ORGANIC zyxwvutsrqp MASS SPECTROMETRY, VOL, 21, 171-174 (1986) Electron Impact Induced Fragmentations of 2-Chlorovinyl Methyl Sulphides C. Paradisi, G. Scorrano and A . Visentini Centro Meccanismi Reazioni Organiche del CNR, Dipartimento di Chimica Organica, Via Marzolo zyxw 1, 35131 Padova, Italy P. Traldi IPELPICNR, Corso Stati Uniti 4, 1-35131 Padova, Italy A series of 2-chlorovinyl methyl sulphides, CH,SCR1=CRZCl (R1, R2=H, Me, Et, t-Bu, Ph; R'=H, R2 zyxwvutsrqp = CH,) has been analysed under electron impact conditions. The most significant common fragmentations involve primary loss of C1' and methyl radicals. Analysis of the phenyl-substituted derivative suggests that loss of CH,' is a lower activation energy process than loss of C1'. The characteristic loss of CH3SCl from the same derivative has been examined with respect to the structure of the resulting fragment by means of suitable model compounds. INTRODUCTION The reaction of alkynes with organic sulphenyl chlorides RSCl (Scheme 1) constitutes the best synthetic entry to 2-chlorovinyl thioethers. ,l The scope and mechanism of this reaction have been thoroughly investigated;' these studies have led most notably to the characterization of thiirenium ions, species of novel and interesting structure, which form as intermediates in the addition reaction.' zyxwvu Scheme 1 Although the electron impact (EI) induced fragmentations of thioethers, including some vinyl derivative^,^ have been extensively inve~tigated,~ the behaviour of 2-halovinyl thioethers under electron impact conditions is little known.' We report here some relevant results of a study of the electron impact induced fragmentations of a series of 2-chlorovinyl methyl sulphides characterized by different sub- stituents on the double bond. RESULTS AND DISCUSSION Compounds 1-6, prepared according to the reaction of Scheme 1, were analysed under El (70eV) conditions. The D-labelled analogue of 2, compound 7, was also included in the series. The most abundant and significant 70 eV EI-induced fragmentation products of compounds 1-7 are reported in Table 1. All compounds form abundant molecular ions which, for compounds 1-3 and 7, give rise to the base peak in the mass spectrum. The general fragmentation 0030-493X/S6/040171$04$05 .OO zyxwvutsrq 0 1986 by John Wiley & Sons, Ltd. c1 CH,, / /c=c R' CH,S 1: R'=R~=H 7 zy 2: R' = CH,, R' = H 3: R'=R~=CH, 4: R' = R* = C,H, 6: R' = R~ = C,H, \ 2' /C=C RZ CD,S ' H \ z 5: R' = R2 = t-C,H, pattern, reported in Scheme 2, was obtained by means of linked scan experiments and of the analysis of the D-labelled derivative 7. Two primary decomposition pathways are common to all the compounds examined, i.e. primary loss of chlorine and of methyl radicals. The variation with electron energy of the relative abundances for these two competing decom- positions has been examined for the stilbene derivative 6, for which no ambiguity exists as to the origin of the methyl radical lost. The results, shown in //- - CH,' [c3H;sR'R21' * -CI' \ -C1' [C2SR'R2CI]' zyx a #&, ?q%S C e Scheme 2 zyxw Received 8 May 1985 Accepted 5 July 1985