Electronic spectra of 4-substituted pyridine N-oxides and their EDA complexes with iodine were studied. The substituent effect on the near u.v.1A1intramolecular CT bands of the N-oxides and on the blue shifted iodine bands caused by CT complex formation are discussed in terms of a general equation, theoretically derived in order to describe the substituent effect on electronic spectra by means of substituent constants. The results are quite successful and supported by semi-empirical SCFMO-CI calculations. Based on the results mentioned above, the character of n-σ type N-oxide-iodine CT complexes is also examined. The complex formation constants (log K) and pKavalues of the N-oxides correlate especially well, indicating that the CT interaction mechanism cannot be neglected in proton addition reactions such as hydrogen bonding and pKavalues. © 1989.
Uno, B., Kano, K., Kaida, N., & Kubota, T. (1989). New description of the substituent effect on electronic spectra by means of substituent constants-VI. Utraviolet spectra of 4-substituted pyridine N-oxides and blue shifted iodine bands of their EDA complexes with iodine. Spectrochimica Acta Part A: Molecular Spectroscopy, 45(9), 937–943. https://doi.org/10.1016/0584-8539(89)80151-5