Bishui, B M

English

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a8 THE RAMAN SPECTRA .OF 1, 2 .. AND I, 1-DICHLORO-ETHANES IN THE SOLID STATE '"' Bv B. M. BISH"£1t (Received for p I(blicatiotl, Plate XII ABSTRICT. 'I'he Raman spedra of I. 1- dichlur ant! and 1, 2- dichloroethalle ill ~he :;olid and liquid states have been studierl in order to est the h.lpothellis put forward by previoull autbors rp.garding the <'ooexistence at ro ional isomer" in the case of 1·2 dichlo(oethane in the liquid "tate, It is obst>rved tlta both the EubstAnces y1eld ten Raman lines having frequency shifts below 1 IOU ettl' I in th iquiq state. &.me of these lines of I, 2-dichloroethane disappear when the lIubstauce s ,\:.;iifi('d, but ill the case of 1,1-dichlot'oethane all these lines persist itl the solid stat IJ. is pointed ont that these results do lIot support the h} pothesis that the extra Ramab 1 II in the liquid Atate are due to the ('()·exi"tence of rotational i~omerl\ It i& puiutc'd out lb', the results can be explaine(1 Oil the as'lulllptil)u that strongly n~socintcd n1t)lecnle~ a'e pr('~(' ill thebe tW(lIi'lltid~ INTROU{JC'l'ItiN The Ralllan sll~ctra of ethylene dihalidcs ill the solid state \\ere first StllJ.CU by Mizushima ct al (1936, 1938). They observl'd that some important Hnes disappear in th.: solid stale and explaiucll the phenomenon 011 the hypoth~::.is that ill the so:id states the molecules are ali in the trailS state, while the liquid st'lte contains lhe molecull!s of both the trans aDd gaucbe O!' cis configurations. L'ltcr, Sirkar and Bishui !r94S) ~tudied tlle RanJan spectra of ethylene dihrol11id:: in the liquid and the solid state Hllrl also the polarisation of the lines due to the liql1;d I:>taie at room tCll1peratUle, and critid::.ed tbe hypothesis put forward by Mizushima ei al showing that the two lines 10S6 cm-1 and 1441 cm-I of liquid ethyiene dibromide were tota.lIy depoIarised, although according to their hypothesis these linc,; ought to have been polarised. An altern~tive hypothesis that in the liquid state some of the molecules migbt be in a strollgly associated state, forming thereby groups having the symmetry C:IV and that in the solid state lbe group might change to one having a symmetry D3h was put forward by Sirkar and Bilihui (1945)' Further, the results of investigations of the Raman S]Jt!ct1'8 of ethylene dibromide dissolved in different solvents by Bishui and Sallyal (1947), of their polarisation and of the ratio of the -intensities of thtl lines 551 cm- I and 660 cm-1 of the pure ethylene dibrol11ide at different temperatUl'es by the present author (1948) seemed to support the view put forward by Sirkar and Bishui (1945). The sure test of the different hypothese!', however, lay in the study of the Raman spectra of dihalogen ethanes in ,which there can be no rotational IICommUDicated by Prof. S.C. Sirkar , , , , 320 B. M. Bishui " isomers. By comparing the Raman spectra of such disubstituted etbaues with those of similar molecules which may have rotational isomers. one can denllitely say whether the presence of rotational isomers is responsible for the presence of too many lines in th~ Raman spectra of these substances. For this purpose, the Raman spectra of I, 2-dichloroethane and I, I-dichloroethane in the liquid and the solid state have been studied in the present. investigation and the results which arc described below lead to the dennite conclusion that the extra lines present in the Raman spectra of these substances in the liquid state are not due to the presence of totational isomers. ~XPE,RIMENTAL 'the apparatus used III the present invc!ltigatioll for the study of the Raman spcc.tra of the !