The Solvation of Carbenes: π and <i>O</i>-Ylidic Complexes of <i>p</i>-Nitrophenylchlorocarbene

<i>p</i>-Nitrophenylchlorocarbene (PNPCC) was studied by laser flash photolysis with UV−vis detection in solution at ambient temperature. The π → p (316 nm) and σ → p (628 nm) absorptions of PNPCC were replaced in π- or O-donor solvents by absorptions due to π- or <i>O</i>-ylidic complexes or <i>O</i>-ylides. Donors included anisole, 1,3-dimethoxybenzene, 1,3,4,5-tetramethoxybenzene, diethyl ether, 18-crown-6, and dibenzo-18-crown-6. Suggestive evidence was also obtained for weak π-complexation of PNPCC by benzene. Computational studies aided in understanding the carbene complex and <i>O</i>-ylide absorption spectra, and they provided structures and energetics for these species.