Chemical and Physical Properties of 9-Xanthylidene: A Ground-State Singlet Aromatic Carbene

Article abstract of DOI:10.1021/ja00300a028

Irradiation of 9-diazoxanthene (DAX) leads to loss of N2 and formation of 9-xanthylidene (XA).This carbene was detected at low temperature in a frozen glass and by laser transient absorption spectroscopy.It reacts rapidly with alcohols to form ethers and with styrenes to give cyclopropanes stereospecifically.At room temperature, XA does not react significantly with hydrocarbons, but at elevated temperature, an insertion reaction characteristic of a singlet carbene is observed.Rate constants for these and other reactions are reperted.The data show that XA is a ground-state singlet carbene with a triplet state at least 4 kcal/mol above the singlet.This finding is incorporated into a general explanation of aromatic carbene reactivity.