Singlet and Triplet Dimesitylcarbene

Article abstract of DOI:10.1021/ja00315a014

The triplet states of essentially all diarylcarbenes react with substrates such as methanol or their parent diazo compounds both of which are thought to be specific quenchers for the singlet state.To rationalize these results, investigators have proposed that the singlet and triplet states of these carbenes are linked by efficient equilibria.In this kinetic study we have found that the singlet and triplet states of dimesitylcarbene exhibit quite distinct chemistries.The singlet state alone reacts with methanol, 1-propanol, and 1,3-cyclohexadiene, while the triplet carbene dimerizes to give olefin or, for example, reacts with oxygen.No evidence was found for reaction of the triplet carbene via the singlet manifold.Arguments are presented to explain the enhanced free energy difference between the spin states of this carbene and the relative persistence if its triplet.