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
✍ Scribed by Bunji Uno; Kenji Kano; Naoki Kaida; Tanekazu Kubota
- Publisher
- Elsevier Science
- Year
- 1989
- Tongue
- English
- Weight
- 466 KB
- Volume
- 45
- Category
- Article
- ISSN
- 1386-1425
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✦ Synopsis
Electronic spectra of 4-substituted pyridine N-oxides and their EDA complexes with iodine were studied. The substituent effect on the near u.v. tA~ 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-CI calculations. Based on the results mentioned above, the character of n-a type N-oxide --iodine CT complexes is also examined. The complex formation constants (log K) and pK, 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, values.