>ub~tances ill the solid ~:ate at low temperatures was • the same as that described, curlier by Sirkar aud Biflhui (I943). Kahlbaul11 '5 pUl'e substallces distilled in vacum '" ere put ill a double walled cylindrical pyrex glass tube held in a vertical positioll 10 the: liquid oxygen contained in a transparent De\\ar vessel. The intt:l'space belweell thl:! two walls of the container was evacuated with a Cellco hyvac pump, so that 011 pouring the liquid oxy~en into the Dewar ve:;scl to fill it up to a certain height froln the bottom of the containcr, the temperature of the liquid was lowered very slowly. and consequently the process of !>olidification also was very slow. ~l1e frozen mass thus produced was transparent. The: dry air \\ as introduced afterwards into the interspace mentioned above and the temperature of the solid reached a steady value of about-170°C within an hour. A Fuess glass spectrograph having a dispersion of about r4 A. U. per mlll. in the region, 4046A was used. The liqUId was illuminated by light flOm two • vertical mercury arcs condensed by two six inch glass condensers placed Oll the opposite sides of the container. Cobalt· glass filters were placed in the path of the incident light to cut off continuous background in the blue-green region of the spectrum. The polarisation of the Raman lines was studied gualitatively by photo-graphing the horizontal and vertical components of the scattered light sil11ultaneously on the same plate with the help of a double image prism as usual. The liquid was contained in a horizontal Wood's tube provided with .a plane window. Light from a tnercul'Y arc focussed with the help of a condenser was used as the tncident light in this case also. In the ca~e of totally depolarised lines the horizontal ('omponent was more intcm.e than the vertical component in this arrangement. RESULTS AND DISCUSSION .. The spectrograms obtained for the liquid and solid states are reprOduced in l'Jate XU. nSHUI PLATE XII h.J.2 I kl 4 Ramdn Spcctrd f'lq I, 2 - DIChlOl tl0thdnp dt al ( Ilt + ~r) , ' FIQ 2 I, 2- l7UC hq 3 1 1 - DlchloroethClnp cd about + 30'C Fig 4. 1, 1 - 170'C -Rtiman Spectra oj I, l .. and I. I-Dichloroetht"le, 321 Ttle results are given m Tables 1 and II. The &ecoud column of eacp table contaIns the results reported by some of the previous workers. The letters P and D denote polarised and totally depolarised (p=6/7) respectively. '['he approxittlal~ visually estimated intensIties are gIVen in the pnrentlicses. The data for the solid obtained in the present investigation are given in the last column. TABU! I, 2-dicbloroetbaue elCH CHaCI. ~iqllid State Solid ~tate --- ------Present author. Mizulobima et til 1di7:u'Ih IPa et til (1938) Present author (1938). at a J>ut-I4°"C_ at about-170·C. --- ----I - 53, k:!: 58 (2b)_ k I - I - 74, k± 80l (I). k 128 (3ble, k, n 12,5 (sb)e±. k± V -265 !2)e, k; P 265 (s)e±, k, i V ~ 264 (2)e, k 301 (6'e, k ; P 300 (8)e±. k. i 3u 3 (5)~, k 300 (~)e, k 409 (2)e, k; D 0111 (5)e±, k, i V -654 (S)e, k ; P 654 (8)e±,k,i.f V V 676 (,s)e, k ; 0 677 «('b)et. k: i V -754 (Iob)e, k ; P .7.54 (lob)e±, k. i 748 (lo)e, k, i, f, g 749 (8)e, k 833 (l)e, k; D 881 (4)e, k V --943 (5)e, k V -943 (3b)e, k , P 989 (a)e, k - --1031 (2)e, k 9<)0 (3)e, k -f05J (3)e, k • P 105~ (l)e, k loS8 (~)e, k 1057 (I)e, II; rU2 (o)e, k; r - --llSO «z)e. k; n . 