Hydrogen bonding in pyridine N-oxides

Abstract

Hydrogen bonding of 2-cyano-, 3-iodo-, and 3,4-dimethyl-pyridine N-oxides with methanol in solution in 2,2,4-trimethylpentane has been investigated by u.v. spectroscopy. Association constants and ΔH°-values were determined in the temperature range 24–48°. The blue shift of the first π–π* transition in pyridine N-oxides, observed when changing the solvent from a hydrocarbon to an alcohol, is interpreted as being due to a stabilization of the ground state by hydrogen bonding. In the system 3,4-dimethylpyridine N-oxide and methanol in 2,2,4-trimethylpentane, a 1 : 2 complex is formed besides the usual 1 : 1 complex. Hydrogen bonding between 3-chloropyridine N-oxide and methanol has been studied in C₂Cl₄ by both u.v. and i.r. techniques. There is a satisfactory agreement between results of the two methods.