Infrared spectra of various types of organosulphur compounds have been examined and group frequencies arising from C-S, S-S, N-S, 0-S, and C=S stretching vibrations ha\e been assigned and discussed. The C-S bands of thioketals and S-S bands of tri-and tetra-sulphides show splittings due to vibrational coupling. The 0-S and N-S stretching frequencies are found around 890 and 820 cm-' respectively, values which are much higher than the C-S stretching frequencies. Potassium alkyl xanthates exhibit the asymmetric and symmetric stretching frequencies of the CS2-ion. The splitting of C-0 and C=S stretching bands in dialkyl dixanthogens have been interpreted in terms of the Fermi interaction with the combination tone of C-S and S-S stretching vibrations and with the overtone of S-S stretching vibrations respectively. The relative intensity of the C=S stretching bands in a few derivatives show marked dependence on the electronegativities of the elements directly

Borohydride reduction of the bi-enone (1 ) gave the structurally and mechanistically interesting compounds (4) and (5a-c) resulting from intramolecular carbon-carbon coupling. Intramolecular photocycloaddition in the bienone(1) has been reported to be inefficient presumably because of the competing facile , b' C-C cleavage> With a view to preparing the biallylic alcohol (2), required for further studies of intramolecular photocycloadditions, we reduced the bienone (1) with sodium borohydride in tetrahydrofuran (THF). The biallylic alcohol (2) (m.p.-f 212-215 O C ; m / e 444) was obtained in only 15% yield. The major products were the hemiacetal (3) (35%;

Solvent effects on the keto-enol equilibria of ethyl acetoacetate, acetylacetone, ethyl cyclopentanone-2-carboxylate, and methyl 4-metliylcyclopentane-1,2-dione-3,4,5-tricarboxylate have been st~idied by ultraviolet spectroscopy. The extent of enolization is mainly determined by the stabilization of the keto form by local association with polar or protondonating solvent molecules, just as in the case of n -+ T* transitions and infrared stretching frequencies. Solvent effects on infrared spectra reveal useful infornlation regarding the characteristic Ireq~iencies of the tautomers.Keto-en01 tautomerism has been investigated extensively by ultraviolet (I), infrared (2), and n.m.r. (3) spectroscopy. Keto-en01 equilibria are extrenlely solvent sensitive and the proportion of en01 form is found to be much greater in non-polar solvents such a s cyclohexane than in polar solvents such as alcohol or water. This is probably due to the stabilization of tlie lteto for111 by polar solvents through local association. Recently in this laboratory we have investigated the solvent effects on the n -+ a" transitions of several cliromophores and have evaluated contributions from different factors (4). These studies clearly indicate that solvent effects on the n -+ a" transitions are nlainly controllecl by local association between the solute and the solvent nlolecules and tliat the magnitude of tlie solvent blue shifts are determined by the polarity and/or proton-donating ability of the solvents. Studies of the solvent effects on infrared group frequencies have also shown tliat local association is an important factor in the determination of the solvent shifts (5). I t was consiclered interesting to sj~ste~natically investigate the lteto-en01 equilibria of a few systems in several solvents and correlate the observed effects with the solvent effects on the 7% -+ a:Qransitions and the stretching vibration frequencies of carbonyl groups. We have now studied the lteto-en01 equilibria of ethyl acetoacetate, acetylacetone, ethyl cyclopentanone-2-carboxy!ate, and methyl 4-~nethylcyclopentane-l,2-dione-3,4,5-tricarboxylate (I) in solvents of varying degree of polarity or/and proton-donating ability. EXPERIMENTALCommercial samples of ethyl acetoacetate and acetylacetone mere ~ised after suitable purification. Ethyl cyclopentanone-2-carboxylate was prepared by the procedure described in Orgaltic Syntheses (6) and methyl 4-metl~ylc):clopentane-l,2-dione-3,4,5-tricarbosylate was prepared according to the method of Ch~lang and M a (7). All the solvents were purified and fractionated before use.Ultraviolet absorption spectra were recorded with a MiIger U\,ispek, model H 700, spectrophotometer. Thc infrared spectra were recorded with a I'erkin-Elmer infrared spectrometer, model 137, with sodium chloride optics.Percentage of the en01 form was calculated from the extinction coefficieilt in the ultraviolet spectrum using the formula 1 0 0 (~~/~~) , where 6, is the observed molar extinction coefficient and s, the assumed value for the chromo...

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