Photolysis of methyl 2-diazo(2-naphthyl)acetate releases singlet 2-naphthyl(carbomethoxy)carbene. The singlet carbene relaxes to the lower energy triplet state within 350 ps−1 ns. Singlet to triplet carbene intersystem crossing is much faster than Wolff rearrangement to the corresponding ketene. The barrier to Wolff rearrangement of the spin-equilibrated carbene is 3.4 kcal/mol in hexafluorobenzene. In this system, ketene is formed from the carbene and is not formed to a significant extent from an excited state of the diazo compound.