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The thermal decomposition of hpropenylcyclobutane has been investigated in the temperature range 304348°C; the decomposition was homogeneous and first order. Two parallel reactions took place, an isomerization to yield 1-methylcyclohexene and a decomposition to yield ethylene and isoprene. The ratio of products from each reaction path was essentially independent of temperature. The Arrhenius equations for these two reactions were found to be : k(isoprene) = 1014.64 exp (-5 l,030/RT) sec-1, k(1-methylcyclohexene) = 1014.53 exp (-51,03O/RT) sec-1.

A laser flash photolysis/laser absorption technique has been used to generate and monitor SiH2 radicals in real time. We present preliminary results of a study of the rate of removal of SiH2 radicals in the presence of D2 in the temperature interval 268-330 K. The removal rate coefficient is found to be temperature independent in this range with a value (1.88 ± 0.17) X 10"12 cm3 molecule"1 s'1. The implications of this result for the temperature dependence of the reaction of SiH2 with H2 are discussed.

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The reactions of dimethylsilylene, SiMez, generated by laser flash photolysis from pentamethyldisilane and octamethyltrisilane, and detected via its 457.9 nm absorption, have been investigated with a number of oxygen containing molecules, including oxygen itself, carbon monoxide, water, alcohols, and ethers at 295 K. Some substrate molecules were deuterated. Apart from GO, all molecules reacted with SiMez with second order rate constants (in cm3 molecule-' s-l) in the range 7.7 x to 4.7 x lo-". While most of the reactions of SiMez studied went to completion those with dimethylether and tetrahydrofuran were partially reversible. The reaction of SiMep with oxirane was pressure dependent.The data are generally consistent with a mechanism involving initial formation of a donoracceptor, zwitterionic complex. In the case of reaction with alcohols, there is a small overall isotope effect, suggesting formation of a complex followed by rapid H-transfer, which only marginally affects the rate. In the case of ethers, complexes are formed which (i) may react further (MezSi . . . oxetane), (ii) may react further but also reversibly decompose (MezSi . . . oxirane), or (iii) do not seem to react further (MezSi . . .OMez, MezSi . . .THF) but partially redissociate.The donor-acceptor bond strength has been estimated in these last cases to be ca. 40 k J mol-I. Supporting arguments and mechanistic details of all reactions investigated are presented.

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