 2, 4-trimethylbcnzene in different statesVapour(iSI'ooraiiiamiiil>y, J 9o 1) Liquid a t :12"(' 8(ilul at -  180"OWavo numf>i‘j aiulliit.ousiiyAHMigum 'litAVavo m ijnlii'i' (cm -i) and IntcuiHityAswigiimmitWiivn nuiiibcr (e j n - ' ) and 1 nil'll,sityAKhJgiiinontH5977 (vw) 0 -  !>2;iHG:1u1 ( vw ) 0 - 5 4 0 ':{Goh;} (vmO 0 - 2 1 7:iG'jou (vh) 0.0 30185 (s) 0,0 3G30S (VK) 0,037UJ5 (in) 0 1 J 15 30824 (w) 0 +  4G1.37G11 (h) 0 1711 3GH78 (s) 0 1 GO 3 37059 (h) O-l-GOl:J7S27 (lub) 0 ! 027 37385 (s) 0 [ 1200 37258 (m) 0 1-80038080 (jiiw) OH 118038085 (m) 0 1 G03 ) 1200375G8 (h) 0 1 12003818G (luw) 0 ) 128G 38i2G8 (in) O -hGOJ -h 120038760 (w) 0 -1 -2 x 1 2 0 0at ~180°C was not observed by him in the case of the vapour, but it may be noted that Kohlrausch and Poiigratz (Magat, 1936) reported two strong Raman lines 557 ein~^  and 474 cm~‘. It is seen that when the vapour is liquefied the band system shifts towards red by 715 cm~^  and on solidificiation and subsequent cooling to — 180“C, tlio band system shifts towards shorter wavelength by 183 cm"^. Rurther, the integrated absorption at each band becomes much smaller when the liquid is frozen and cooled to — 180“C.This decrease in the strength of absorption may be explained by assuming that this band system constitutes one of the two components in which the original band system is split up in the crystal at — 180“C and that the other component may be on the short wavelength side. As the crystal structure of4;he compoundat — 180“C is not known it has not liecn possible to ealcnlate the exact positions of the split components,3, 4:-Di('MorotolueneAs explained above this molecule also has the symmetry C„ and tln^  migra- tional moment vectors add to give a large value. J^'lie transition is allowed and the 0,0 band is exjiected to appe.ir strongly in the spectrum oi'free molecules,Spectru7ii in  Ihc vapou r phase..Three gronjis of bands degraded towards red, consisting of about fifteen pro­minent hands (Fig. 2 a) have been observed. The veiy strong sharp band at 3r>53S cin“  ^ on tlie long wavelength side has been taken as the^  0,0 band of the system. All the other bands can then be assigned in terms of ground state fre- (|uencies 303 and 430 cm^^  and upper state fundamentals 232, 300, 598, 799, 995, and 1170 their combinations.TABhF IJUltraviolet absorption bands of 3, 4-dichlorotohiene in different statesThe Electronic Spectra of some Trisuhstituted Benzenes, etc. 303A'lipom al. :i2 ''r  Oiiili len g th  7r> cm l,u|u](l lit Solid  a t  -  J80-'CnnuiOcr A\5ivc mimbi'i' AVavi' miml)t*r(em 't) H,nd As.signm '111 (cja~ i) iind AHHignm 'lit (cm -J) and AnsignnwntIntensity Tnti'iisdy Intensity30102 (w) 0 136351 75 (w) 0 -  36335.53S (v,s) 0,(^ 35300 (vh) 0,0 35.551 (v.s) 0,035770 (w) 0 1 232 36292 (vh) 0 1 992 36123 (m) 0 1 57235934 (w) 0 1 396 37284 (m) 0 12V  992 36347 (w) 0 i 7063(1135 (m) 0 1 598 36540 (h) 0 1 995:i(.317 (m) 0 1 779 :i693() (w ) 0-1 572 1 7960 1 2 x 3 9 637302 (m) 0 (-995 1-30533 (vh) 0 1 995 79630718 (ms) 0 1 117037554 (m) 0-1 2 x 9 9 536925 (m)U 1-995-13900 1 598 t-77937163 (ms) 0 !  IC25371129 (a) 37767 (ms)OH 1)9.7 f- 59S0H-2X99.7 0 1-2x99.5 H-232304 T. N. MisraTho Raman and nifrared spectra of the molccmle have recently been ropor- t(id by ])eb ajid Ranerjee (U)b0 ). The two ^^ round state fundainenetals and 43b cm~^  observed as v—>o tTansition in the present investigation agrees with the Hainan frequejunes 368 and 435 cm“i reported by tliern. 