Investigation of Markovnikov reactions of alkenes via ABEEM-σπ model

Electrophilic additions of HCl to a series of asymmetric alkenes in the gas phase have been investigated in the light of the ABEEM-σπ model and high-level ab initio method. We demonstrated well the regioselectivity of the electrophilic reactions by means of the ABEEM-σπ model on the basis of local HSAB principle and maximum hardness principle. According to the charge distribution in the initial state of alkenes not only regioselectivity has been explained reasonably, but also an interesting phenomenon has been observed that alkenes with electron-donating substituents show a clear regioselectivity, but those with electron-withdrawing ones do not display a clear preference for anti-Markovnikov or Markovnikov addition.