Charge transfer interactions of heteroaromatic compounds: Part 5.—Complexes between pyridine-1-oxides and halogens

Abstract

Charge transfer complexes between pyridine-1-oxides and halogens in CCl4 have been investigated spectrophotometrically. Stability constants are reported for complexes between Br2, I2, IBr and ICl as acceptors and substituted N-oxides as donors at 30°C. These constants follow a linear free energy relationship with the σ values of the substituents in the donor ring for all the acceptors. The shift of the vibrational absorption of the N—O group on complexing is also reported.

The results are compared with the pKa values of the donors and with the corresponding parameters for pyridine complexes and are discussed in terms of steric and electronic effects. All the results are in agreement with the generally accepted n→σ* nature of these complexes, with some involvement of the π-orbital of the donor.