Probing the Anomeric Effect in O?C?N Systems Theory vs. Experiment: MO-ab initio Calculations and a Structural-Statistical Analysis

A combined computational (MO ab initio) and structural-statistical study of molecules containing the O? C? N moiety is presented. Aminomethanol, the simplest member of this series, was computed using GAUSSIAN-82 with the 3-21G and 6-31G* basis sets and with complete geometry optimization, as well as with MP3//6-31G*. A set of carefully selected molecules containing the O? C? N unit was retrieved from the Cambridge Structural Database (CSD), and its structural parameters were analyzed according to an established procedure. Comparison between experimental and computational data was thus made possible. Results are consistent with the co-existence of two unequal anomeric effects in this system: a strong n_N-σ*_{C? O} anomeric interaction, and a weak n_πO-σ*_{C? N} one. The ability of the two basis sets to reproduce the energies and structural characteristics of the stereoelectronic effects is assessed, including the significance of using polarization functions and the inclusion of correlation energy.