'fhe upper state fundamentals 396, 598, 779, 995 and 1170 cm“i satisfactorily correspond to the Raman and uifrared fieipiencies 435, 686 , 805, J030 and 131J cin~^  reported by Dob and Ranerjee (J960)Tn tlie liquid state, the substance gives a spectrum consisting of thcrco broad bauds. The centres of the first band at 35300 cm~^  is taken as the jiosition of the 0 , 0 liand and other bands arc s(‘parated from it by 993 cni“  ^ and 3 x 993 em . Tims on liquefaction of the vapour th(‘ hand system is shifted tov'ards red by 338 cjii 'kIn the solid state at -  180“C, the ahsorxitioii si>eetrum of the substance consists ol about seven prominent but weak bands. The 6 v,st band at 35551 cm  ^ is evidently the. 0 , 0 band of the syst(‘in. The otlier hamls can then bo oxxilained m terms of iixijiei state fundamentals 573, 796 and 995 Lm~^ . Thus on solidilieatioii of the vaxiour and its subsequent cooling to — IHO'^ 'd, the band system is observed to shift slightly towards highei energies and also the strength of absoiption dimiiiisJios apjireeiahly. ,This decrease in the strength of absorption in the crystals at - I80“C may be exjilaiiied in the same way as in th(‘ jirevious case, i t  may be noted here tliat similar shift of one of the s i^lit components to the other region of the spec­trum has also been olisei ved by Rornstein in the case of broniobenzene as rejioi'ted by Kasha and Oxjxienheimer (1963).A N () W  L K D U M K N 1^’The author is grateful to Prof. S. P. Sirkar. D.Si;., F .N .l , for his kind in­terest and guidance in the work.R  E  F  IC R 10 N O E SDeb. T\ K , niid R an erjee. S R , 19(i0., Tnd Jou r Ph ys , 34 , n/)4.Kuslm M., Uiurl ()ppe.i\lioijn''r, M , 19C2 , "I'liooiy o f meleoviJar ExoitoiiH., Mo Drew H ill hook (lojnpm iy , ]i IIMIMagni J\l., I9.3fi TSTumerjcal D a ta  on itiim an E f fe c t ,  p 72.M isra T  N., l% 0,7v(fZ  ,/om T//?/*■., 34, .'IS 1.Misra, 'P. Nk inCIJ , Ind,, Jour. Phya. 37 , 17H.fiiikai S C , and M isra T. N., 1959 , Jn d  Jo u r Phys . 33, 4.5.S u k ar M. C ,  1992. Prue. Na|,l Jnsi ,SV;/ of In dm. 2 7 J .  608.Sirkar, S. 0 . ,  lOO.'l In d  Jour. PhyA., S7, 101.Sroeram am urty, K .,  1951,, Proc. J^atl. Inst, of Sci. of In d ia , 17, 385,

The Electronic Spectra of some Trisubstituted Benzenes in Different States. II

ISTHE ELECTRONIC SPECTRA OF SOME TRISUBSTITUTED BENZENES IN DIFFERENT STATES-1*T. N. MISBAOi'TIOS DfiPARTMliNT, INJJTAN AbBOOJATION KOJl 'J.MIK ('l3i;i'lVAT]ON Olrt'tSLlENri'jC a l c u t t a -;] a[Rmew&d Jcuiuaty 7, lilO;])ABSTRACT. Tlui ]i()nr ultmvioli'i abKoipFmu Hpuctm of I, 2, .‘l-lndiloio- imcL J, 2, ,‘{- tnJiyrli’oxybonzi'no liavo boon HiudioLl in t.lio liquid kIiIpIo, hoIkI siaio u(i room li'iiiporaturo mid at — I8U°C and uIho in rigid gla.H« iiiodia in alouJiol at t]io HiIiiim toiiqioiaUiro In tlio liquid .stato and m  tlio solid stato at room l ompmatui o liotli llio siibHtanoi'.s yiold weak, broad, ddfuso bandy flUuwing tlio oluuatmstioH ol foi'biddou tiMiihiiion as in fio(‘ moloouloH duo to onnodln- tion of throo migration moniont voolois A t --1 8 () '( !, tlio transition boooinos allowod and tlio band syHtoins ooiiHiHts of .«lmip bands with tlio 0, 0 bund at llTiD lT o iiri foi J, 2, 3-tric‘liloro- bonzoiio and at IJOIOIJ om -i lor 1, 2, 3-tiiliydioxybouzon,o. Tho ollior Inind'' aio Halisfaotoj'ijy aH.signud to oxoitod stato vibrational Iroipionoios Tlio slruoluro ol tlio bands in tlio rigid gla,sH at — 180°C is similar to that of puru orystuls ut aaiiiri tomporaturo oxoopt that it is nt liighor onorgy region and in 1, 2, 3-trihydroxybcuisr,ono tlio bunds ai'o sliaipor.Those reaiilts indicate that a portui’bation on the energy states ot tla^se moiocules oecnr a t — 180°C. I t  Iuxh boon pointed out that tlio inteiactioii ol ]jermanont dipoles of tho neighbouring luolueule.s on tlio