Stereochemistry of organophosphorus compounds. XVI—configuration and conformations of 2‐substituted 2‐oxo‐(thio)‒3‒phenyl‒5‒methyl‒1,3,2‒oxazaphospholidines. Applications of 1H NMR Eu(dpm)3 shifts and LCAO MO EHM calculations for stereochemical study. Modified Karplus type function for 3J(HH′) in heteroatomic moieties

Determination of the configuration and preferable conformations of a series of 2‒substituted 2‒oxo(thio)‒3‒phenyl‒5‒methyl‒1,3,2‒oxazaphospholidines by 1H NMR, 1H{31P} double resonance NMR and 1H{31P} {CH3} triple resonance NMR is discussed in detail. As the first step for configurational assignment Eu(dpm)3 paramagnetic shift values are used. The study of the temperature dependence of the 3J(PNCH) coupling constants shows that compounds of the cis series adopt the semi‐chair conformation, but those of the trans series show considerable contributions from alternative conformations. Detailed analysis of the proton‐proton vicinal coupling constants in the heteroatomic moieties have been carried out. Modified Karplus type functions for the 3J(HH′) coupling constants have been found. These functions take into account the electronegativity and orientation of the α‐atoms. It is shown that the semi‐chair conformation of compounds of the cis series is characterized by a cyclic torsion angle ψ = 30° in accordance with both the experimental data and LCAO MO EHM calculations.