New description of substituent effect on electronic spectra by means of substituent constants-VI. Ultraviolet spectra of 4-substituted pyridine N-oxides and blue shifted iodine bands of their EDA complexes with iodine

Article abstract of DOI:10.1016/0584-8539(89)80151-5

Electronic spectra of 4-substituted pyridine N-oxides and their EDA complexes with iodine were studied.The substituent effect on the near u.v. ¹A₁ intramolecular 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-Cl calculations.Based on the results mentioned above, the character of n-? type N-oxide-iodine CT complexes is also examined.The complex formation constants(log K) and pK_a values 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 pK_a values.