Thermal isomerization of an olefin to a carbene is observed only in a few strained olefins. Attempts to observe a 1,2-silyl migration to form a carbene from a simple olefin were not successful. The olefins studied are stable at lower temperature and decomposed to smaller molecules at higher temperature probably via a radical process. The gas-phase thermal behavior of a series of organic and organosilicon compounds was studied by stirred-flow reactor (SFR) pyrolysis. Kinetic parameters were determined in the gas phase for various hydrocarbons and organosilicon compounds. The activation energies and log As of the compounds studied are in the normal range of olefinic cis-trans isomerization proceeding by a singlet biradical mechanism;The substituent effect on the thermal isomerization of olefins was discussed. The substitution of phenyl, t-butyl, and trimethylsilyl groups on the double bond lowers the olefinic cis-trans isomerization Oil, Gas, and Energy;A new reaction, gas-phase thermal isomerization of a silacyclobutene to silylallene, was discovered. The mechanism of the isomerization was studied by deuterium-labeling experiments;Intermediates containing silicon-nitrogen double bonds were generated in the gas phase by [beta]-elimination of trimethylmethoxysilane and retroene elimination of propene. The 1,2-silyl migration of silanimine to aminosilylene was observed. This is the first observation of a silanimine-to-aminosilylene isomerization. The aminosilylene formed was trapped by 1,3-butadiene and the structure of the trapping product was proven by comparison of its spectroscopic data with that of an authentic sample synthesized by an independent route. The isomerization of silanimine to aminosilylene by 2,3-allyl migration was not observed. Dimers of silanimine are formed in the absence of trapping reagents;Different approaches to silicon-nitrogen double bond were also explored. Attempts to obtain evidence for silapyridine, an unknown compound, both theoretically and experimentally, were not successful.