Carboethoxycarbene reacts with methanol-OD to form an ylide. The formation and decay of this ylide was monitored by ultrafast time-resolved IR spectroscopy. The formation and decay of the ylide is linearly dependent on the concentration of methanol-OD in acetonitrile with second-order rate constants of ylide formation (8.4 x 10(9)M(-1) s(-1)) and decay (1.4x 10(9)M(-1) s(-1)). Similar results were obtained with 1-butanol.