Self-addn. of iodide to pyridinium nucleus can take place for 2-chloro-1-dodecyl pyridinium iodide (CDPI) in CH2Cl2 upon irradiation The structure of product isolated was shown to be the para-isomer with spectroscopic methods. From electron spectroscopic results, Kosower postulated that the pyridinium iodide can exist in the form of self-addn. product through intermediates of charge-transfer complex and tight free radical pair, but in the ground state the balance trends to ionic form, therefore the addition product was not isolated yet. The fact that we were able to isolate a stable self-addn. product I from CDPI, might be attributed to the existence of chlorine causing the decrease of electronic d. at nucleus thus stabilizing the I-C bond. The fact that isolation of addition product provides a more direct evidence for the charge-transfer mechanism in the action of Kosower polarity probes.

Key words: PYRIDINE P, NMR SPECTROMETRY, IODIDE, ORGANO CHLORIDE COMPOUNDS, FREE RADICAL, PHOTOELECTRON SPECTROSCOPY, C12 COMPOUNDS, CHARGE TRANSFER COMPLEX, POLARITY, PROBE ELECTRODE