The combination of laser flash photolysis and product analysis demonstrates that even though (phenoxymethyl)chlorocarbene reacts with its diazirine precursor with a substantial rate constant of 3.5 x 10(8) M(-1)s(-1), the predicted azine product is not formed. These results indicate either carbene/diazirine reversibility or subsequent hydrogen migration of the carbene/diazirine adduct. Also, a rate constant of 2.0 x 10(7) s(-1) for the 12-hydrogen atom migration in (p-nitrophenoxymethyl)chlorocarbene has been determined using the pyridinium ylide technique.