Conformation preferences in nitro-alcohols: possible donor–acceptor interactions

Abstract

By means of ¹H and ¹³C n.m.r. coupling constants, dilution studies, the effect of solvent, and limited i.r. studies, the configuration and conformation in a group of diastereoisomeric nitro-alcohols, such as 3-nitrobutan-2-ol are assigned. The question of interest concerns the effect of intramolecular hydrogen bonding between nitro and hydroxy on conformation. This effect proved to be weak. The OH n.m.r. signal was split into a doublet, in certain cases; the magnitude of the splitting was not indicative of prevalent hydrogen bonding, in agreement with hydroxy chemical shift, and with vicinal proton coupling constants. The ¹⁵N chemical shifts were similar to nitromethane, and not sensitive to the state of isomerism. Deuterium for hydrogen exchange occurred at the carbon bearing the nitro group with high retention of configuration.