Infra-red absorption spectra of some amino compounds

Abstract

An investigation of the infra-red absorption spectra of five amino compounds (glycine, diketopiperazine, tetramethyl-diketopiperazine, glycylglycine and urea) has been made in the region 2-8-3-6 μ . The substances were used in the form of thin crystalline layers deposited on quartz windows. The spectra are discussed with regard to the molecular structure of the compounds under consideration. The number and position of the N—H frequencies in glycine and glycyl-glycine are in agreement with the assumption that these two molecules are in the zwitterion form in the crystal. The close similarity between the spectra of diketopiperazine and tetramethyldiketopiperazine on the one hand, and the amino acids and urea on the other, proves that no lactam-lactim interchange occurs in diketopiperazine and its derivative. Both compounds are shown to possess a centre of symmetry. It follows from the experimental evidence that in all the substances investigated resonance between the C—N and 0 = 0 bonds takes place.