H-1 NMR studies of rotational isomerism in phosphonic analogues of aspartic acid

Aspartic acid and its phosphonic acid analogues exhibit rotational isomeris m around the C(2)-C(3) bond in solution. The characteristic vicinal proton- proton coupling constants in their H-1 NMR depend on the population of rota mers. By the use of these coupling constants, which are correlated with two different sets of parameters describing rotamer populations, namely (3)J(H H)(g) = 2.3 (or 2.4), (3)J(HH)(t) = 13.9 (or 13.3) and (3)J(HP)(g) = 4.2, ( 3)J(HP)(t) = 33.0 Hz, one can obtain full information on the population dis tribution of the rotamers in the examined compounds. Copyright (C) 2000 Joh n Wiley & Sons, Ltd.