Photochemical generation and matrix-isolation detection of dimethylvinylidene

We report the spectroscopic characterization of dimethylvinylidene, (CH3)(2 )C=C:, generated within an argon matrix at 14 K from a bisperoxyester precu rsor. The carbene was identified by comparison of the experimental IR spect rum with vibrational frequencies computed at the B3LYP/6-31G(d) level. Chem ical trapping of the carbene within a 9% CO/Ar matrix to form dimethylpropa dienone supports this analysis. Additional products produced during photoly sis were identified by comparison to the appropriate computed vibrational f requencies. The potential energy surface of dimethylvinylidene and its intr amolecular rearrangement products, 2-butyne and methylcyclopropene, were al so investigated computationally at the B3LYP/6-31G(d) level. A spin-state a nalysis of this carbene using a variety of computational methods (CCSD(T), B3LYP, MP2) indicates the singlet state is more stable than the triplet by similar to 45 kcal mol(-1). We anticipate the bisperoxyester precursor used here will be a convenient and general way for initiating future studies of alkylvinylidenes under matrix-isolation conditions.