Potential Energy and Spin-Spin Coupling Constants Surface of Glycolaldehyde

The potential energy surface of the simplest carbohydrate, glycolaldehyde, was investigated at the secondorder Møller-Plesset (MP2) level of theory, and the rotation barriers between them were calculated. Four local minima and six transition states were found. Next, the conformational dependence of the indirect nuclear spin-spin coupling constants was studied by means of density functional theory (DFT) using the B3LYP functional. For selected cases, the coupling constants calculated by means of DFT were compared with those obtained with coupled-cluster singles-and-doubles (CCSD) theory. The influence of rotation about the CC and CO bonds (with the remaining coordinates relaxed) on the spin-spin coupling constants was investigated, and the resulting curves were fit to a truncated Fourier series. The resulting expressions may help to determine the conformation of carbohydrates and their derivatives from the spin-spin coupling measurements. The relationships between coupling constants and dihedral angles were discussed and compared, whenever possible, with experimental trends.