transition moment d  the moleeules m Uie lattice might play a doniiniint role in detorimning tlie cnorgy siutoH ol iiioleeular crystalsI N T  K 0  D U (J T  I O NThe inteiiHiiy of absorption and strueliii'o of hands in the electronic spec, tiu of trisubstitntod benzenes are knowji to dejn'iirl on tlie .symmetry of tlie mole­cules. In symmetrical trisubstituted benzenes the 0,0 band in tho near ultravio­let iib.sorption .spectra is forbidden in tlie vaponi’ stale as in benzene, wherca,s in tho spectra of 1, 2, 4-trisiih.stituted benzenes the 0,0 hand js  allovyed (iSponer, 1047). iSklar (J942) calculated the contribution.s from the sub.stitiients to the migrational transition moment and found that tliey annul one anothej' in the first order in J , 2, ll-trisubstitiitcd benzenes, vyhen tho snbstitucnts at the i)ositions are the same. Tims theoretically, the spectra should appear in these oases only through yibrational moments i.c. by distorting the .symmetry of the molecule through excitation of vibrations Tu 1, 2,  4-tri.substituted benzene, however, the three migration moment veotor.s are added up to give a large re.sultant migration moment and the spectra are exjunited to be allowed with a strong 0,0 band. The influence of interraoleoular field on the electronic spectra of a few trisubstituted benzene has recently been studied by a number of workers. It has been observed*C□mlnul^loatl)d by ib'ol. fcj C Sirkm’.m174 T. N, Misrathat the Hymmctrically forbidden iransitiouH in 1,3,5-trichlorobonzene (Banerjee; lOf'jT) and l,,‘b'^ -tA’i™cthylbenzcne (Sen, 1959) become allowed in xmro crystals when cooled to-180°C. Schneiip (1950) studied the polarised electronic spectia of orientated single crystal of 1,3,5-trichkirobenzene at -180°C and oonclnded that the ai i^jeai'ciicc of the 0,0 band was due to change in symmetry of the mole­cule. Roy (1958) observed that in the spectrum of the substance disi)ersed in rigid glass media at -180°0 also, the 0,0 band was present. Tn the jiresent work, investigation,i^ on the electronic siiectra of trisubstituted benzenes in different states have been extended to the rnolccnles of l,2,;i-trichlorobenzene and 1,2,3- trihydroxy benzene.K X P E i l  1 iM N T  A 1jThe experimental set ni) was the same as described iii an earlier paper (Misra, 1960). Chemically pure 1,2,3-trichloro-and trihydroxybenzene sniijilied by Dr. Theodor Schnehardt of Munich and R. Merck c'k Cki rosi>cctively were repeatedly crystallised from solutions in alcohol and the crystals were further purified by vaituiim sublimation before use.Thin films of the substances of thicknesses of the order of a few microns were required to produce bands in the solid state. To study the absiirption siiectra, in the liijuid state, the thin him of substances enclosed between two quartz plates was ijlaced in a heating chamber which was kept at temi>eratiires about 5"'C above the resjiective molting iioints of the substances.The solvent used to study the absorption siiectra of the substances in solution and in rigid glass media at -ISO'^ C was ethyl alcohol. The solvent was found to produce no absorption band in the region under eonsideration. A brass cell of thiokness 1 cm provided with (piartz windows was used to study the absoip- tion spectra of the substanee in solution and in rigid glass and the strength of the solution was .01 % by weight in each case.Speetrograms were taken on Agfa Tsopan films backed by a metal sheet with a Hilgor R 1 spectrograph giving a dispersion of the order cf 3 A per mm. ill the region of 2000 A. Iron are .spectrum was photographed on each spectro­gram as a