Insight into Markovnikov regioselectivity rule via molecular face and ABEEM‐σπ theory

Abstract

Electrophilic additions of HCl to a series of asymmetric alkenes in the gas phase are investigated by the Molecular Face (MF) theory and ABEEM-rp model. The interesting features of regioselectivity for these reactions are characterized by the electron density (ED) encoded on the MF of alkenes and charge distribution of alkenes obtained via the ABEEM-rp model, respectively. It is then demonstrated that for a series of alkenes, the Hammett constant r p (substituent constant) has a good linear correlation with K ED , where K ED is character of the ED at the p region in the initial state of alkenes. Comparison between investigations using MF, ABEEM-rp, molecular electrostatic potential, and DFT theories, in essence, give similar conclusions for explaining the regioselectivity of the electrophilic additions to alkenes, although from different points of view.

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

“…Activation energies in the gas phase are not readily available but may be obtained from theoretical calculations. Calculated activation energies for the addition of HCl have been reported previously for some of the smaller alkenes in this study, i.e., for ethene, 13,26−28 propene, 13,26−29 and 1-butene, 28 and we extend these studies to our full set of alkenes and alkynes. It is noteworthy that no experimental or theoretical investigations have been published for HCl addition to alkynes in the gas phase.…”

Understanding chemistry: from “heuristic (soft) explanations and reasoning by analogy” to “quantum chemistry”

“…That is, they are consistent with the available experimental data but they do so by happyor unhappycoincidence. [254][255][256] Examples include the so theories that "explain" the stability of the hexagonal structure of benzene, 90 and the attractive effects of some otherwise steric effects due to favorable dispersion effects. 210,257 And are there cases of hard theories that should not be made qualitative?…”