The fragmentation processes of P=S compounds upon electron impact include the following bond-forming reactions :(i) molecular ion rearrangement of the type -P(:S)O-R -P(:O)S-R, (ii) bond formation between substituents (especially aryl groups) on phosphorus, (iii) loss of SH. from the molecular ion where the hydrogen can be derived from an alkyl or an aryl group, and (iv) hydrogen rearrangement to give the phenol molecular ion (or an isomer) in compounds having a phenoxy-substituent.THE propensity of organosulphur compounds to undergo rearrangement upon electron impact and the fact that bond-forming reactions involving atoms other than hydrogen have been observed in ph~sphines,~, phosphine o x i d e ~, ~' ~ phosphites,4 phosphate^,^ and phosphonates t i led us to examine the mass spectra of compounds (1)-(XII). Methyl and aryl substituents were preferred to larger alkyl groups since hydrogen rearrangements, which are common ' in the spectra of phosphorus compounds containing alkyl substituents, could obscure the more interesting skeletal rearrangement processes.

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This study is concerned with the effect of phenyl substitution upon the mass spectral behavior of ,/3-unsaturated ketones as an example of a substance with three potential charge-retaining sites (carbonyl, double bond, aromatic ring). Compounds of the type C6Hs(CH2)"CH==CHCOCH3, = 2-7 (I-VI), are examined.In general, the 70-eV spectra of these compounds are dominated by peaks at m/e 91 (tropylium ion) and m/e 43 (a cleavage). At nominal 12 eV, however, lower activation energy rearrangement reactions are favored.

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