Stereochemical dependence of 2 J PNC coupling constants in N-dialkyloxyphosphoryl amino acids and other phosphoramidate compounds

The geminal coupling constant 2JPNC in N- Dialkyloxyphosphorylamino acids and other phosphoramidate compounds is found to be small ( < 1 Hz) in the secondary amides (1)–(5) and (9)–(6) and larger (2 8–7.1 Hz) in the tertiary amides (6)–(8) and (17)–(20). IR studies on the secondary amides show that in solution these compounds favour the conformation in which the N–C bond is anti to PO bond. The two-bond coupling constant 2JPNC in phosphoramidates is dependent on the conformation of the phosphoramide function. The 2Jsyn constant is affected by the changes in the bulk of the N-alkyl group, with 2Jsyn values successively increased on going from N-methyl to N-isopropyl.