comparison. Microphotometric records wore taken wuth a Kipp and Zonen self-recording microphotomciter. The absoriition spectra were calibrated with the help of mierophotometric records of iron are lines using the method described in an earlier paper (Sirkar and Misra, 1959).H E S U n T S A N D  J) 1 S 0  U 8 S 1 O NThe microphotometric records of the absorption spectra of the 1,2,3, -trichlorobcnzone and 1,2,3-trihydroxybenzene are given in Figs. 1— 4 and the positions of the bands in wave numbers, their visual strengths of absorption and probable assignments are given in Tables 1-111.The results have been disoussed in thcj following sections.\,2,’^ -TriMor6benzeif\cThe near ultraviolet absorption spectra of 1,2,11-ti’iehlorobenzeiic along with those for l,Il,d- and 1,2,4-trichlorobeuzene were studied by Conrad- Billroth (1932) in hexajie solution and several distinct maxima were observed. Though the absorption is strong in thc! eise of I 2. 4-trichlorobenzone, the other two compounds exhibit very feeble absorption. This shows the (diaraoteristics of foi'bidden transition. The absorption spectrum of 1, 2, 3-triehlorobenzene in the vajiour phase was studied by Miioner (1947) who observed that the structure of the spectrum was dilTeront from that ol tlui other two isomers. It consists of three broad, diffuse and weak bands which are sepaiated from each other by about 995 cm“'. No band due to 1-->0 transition in the vapour phase was ob­served and therefore it was suggesti'd that the 0,0 band might be jireseiit in the first weak group. The centre of the lirst group is at about 35910 cm“\ but as the transition is ordinarily forbidden, the 0,0 band cannot be strong and therefore it cannot be at the centre of the first band. It has been observed in the present investigation tliat in the Inpiid state at 70“C also 1, 2, 3-tri(ihlorobenzene shows thiee bi-oad bands (Fig. I, Table i), the centre of the bands being at 35535 cm-', 3()G07 cm  ^ and 37681 cm respectively the difference between successive baudsThe Electronic Spectra of some Trisubstituted Benzenes, etc. 17635000 36000 37000 38000 39000V in cjiii-i —>Pig , 1. M icro photonic trio records of the uHmviolot absorption spoctra of l,2 ,3 -li icliloro benzene m different atatc.s,(a) liquid state  at 70*^0. (b) solid state  a t 32“C. ^c) solid s ta te  a t —180*’C*176 T. N. MisraTABLE] IUltraviolet absorption bands of 1, 2, 3-trichlorobonzeno m different statesLiquid  ftt 70°C Solid a t 32“C Crystal a t — 180°CW ave No. in  om~i LifforoncuW ave No. in  ciii-i DifforencoWavo No.in  cin~i AHSignmerit35535 ( v h ) 35638 (h) 35347 ( i i i H )  0,01072 107535610 (w) 0 +  26930607 (h) 36713 (a)1072 1075 35733 ( v h )  0 +  38037081 (8) 37773 (H) 35837 (w 0-1-4903G002 (vw) 0-(-20!» I-3S6 300G7 (niH) 0 [-269 |-^90 0-1-720:K;22H (w ) 0 1 380 I 49030339 (111) 0 I 99230439 (111) 0 I J09230507 (vw; 0-| -i2 l030725 (iiiw) 0 1-992 1 380 0-1-1092-1-20930825 (vb) 0-1-14780 1-1092 1-380 '30929 (w) 0 -f-1092-^49037059 (n w ) 0-H720-|-992 37159 (111) 0-1-720-1-109237316 (ill) 0 I 1092-1-490-1-386 0-1-1478-1-490 0 1 -2 x 9 9 237431 (111) 0 199 2 -1 1 0 9 237531 (imv) 0 | 2 X 1092 37049 (w) 0 1-1092-1121037717 (w) 0 1 2 X 9 9 2  138037817 (111) 0 1 2 x  1092-^2090-1 1092-1 992-1-38638033 (w) 0 +  2x 1 0 9 2 -1 -4 9 00-1-1478 +  1211)38151 (w) 0 I 1092 +  9 9 2 + 7 2 038251 (vw) 0 1 2 X 1 0 9 2  1-72038413(a) 0 +  2 x 1 0 9 2  1-386-1 4900 +  1478 +  1092-1-49038523 (w) 0 +  2 x 1 0 9 2  +  99238809 (111) 0 -1 -2x992-1-14780 +  2 x 9 9 2 -1 -1 0 9 2  +39009 (1118) 0 -1-2x1092-1-1478 39499 (m) 0 +  2 x 9 9 2 + 2 + 1 0 9 2being about 1072 cm~ .