INFRARED MATRIX-ISOLATION STUDIES OF AMINO-ACIDS - MOLECULAR-STRUCTURE OF PROLINE

IR spectra of proline and deuteroproline isolated in low temperature A r matrixes have been obtained. It is shown that in the isolated state proline exists in the molecular form. The spectra are interpreted usin g normal coordinate analysis. It is found that band splitting in the s pectra is caused by the occurrence of two proline conformations. The s tructures of these conformations differ in the position of the COOH gr oup with respect to pyrrolidine ring. The conformations are found to b e stabilized by the intramolecular hydrogen bond. It has been shown th at conformational equilibrium results in the splitting of most bands i n the IR spectra of proline and deuteroproline. This splitting is maxi mal for C=O stretching bands (23 cm-1). The structure and relative ene rgies of the conformations are determined by the AM1 quantum chemical method.