Chemical Reactivity of Alkenes and Alkynes As Seen from Activation Energies, Enthalpies of Protonation, and Carbon 1s Ionization Energies

摘要

Electrophilic addition to multiple carbon−carbon bonds has beenninvestigated for a series of twelve aliphatic and aromatic alkenes and thencorresponding alkynes. For all molecules, enthalpies of protonation andnactivation energies for HCl addition across the multiple bonds have beenncalculated. Considering the protonation process as a cationic limiting case ofnelectrophilic addition, the sets of protonation enthalpies and gas-phase activationnenergies allow for direct comparison between double- and triple-bondnreactivities in both ionic and dipolar electrophilic reactions. The results fromnthese model reactions show that the alkenes have similar or slightly lower enthalpies of protonation, but have consistently lowernactivation energies than do the alkynes. These findings are compared with results from high resolution carbon 1s photoelectronnspectra measured in the gas phase, where the contribution from carbons of the unsaturated bonds are identified. Linearncorrelations are found for both protonation and activation energies as functions of carbon 1s energies. However, there arendeviations from the lines that reflect differences between the three processes. Finally, substituent effects for alkenes and alkynesnare compared using both activation and carbon 1s ionization energies.