^ Thus it appears that on liquefaetion of the vapour, the band system is shifted by about S75 om'^ towards red.When the liquid is solidiliod at the loom teinxjeraturc the bands become a little sharj)er but no further resolution of the structure of the bands takes place and the spectrum consists ol three broad bands as in the liquid state, the ceiiti‘es of the bands being now at 35038 cm-^ 30713 cm~  ^ and 37773 cm“i respectively. Thus the band s^ s^tem is shifted by about 272 (im“  ^ towards red from its position in the vaxiour iihaso.When the temx>eriiturc of tlie crystals is lowered to — 180"(J each of the three bands is split up into a number of bands and the HXJeotrum consists of strong shaiq) bauds as in the casc‘ of allowed transition. Tlui very strong band at 35733 ciu“  ^ was axixiroximately at the centre ol a numbei’ of bands. The first band on the long wavelength side at 353‘47 crn i was taken as tlu‘ 0, U band of the system. All the other bands in the spectrum could then be exjilaincd satisfactorily m terms of excited state Irequencies 2(i9, 386, 490, 992, 1092, 1210 and 1478 cm“  ^and their combinations. These frecjuencjes correspond lesiiectively to the ground state Kamaii frequencies 333, 486, 505, 1076, 1151, 1248 and 1554 cm“' as given m Landolt-Bornstein’s Tables (1951). No ilamaii-shift of 720 cin~^  was givenThe Hlectronic Spectra of some Trisubstituted Benzenes, etc. 17'?TABLE XIUltraviolet absorxition bands of 1, 2,  in alcohol3-trichlorobcnzonel a  solution uL Tu rigid gliiBK m edia at — IS0''CW ave No. VV^ avti No.la  om~i Oilforcaco la  ( iia 'i AHHigninoat36463 («) 0, 0.36710 (w) 0 +  250301352 (s)1050 35844 (VH) 0 4  381.30702 (VHJ105035947 (w) 0 + 4 8 430107 (iuh) 0 +  260-1-48437753 (8)305.38 (ms)0 + 7 3 4  0 +  107530903 (v8) 0 + 1 4 4 037177 (ni) 0 4  2 5 0 + 3 8 1  +  107537281 (m) 0 +  734 +  1075. .37380 (111) 0 +  484 +  U 4 037870 (in) 0 +  2 x 1 0 7 5 -^ 2 5 037997 (ms) 0 + 2  X 1075 +  381 0-1 1 4 4 0 + 1 0 7 538479 (ins) 0-H2X 1075 +  381 4-484 04^144041075-1-48439043 (him) 0-1-2-1-1076-1-1440178 T. N, Misrain Landolt-Bonistein’H Tables but such a frequency is usually observed in other 1, 2, S-trisubsUtutod benzenes such as trimethylbenzene, trihydroxy benzene (Landolt-Bornstein’s Table, 1951). Thus the very strong band at 35733 cm"  ^which is at a distance of 386 cm~  ^ from the 0,0 band represents the centre of the broad band observed in the spectrum due to the (srystal at room tempera­ture. Hence the 0, 0 band is on the long wavelength side of the centre of the first broad band observed in the case of the litiuid and it has been con­cluded that the 0, 0 baud appears only when the crystals are cooled to — 180°C.When the substance is dissolved in alcohol, three broad bands, as those due to the liquid state and solid state at 32“0, arc observed, the centres of the bands being at 35052 c m " 36702 cm-  ^ and 37753 cm-^ respectively (Fig. 2 Table II). fn hexane solution (Conrad-Billroth, 1932) the 6rst broad band was approxi­mately at 35700 cm' Thus in alcohol solution at room temperature, the band system is shifted towards red from its position in hexane solution and it is axiproxi- mately m the same jiosition as in jnirc the spectum of crystals at tlie room tem­perature.3800U 3900035000 36000 37000V in cm~i —fF ig . 2. Mici-ophotouioii'ic lecorda of tho uU iaviolct ubsorplion apectm of l,2,3-tm !lilorobenzent).