An electron impact study of ionization and dissociation of trimethylstannanes

Abstract

Appearance potentials of ions from a series of trimethylstannanes were measured. Combination of these data with molecular and radical heats of formation, with the assumption of zero excess energy on electron impact ionization, yields a value of Δ H f[(CH 3) 3Sn] = 32 ±6. Also from these data an ionization potential of the trimethylstannyl radical of 6.8±0.3 eV is derived, in good agreement with direct measurement. The dissociation energies of the (CH 3) 3Sn-X bonds are shown to be about 10-12 kcal·mole -1 lower than in the corresponding (CH 3) 3C-X bonds. value of Δ H f[(CH 3) 3Sn] = 32 ±6. Also from these data an ionization potential of the A considerable fraction of the available data on bond dissociation energies, molecular ionization potentials, and free radical ionization potentials has come from studies of the behavior of molecules subjected to electron impact. Such knowledge has proven to be of interest and importance in questions of electronic structure and of rates and mechanisms of chemical reactions. However, most of this large body of energetic data pertains to molecules, radicals, and ions that are generally thought of as belonging to the realm of organic chemistry. In the rapidly growing field of organometallic chemistry very little such energetic data is available for guidance in structural, mechanistic and rate considerations. Indeed, in many areas of organometallic chemistry not even the standard heats of formation of the stable compounds are known. In the case of organotin compounds, however, a body of thermochemical data is available (although some of the older work, as recently pointed out, is unreliable) and mes feasible electron impact studies directed toward the determination of the energetic properties of the organotin molecule, ions, and free radicals. In this paper we describe a study on the ionization and dissociation of some trimethyltin derivatives by electron impact. Some preliminary results of this study were published previously.