AM1 MOLECULAR-ORBITAL STUDY OF THE TRANSMISSION OF ELECTRONIC EFFECTS IN THE 5-MEMBERED HETEROAROMATICS - PROTON AND HYDRIDE ION AFFINITIES OF 4-SUBSTITUTED AND 5-SUBSTITUTED (2-HETEROAROMATIC)METHYL ANIONS AND CATIONS

The proton and hydride ion affinities of a series of the benzyl-like anions and cations of 4- and 5-substituted 2-methyl 5-membered heteroaromatic compounds have been calculated by the semiempirical AM1 MO method. Calculations included para- and meta-substituted toluenes, similarly substituted 1,3-pentadienes, and 3-aza-1,3-pentadienes as various models for the possible pathways for the effect of the substituents to be transmitted to the reaction site. There was excellent correlation between the 4-substituted compounds and the m-toluenes and between the 5-substituted compounds and the p-toluenes. Compared to the other ring atoms, substituents at either the 4- or 5-position have little effect on the change in the charges on the heteroatoms in going to either the cation or anion of the heteroaromatic compounds. It was concluded that transmission of electronic effects is primarily through the carbon skeleton with little if any through the heteroatom.