(a) alcohol solution a t 32°C. (b) K igid  Glass Medium at --180"U .The assignments of the-bands due to crystals at — 180®C are supported by the spectra of the substance dispersed in rigid glass medium in alcohol at —180°0. The structure of the bands in rigid glass is similar to that due to pure crystals at — 180‘^ C. The first band of medium strength is now at 35463 cm=^  and taking this as the 0, 0 band, the other bands can bo assigned to upper state fundamentals 256, 381, 484, 734, 1075 and 1440 .cm-^ and their combinations. Thus the 0, 0 baud of 1, 2, 3-tricldorobenzene in frozen alcohol at — 180°0 is at a distance of 116 cm'^ on th^ high energy side of the 0, 0  band due to the pure crystals at — 180°0 and the uiiper state fundamentals in the two cases agree fairly well with each other.Thus it is seen that in the si)eotra of the substance in rigid glass media at — 180“0  and also of the pure crystals at — 180“C> the strength of absorption is muck larger than that in free molecules and the broad bands of crystals at room temperature are resolved into a number of sharp bands in the former case. Tn rigid glass, the bands are less sharp tlian in pure crystals at — 180°0 but the struc­ture of the spectrum is the same in both the cases. These results indicate that transition which is forbidden in free molecules due to cancellation of three migj’a- tional moment vectors, becomes allowed probably due to some distortion in the symmetry of the molec-ules at — 180“C. The weak 0. 0 band in the spectrum due to the crystals at — 180T  indicate that though the transition is allowed at this temperature, the magnitude of the transition moment is very small and its interaction with the jiermaneiit dipole of the neighbouring molecule is expected to be very weak. It has been proposed by Sirkar (1902, 19011) that such interac­tion might be partly responsible for producing largo splitting of electronic bands in crystals of polar molecules. Tn the present case, the interaction may be too weak to iiroduce any detectable sjiUtting of thc^  bands and actunlly no splitting has been observed.The Electronic Spectra of some Trisuhstituted Benzenes, etc. 1791,2, ^ .Trihydroxyhenzenelittle  work has been done on the electronic spectra of pyrogallol in the near ultraviolet region. Leonard -liird (1957) observed the absorption maximum of the substance at 2670 A in solution in alcohol at room temiierature. Shergina ei. cd. (1959)al so reported similar observations. In the present investigation, the ultraviolet absorption spectra of the substance wei e investigated in the liquid and solid states at room temperature and also at — 180°O. The spectrum of the suhatance in solution in aloohal at —180°C was also photographed in order to verify the assignments of the hands due to the polyorystallinc mass at —180"0.In the Liquid state, a broad region of absorjilion estending from 35627 cm"^ to 38156 cm~’ was observed without any discrete structure. When the liipud was solidified at the room temperature, three broad bands were observed, the centres of the bands being at 35999 cm~ ,^ 36678 cm"  ^ and 37246 cm”' res­pectively.When the solid is cooled down to —180°C, the spectrum consists of strong but broad bands and eight strong hands are clearly resolved. No other bands were observed on the long wavelength side of the strong hand at 36109 cm"' and this was taken as the 0, 0 band of the sj^stem then the other bands represented and this was taken as the 0, 0 hand of the system then the other bands represented excited state frequencies 429, 537, 675, 972,1237 and 1463 cm-^ which correspond to the Baman frequencies 406, 573, 767, 1015, 1237 and 1473 cm”' (Landolt- Bomstein’s Tables 1951). A strong Raman line 1386 cm”'  has been reported in these Tables and the band due to the corresponding upper state frequency is180 T, N. Misraprobably not resolved from the two biinda representing the frequencies 1237 and 14d3 om“h35500 30500 37500 38500V m om~iF ig , 3. Mici'ophotoiiuiino records of tho ulivuvioloi abfior]itinn syjof-lva of 1,2,3-tfiliydroxyb(’nzf)ni‘ in diffoiviit sfcateH.