Charge-transfer interactions in some 2-, 3-, 4-substituted N-methylpyridinium iodides and tri-iodides

Abstract

The charge transfer (CT) interactions involving the substituted pyridinium ion are of a remarkable biological interest. In particular the pyridinium ions having substituents in position 3 of the heterocyclic ring constitute models for the study of similar, more complex structures. In this paper some spectral characteristics are reported which show such CT interactions between N-methyl-2-, -3-, -4-metoxypyridinium ions and iodide ions, and between N-methyl-2-, -3-, -4-tiomethylpyridinium ions and iodide and tri-iodide ions. The pyridinium ions substituted in position 3 turned out to be the strongest electron-acceptors. The 1H N.M.R. investigations concerning the N +-CH 2 chemical shift confirmed that : I. a substituent of the -OCH 3 and -SCH 3 type in the pyridine ring causes a rise in the negative charge on the nitrogen in relation to the position in the ring according to the sequence 2 > 4 > 3 ; 2. the substitution of the -O-CH 3 group with the -S-CH 3 group seems to modify the nitrogen charge-density only when the substitution takes place in position 2.