1I45 (3)e, k --1205 (3)e, k; D 1~07 (:)e, It - -1270 (I)e, k j D 1264 (3)e, k 1264 (a)e, k -1298 (2)e, k; P 1304 (6)e, k 1298 (3)e, k 12\)6 (3ble, k -1393 (lje. k 1312 (l)e, k -1426 (3)e, k; D 1429 (6)e, k 1437 (2)e, k -13!3 (4b)e, k; D 1445 (4b)e, k 1456 (2)e, k 1450 (lb)e, k 2 40 (I)e, k; P 2S44 (l)e, k - -2877 (2le, k; P 2874 (4)e, 10 2870 (alk 2880 (lb)e, k 2955 (10)e, k ; P '957 (Iole, k, i 2965 (lole, k, i, q, p, 0 I 2960 (8)e, k 3004 (6b)e, k ; D I 3005 (Sb)e, k, i 3012 (6)e, k, p 3005 (a)e, k It ellu he seen from Tables 1 and II that the number of lines having frequency shifts below IlOO cm-' is ten in the Raman spectra of both I, 1-c1khloroethaue and J, 2. dkhlorocthauc. In the former case almost all the prominent lines persist ill the solid stale at low temperature and in the latter case some of the prouunent liucs disappear completely when the substapce is solidified. As mentioned earlier this disappearance of the Raman lines of 1, 2- dichloroethalle was first ohf>erved by lIIizushima (1938) and explained ou the hypothesis that the molecules having trans and other configurations coexist iu the liquid state and the 1110lecules are all of the trans type in the solid state. It was pointed out by Sirkar and Bishui (1945) that this explanation was not satisfactory and au alternative explallatlon based on the '8I8Unlption that soong11 associated molecules are present in tlte tiquid atld . 322 ---------Present author. 168 (Ib}e, P 275 (4)e±k; P 3~2 (3)e, k , P 408 (3)e, k; P 640 (6)e, k, i, P 688 (3}e, k; D 90 :- (de, k; r 977 (2)e, k, P 1054 (2)e, k; r 1088 (zu)e, k; ~ 7255 (Ile, k, f 1270 (2)e, k, r 1352 (z)e, k; D I442 (Sle, k; D 2930 (6)e, k; P 2987 (8b)e, k; D 30i2 is)e, k; P B. M. BI,hui TABUt II 276 (4) 4'10 (3) 6.<12 (6) 687 (4d) 978 (2) 1050 (o·su) 1090 (I) 1229 (o) 1271 (I) 1353 (0·7Su) 1438 (zd) 2929 (6) 2!J8S (5) 3"71 (0.25) Solid State at about-170·C Present author. 70 (I) k 163 (Ib) e, k 277 (I) e, k 322 (I) e, k 408 (2) e, k 640 (3) e, k 680 (2) e, k 9i7 (Ib) e, k 1054 (0) e, k 1442 (2) e, k 2937 (5) e, k 2987 (4) e, k 2996 (~) e,_k _,072 (0) e; k solid states ",as oLlend by the latter authors. In the case of I, 1-.dichlorocthane on the other hand there IS hardly any prohabilityof the exis-fence of two rotational isomers in the liquid state. Of course, we may vi.sua. lise two different configurations of the molecL1le, one 'eclipsed' aud the other 'staggered', as sho\\n ill FiS. 5, but only one such form IS s[.\ble. ct Fig. 5 This conclusion is dra\\u from the experimental results reported by GlQCkler and Sage (1941) in the case of OClaCHFCl. TIle single conn guratioD of this molecule should l'ield 10 Raman lines accorditlg to group theory and only 18 sucb lines are also IIctually observed _ From these results and bom other evidences Glockler aud Sage (1941) have concluded that probably the 'Ilta,gercd' configuration is stable ,ltd the 'eclipsed' one is unstable .. t4t. "*lOtto substituted ethane c~pound$. Hence in the case of f, x· <liebloroeth~e ako probably the '15U1ggen.'li.' co,ufiguratlO'u 1~ the ::,table oue. Siuce ,.ome of the hues are totally detA>larised the molecule h.l~ a plane of s1U'unetrr. but both the forms of the molecule ,have a plane of symmetry ond tberefol'f these data regarding the l)olarlsationj of the linels caUDot indicate definitely which of the two configuration~ is act~Uy present in the liquId. Tpe f.ct that all the Raman lines having fr uency shift" below nco em-I observed in the liquid state are also pruent in e lsolid state at about -170° C clearly indicates thaL only one of two config bOlls is pre~nt 111 the liquid state. If there were two rotationul Isomers, e population of one of them would depend on the temperature, and at low t peratures one of the isome1s would be converted into the other and <..onseql tty the Raman lines Yielded by it ~'ou1d disappear at the low temperatules. Hence the results obtamed in the present dichloroethane dearly indicate th.lt the pres Raman spectrum of this liquid is not due t isomers 'nvestlgation regarding 11 I-e of too many lines in the the presence of rotational The disappearance of some of the lines 0 I, 2-dl('hloroethane WIth the solidification of the "ubstance has ahcady beeu plain cd