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

Abstract

The geminal coupling constant ²J_PNC 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 ²J_PNC in phosphoramidates is dependent on the conformation of the phosphoramide function. The ²J_syn constant is affected by the changes in the bulk of the N-alkyl group, with ²J_syn values successively increased on going from N-methyl to N-isopropyl.