1-(Arylchloromethyl)pyridinium chlorides. Investigation by X-ray single crystal diffraction and semiempirical (PM3, AM1, MNDO) calculations

The molecular structures of 1-[chloro(2-methoxyphenyl)methyl]pyridinium chloride and 1-[chloro(3-nitrophenyl)methyl]pyridinium chloride were studied by X-ray single crystal diffraction and semiempirical calculations (PM3, AMI, and MNDO) in comparison with model compounds to give a deeper insight into reactivity of these pyridinium salts. Feasibility of the nucleophilic substitution of the chlorine atom in such cations finds its explanation in a relatively strong exocyclic N-C bond, which suppresses the substitution of the pyridine ring system. PM3 was found to be sufficiently accurate to predict the structure of such cations correctly. For both cations, nonsymmetric conformations were observed in crystalline phase being mainly determined by the chlorine substituents at the exocylic C-alpha atoms. The acidity of the methylene hydrogens promotes the formation of intermolecular C-H ... Cl- hydrogen bonds in both compounds. (C) 1998 Elsevier Science B.V.