STUDIES OF INTER-AND INTRA-MOLECULAR DONOR-ACCEPTOR INTERACTIONS .2. INTERMOLECULAR CHARGE TRANSFER INVOLVING SUBSTITUTED PYRIDINIUM IONS

The intermolecular charge transfer (CT) interaction of various substituted aromatics and the iodide ion as donors, and substituted pyridinium ions as acceptors was studied. Relatively strong acceptor properties are displayed by the N-methyl-4-cyanopyridinium ion and with this ion a linear relationship is shown to exist between the ionization potential of the donor and the energy of the CT-transition as observed in the absorption spectrum. The complexes between N-methyl-4-cyanopyridinium ion and neutral aromatic organic donors are very weak as concluded from their equilibrium constants; the solvent dependence of the corresponding CT-bands cannot be correlated with solvent polarity parameters. It is shown that the double CT-band pattern of many pyridinium iodides is probably caused by the presence of two closely located vacant molecular orbitais in the pyridinium ion. © 1969.