Structure of N,N-Dialkylamides of Diphenylphosphorylacetic Acid in Solution: Dipole Moments, IR Spectroscopy, and Quantum-Chemical Study

Conformational analysis of N,N-dialkylamides of diphenylphosphorylacetic acid has been carried out using the methods of dipole moments, IR spectroscopy, and quantum chemistry DFT B3PW91/6-311++G(df,p), including the CPCM model. In solution, N,N-diethyl-, N,N-dibutyl- and N,N-dioctylamides exist as equilibrium mixture of conformers, in which forms with cis-orientation of phenyl rings and synclinal orientation of the C_sp3‒C_sp2_(C=O) bond relative to the phosphoryl group predominate, the carbonyl group and P‒C_sp3 bond being anticlinal. The stabilization of the preferred conformers is facilitated by intramolecular hydrogen contacts and the possible presence of the p,π-conjugation between the phosphoryl group and the phenyl ring in their molecules.