Spectroscopic evidence for hydrogen-bond formation between methanol and halogenoalkanes

Abstract

Addition of mono chloro-, bromo- or iodo-alkanes to methanol in tetrachloromethane results in the loss of the OH stretching bands characteristic of monomeric solvent and the growth of distinct bands due to RhalHOMe hydrogen-bonded complexes. Equilibrium constants (K), estimated from the spectra, show that the hydrogen-bond strength increases in the series RCl, RBr, RI. Shifts and equilibrium data for nitromethane and cyanomethane have been obtained for comparative purposes. The band maxima increase monotonically and almost linearly with K for this series of weak bases.

Concomitant decreases in the carbon–halogen stretching bands have also been monitored. The significance of these results to the mechanism of S_N1 reactions is discussed.