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The photolysis of inert matrix isolated methylene trithiocarbonate at 10 K has been shown to be a clean source of thioformaldehyde. The CH2S and CD2S molecules produced this way are indefinitely stable under these conditions and their FTIR spectra could be recorded. A normal coordinate analysis has been carried out and all the normal frequencies of both molecules have been assigned.

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This prrper is dedictrteil to Prqf'e~sor Hnrry E. Gut~tlitzg 011 the occ.n.siotz of' his 65th b i r t h~l q MANUEL TORRES, JUAN RIBO, ALLAN CLEMENT, and O R 0 P. STRAUSZ. Can. J. Chem. 61, 996 (1983). The conformational control of the Wolff rearrangement (WR) has bcen studied by Incans of a comparative study of the low temperature photolysis of argon-matrix isolated a-diazo ketones, 1, and of vinylcne thioxocarbonates, 2. Under these conditions thc s-E, s-Z conformational equilibrium of 1 will be hindered whereas 2 has a fixed s-Z conformation. The results indicate that the conformational control observed in the WR of a-diazo ketones is not per se a proof for a concerted mechanism and that a mechanism involving a ketocarbene intermediate is the most reasonable.MANUEL TORRES, JUAN RIBO, ALLAN CLEMENT ct ORO P. STRAUSZ. Can. J. Clicm. 61, 996 (1983). On a CtudiC le contrble conformationnel de la transposition de Wolff (TW) au moyen d'une Ctude comparative de la photolyse i basse tempkrature des a-diazo cCtones 1 et des thioxocarbonates de vinylhe 2, isol6s dans une matrice d'argon. Dans ces conditions, I'Cquilibre conformationnel s-E, s-Z du composC 1 sera emp&chC tandis que le composC 2 a une conformation s-Z fixe. Les rtsultats indiquent que le contrble conformationnel observe dans la TW des a-diazo cCtones n'est pas en soi une preuve de I'existence d'un mecanisme concert6 et qu'un mCcanisme impliquant un citocarbkne comme intermidiaire est plus raisonnable.[Traduit par le journal]The Wolff rearrangement (WR) of a-diazo ketones and a-diazo esters to ketenes can be brought about either photolytically, thermally, or catalytically and ketocarbenes are generally thought to be implicated as short-lived reactive intermediates in the photochemical and thermal reactions (1 -12).Unambiguous evidence for the intermediacy of ketocarbenes and carbalkoxycarbenes came from the detection of oxirenes as reactive intermediates in the WR (4, 10, 11) kinetic studies (7) as well as from the effects of the substituent upon nitrogen elimination (6). Moreover, molecular orbital computations predict a prohibitively high energy requirement for concerted nitrogen elimination (12). Also, the low temperature stabilization and direct esr.detection of a series of triplet state ketocarbenes from the photolysis of a-diazo ketones has been reported (1 3 -18). These observations are in agreement with molecular orbital predictions of a triplet ground state for these species, with a small singlet-triplet energy separation (19).A concerted mechanism for the WR would be in clear contradiction to the now well established transient formation of oxirene in a large number of photochemical WR (for a recent review, see ref. 20). Recently, however, Kaplan and Mitchell (21) have restated an earlier suggestion (22) of an alternative concerted mechanism for the decomposition WR sequence of those a-diazo ketones in which the intermediacy of oxirene was not detected. The a-diazo ketones may exist as two rotational isomers of the type s-E and s-Z and the propose...