Dynamics of 1,3-Dipolar Cycloaddition Reactions of Diazonium Betaines to Acetylene and Ethylene: Bending Vibrations Facilitate Reaction

摘要

The activation energy of a 1,3-dipolar cycloaddition reaction is linearly related to the energy ΔE_d~≠ that is required to distort the dipole and dipolarophile to form the transition-state (TS) geometry. This discovery complements previous theories of dipolarophile reactivity, which emphasized the interaction between frontier molecular orbitals (FMOs) of the reac-tants. The correlation with distortion implies that the vibrational excitation of the reactants is an important feature of the mechanism. We have now explored the reaction dynamics of three typical 1,3-dipoles with acetylene and ethylene. In these six reactions, which span a range of 1,3-dipoles, barriers, and reaction energies, we find that specific vibrations must be excited to make the reaction possible.