Conformational Analysis of <i>N</i>-Alkyl-<i>N</i>-[2-(diphenylphosphoryl)ethyl]amides of Diphenylphosphorylacetic Acid: Dipole Moments, IR Spectroscopy, DFT Study

• Main Authors: Anastasiia Kuznetsova, Denis Chachkov, Oleg Artyushin, Natalia Bondarenko, Yana Vereshchagina
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Molecules
• Subjects: carbamoylphosphine oxides; phosphorylated acetamides; dipole moments; conformational analysis; DFT calculations
• Online Access: https://www.mdpi.com/1420-3049/26/16/4832

Experimental and theoretical conformational analysis of <i>N</i>-methyl-<i>N</i>-[2-(diphenylphosphoryl)ethyl]diphenylphosphorylacetamide, <i>N</i>-butyl-<i>N</i>-[2-(diphenylphosphoryl)ethyl]diphenylphosphorylacetamide, and <i>N</i>-octyl-<i>N</i>-[2-(diphenylphosphoryl)ethyl]diphenylphosphorylacetamide was carried out by the methods of dipole moments, IR spectroscopy, and Density Functional Theory (DFT) B3PW91/6-311++G(df,p) calculations. In solution, these <i>N</i>,<i>N</i>-dialkyl substituted bisphosphorylated acetamides exist as a conformational equilibrium of several forms divided into two groups—with <i>Z</i>- or <i>E</i>-configuration of the carbonyl group and alkyl substituent, and <i>syn</i> or <i>anti</i> arrangement of the phosphoryl-containing fragments relative to the amide plane. The substituents at the phosphorus atoms have eclipsed <i>cis</i>- or staggered <i>gauche</i>-orientation relative to the P=O groups, and <i>cis</i> orientation of the substituents is due to the presence of intramolecular H-contacts P=O...H−C_phenyl or p,π conjugation between the phosphoryl group and the phenyl ring. Preferred conformers of acetamides molecules are additionally stabilized by various intramolecular hydrogen contacts with the participation of oxygen atoms of the P=O or C=O groups and hydrogen atoms of the methylene and ethylene bridges, alkyl substituents, and phenyl rings. However, steric factors, such as a flat amide fragment, the bulky phenyl groups, and the configuration of alkyl bridges, make a significant contribution to the realization of preferred conformers.