Alan E. Sopchik

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

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.

Carbon-13 nuclear magnetic resonance studies of aromatic compounds: comparison of hydrogen bonding effects in phenols, anilides, and anilines

Two- and three-bond 13C n.m.r. coupling constants to 1H are reported for ring-substituted phenols, anilides, and anilines, plus limited data for thiophenols. The magnitude of the three-bond coupling constants to the phenolic hydroxy were rather insensitive to structural variations designed to alter the geometry of the coupled nuclei and raises the question of the exact geometric dependence of 3J on geometry. For acetanilides, the difference in magnitude between 3Janti and 3Jsyn is small. For anilines, the data are not suggestive of a geometric relationship. Thiophenols are similar to phenols. The influence of substitution on coupling constants between ring carbons and hydrogens is discussed briefly. Chemical shifts are reported for 16-ortho-substituted aromatic compounds.