Quantenchemische untersuchungen zum mechanismus der elektrophilen substitution—III : Zur stabilität und struktur von [H,CH3]-σ-komplexen (ipso-Addukten) protonierter methylbenzole

The H,CH₃]-σ-complexes of toluene and the three isomeric xylenes formed by electrophilic H⁺-attack on substituted positions or by H-shifts from the isomeric σ-complexes are studied by the CNDO/2-FK MO method. These complexes (ipso-adducts) occur as minima on the energy surfaces in agreement with the results for H,H]-σ-complexes. Their geometrical structure and tendencies of formation are presented and a comparison with experimental results in solution is given. Suggestions for different stabilization of the isomeric σ-complexes of substituted benzene by solvent molecules are found.