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 pK_a 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.