by Sirkul and BilOhul (1945) on a hypothesIs in which it was assumed thjt associdted pail s of molec.ules having a centre of symmetry are formed ill the solid slate. The Raman spectlum of I, 2- dichloroethane 111 the vapour state has been inve5hgatcd by Morino, Watanahe and Midtushima (1942). They have come to the conclusion that th~ gauche molecules are more ahundant than trall!:> molecules in the liquid lstate and the opposite IS true in the case of ga!Jeous ... tate. Previously Mizushima et al (1938) pointed out that in the solid state all the molecules are in the trans state a\1d that wbel1 the substance melts and the molecules have fleedom of rutation most of them assume tbe gaucbe form. It is. however, difficult to l1ndelstand how in the gal:>eous state \"hen .,uch a freedom I'> Jlreatel the number of molecules of gauche form diminishes III the hypothesis in which the presence of as&ociated molecules IS postulated, these facts can be understtlod easily because in the vapour state 1II0bt of the moleculd become single and the lines due to single molecules become more intense than those due to the associated molecules. In the solid state some of the line~ due to the associated molecules dlsappcal because tbe resultant associatecl molecule has a ceutle of symmetly and the obclllations giving rise to tbese lines are antisymmetric to the centre of symmetry. Of course, from chemical point of view. there may be some difficulty ill unders. taudital the nature of the linkage which has been aSlsumed to be responsible for the formation of the associated molecules by Sirkar and Bishui (194.5), but the ~ture of th' Raman spectra of the subitan<.e at the dUferent states CAuot be explmned by _um.w, the co-existence of rotational isomers. There ia 'Fo .... J, 110 oUser alternative than to assume the existence of stroDsl, ~ted Dlo1eeulC!'8, b«ause tbe results of pr*nl investisat.lon slilq'W that J S--tv4P-7 324 B. M. Bi,1aut even when no such jsomers can be present in the case of I. x-dicholoroethaB&, the nUlnber of Raman lines observed is too large for a single molecule. The appearance of two lines at 58 cm-1 and 8z cm-1 In the case of t, 2· dichloroethane and of one lit1e at 70 cm-1 ill tHe case of I, 1- dichloroethant in the solid state is probably due to vibrations of the associated pairs of molecules in which single molecule" oscillate against each other. These lines are differentiated from those due to lattice oscillations because virtual chemic..'allinkages are involved in these modes of vibrations. ACKNOWI.RDGMnNT The author is indebted to Prof. S. C. Sirkar, D.Se., F.N.l. for his kind interest and encouragement during the progress of the work apd to Prof. M. N. Saba, F.R.S. for kindly allowing him to use the photo-ental·ger at the University College of Science, Calcutta. IlfnIAN ASSOCIATION "'OR THI! CVlT!nTJON OF ScrIlN('It, 2W, BOWDAlAR STRJlfT, C,U,CtTT'J'A REFERENCES nil!lhUl, n. M (1948), Ind. J. 1'lIys , 22, 251 and Sanyal, S. n., Imi J. Ph~'$. t1, 233 ~ Glock1er, O. and Sag«' C. (1941), Jour. Chl'nt. Phys ,9,387 (1941). Kagat, M. (1934), AnnJlal1'ables of Constants etc Page 22. Mizl1shlma, S and Morino, Y. (193811) PIOC. llld Acad Sf. A, 8,315 and Morino, Y. and Norozi (1936) SCI, Papers. lust. Phys Chell!. RC,I£'QI ell (Tokyo) 29, 63 and 188 Morino Y. Watanabe, J and Mid?ushima, S (19~2) Sr Papers. In~t. Phys Chel» Research ('lokyo) 39, 401. Sirkar, S. C lIll(] Rishui, R. M. (1945), Ind. J Phys, ,g, 23· (J943), ]lTO(' Nat Illst. Sc. 01 India, 9, ~b7' 

The Raman Spectra of 1, 2- and 1, 1-Dichloroethanes in the Solid State

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The Raman Spectra of 1, 2- and 1, 1-Dichloroethanes in the Solid State

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