(a) liquid n H 4()'’r  (b) Solid n.i 3 2 (o) solid nl - 1 8 0 “C.TABLE TITUltraviolet absorption bands of pyi*ogallolLiquid  a l 140“C!SoIkI a troom tompombnro Solid at - I80^rKogid glass a t - IK0°(!) m alcoholW ave No. in i‘iu“ i AHnignmontW ave No, m  cm~i AHRignmi'iilWave No, in  cm“ i . AHsigieiumt35!)!)9 (m) 0,0 36109 (vs) 0,0 35857 (s) 0,0Broad absorption 36538 (rn) 0 1 429 30273 (me) 0 +  416region 36678 (s) 0-1-67036646 (ni) 0-1-537 36392 (m) 0-1-535extending from 37246 (h) 0 + 1 2 4 736784 (vs) 0-1 675 36526 (ms) 0 +  66935627 cm~i 37081 (w) 0 +  972 37081 (s) 0 + 1 2 2 4to  38156 c in -i 37346 (s) 0-1-1237 .37274 (h) O f  142737572 (s) 0 + 1 4 6 3In the case of the solution in alcohol at —180°0, the structure of the spectrum resembles that due to pure crystals at -  ISO^ U except that in the latter case the bands are strong but quite broad while in the former case the bands are sharp. The first band on the long wavelength side assigned as the <1, 0 band is pure crystals of 1, 2, 3-trihy(]ro\ybenzeno at - -180“C is quite strong compared to that in I, 2, 8-trichlorobenzene. and tlie transition moment has a larger value in the former tlian in the latter molecule. The broadness of the bands probably indicates that the bands are split uji in the spectrum due to pure crystals at --IHO‘^ 0 and the split components are not resolved. The 0, 0 band in this case is at 35857 cm~^  and the other bands represent upper state fundamentalsThe Electronic Spectra of som,e Trisuhstituted Benzenes, etc. iS l35600 36500 37500 38500V in mn~i-4Fi^- 4. Miorophotomeino rooordH of ultraviolet ab,sorj>tion Hpeotmm ol“1,2,3-( nhydroxy bonsseno in rigid glass medium at41fi, 535, 609, 1224 and 1427 cm~^  which agree fairly well with tlio values lu the case of tlie inire crystals at -  180°0. Thus the 0, 0 baud ni pure crystals at —180*^ 0 is shifted towards the higher energy region by about 252 cm"  ^ with respect to that duo to rigid glass medium at the same temperature.These results indicate that the symmetry of the molecule is disiriibed at low temperature and the transition which is forbidden in the free molecule is made allowed as in the case of 1, 2, 3-trichlorobonzene. Further interaction of permanent dipoles of the neighbouring molecules on the transition moment of the molecules in the lattice plays a dominant role in determining tlie cnojgy states of molecular crystals.A C K N O W L E D G M E N TThe author is grateful to Professor S. Cl. Sirkar, D.8c,, F.N.I. for his kind interest and guidance in the work.R E F E H E N 0 E HRancrjee, 8. R ., 1957, Ind. J .  Phys.. 31, 483.Conrad.Rillrotli, H „ 1932, Z  f. Phya. (Jhf.m,, B19. 70.Jurd , L ., 1957, J ,  Am. Chem. Soo„ 78, 3445.Laridolt and Bom slcin, 1951, ZahlmweHe und Fwiktonen I  Baud, Teil 2, p. 523 and p.408182 N . M israM iara , T . N ., 1 0 00 , ln.d. J. 3 4 , 3 81 .K o y , K. B . ,  1907 , Ind . J. Phya., 8 1 , 0 8 8 . fcJohoepp, O . P . ,  1 0 0 9 , J. Ohem. Phy^., 30« 8 6 3 .Son , 8 .  K . ,  1 9 0 9 . Ind . J. Phys., S 3 , 4 1 .Slio j'g m o, N , I . ,  et al., 1 9 5 9 , f lu a  lUsHcJt Hsnch Pu-o,, 2 5 , 2 3 0 . S ii’lcu.1’, S . n .,  rt,nd Mifam, T . N ., 1 9 5 9 , Ind . J. Phy^^.t S3 , 45 . S irk iii’, S . C , 1962, Proc-. Nat. Inat Sci. of India^^ 27>4, 5 6 8 . S irk a r , S . C ., 1963 , Tttd. J. Phys , 37- 101 ,S k la r , A . L ., 1 9 4 2 , PejV. M.od. Phys., 4 1 , 2 8 1 .S p o n er, H , , 1 9 4 7 , (yhem-, /Jew., 4 1 , 2 8 1 .