The structural influence of two series of phosphorus-based diastereoisomers, e.g. a-aminobenzylphosphonates I and II (R = alkyl, Ph), on the 31P NMR chem. shift is evaluated by mol. mechanics calculation The results reveal that the intramol. local Van der Waals interaction energy of phosphorus atom (EVDW-P) calculated by MM2(85) program is the predominating factor governing the magnitude of the chem. shift of the phosphorus nucleus. The isomer, which has relative large EVDW-P value will show downfield 31P NMR chem. shift or vice versa. This empirical approach provides the experimental basis of a new and facile method for the elucidation of the absolute configuration of diastereoisomers with any asym. center. It has, therefore, significant theor. importance and potential practical value.

Key words: ORGANO PHOSPHORUS COMPOUNDS, ADDITION REACTION, SCHIFF BASE, IMINE, ABSOLUTE CONFIGURATION, PHOSPHORUS 31 MAGNETIC RESONANCE SPECTROMETRY, MOLECULAR MECHANICS, DIASTEREOISOMERIDE