Peter F. Rogerson

Tetrahedral C4R4+• in the mass spectral fragmentation of thionessal dioxide

Abstract On electron impact, tetraphenylthiophene-1,1-dioxide (thionessal dioxide) loses SO 2 to give (C 6 H 5 ) 4 C 4 +• . The p -fluoro labeling technique has been used to determine whether this ion is acyclic, or whether it attains square or tetrahedral symmetry. The energetics for the loss of SO 2 are sufficiently similar to those for the loss of CO from tetracyclone that the C 4 R 4 +• ion attains very nearly the same, i.e. distorted tetrahedral, symmetry.

The electronic absorption and ionization potentials of carbosilanes. the question of 1,3(d-d interaction in the excited state

Abstract The electronic absorption spectra of carbosilanes containing the group have been measured. The cyclic carbosilanes (Me2SiCH2)n n=2, 3, 4, and 2,2,6,6-tetramethyl-2,4,6-trisilaspiro[3.3]cyclophetane exhibit large bathochromic shifts relative to analogous acyclic carbosinales. Electron impact-ionization potential measurements demonstrate the shifts are primarily a manifestation of ground state destabilization, rather than excited state stabilization originatingfrom 1,3(d-d) interaction. The spectra of Si-phenylated carbosilanes confirm this conclusion.