Volumes of Activation for the Cycloaddition Reactions of Phenylhalocarbenes to Alkenes

摘要

The absolute rate constants for the cycloaddition reactions of three arylhalocarbenes to two alkenes have been measured as a function of pressure in the range 0.1 to 203 MPz. In all cases the observed rate constants were found to increase with increasing pressure. The magnitude of the derived activation volumes falls in the range of -10 to -18 cc/mol and does not depend on solvent. The results rule out a late, two-bond transition state and a bipolar single-bond transition state, but are consistent with the reversible formation of a carbenealkene complex or an early one- or two-bond transition state.