Ir spectra and conformational behavior of N-acetyl-(glycine,L-alanine,L-leucine)-N′-methylamides in chloroform

NH stretching bands of N-acetyl-(glycine, L -alanine, L -leucine)-N′-methylamides in dilute chloroform solution have shown that these dipeptides are present as a mixture of intramolecularly hydrogen-bonded five-membered ring species and nonhydrogen bonded species. Integrated absorption intensity measurements revealed that the concentration of the intramolecularly hydrogen bonded species decreased from 62% in glycine to 35% in the L -leucine derivatives.