A LASER FLASH-PHOTOLYSIS STUDY OF CARBONYL YLIDES OF ARYLCHLOROCARBENES - KINETICS AND REVERSIBILITY OF THE FORMATION, CYCLIZATION, AND CYCLOADDITION

Carbonyl ylides formed from (p-nitrophenyl)chlorocarbene or phenylchlorocarbene and acetone or benzaldehyde have been studied by laser flash photolysis. The rate constants for the formation of these ylides, for their cyclization to oxiranes, and for some addition reactions have been measured. Electron-withdrawing substituents on the carbene increase the rate of ylide formation and decrease the rate of cyclization. The trapping of carbonyl ylide by para-substituted benzaldehydes gave a Hammett's ρ value equal to +1.0. The dual role of benzaldehyde, first as a constituent of the ylide and second as a trapping agent, has been demonstrated. Kinetic analysis indicates that an equilibrium exists between the phenylchlorocarbene, the acetone, and the corresponding ylide, with an equilibrium constant around 0.27 M−1 at 300 K. © 1990, American Chemical Society. All rights reserved.