Selected amino acid derivatives are investigated in order to obtain in
formation about their intramolecular interaction, using infrared spect
roscopy in the fundamental and overtone regions. A weak attractive int
eraction, responsible for the arrangement of the molecules in a five-m
embered ring, was found. Equilibrium constants for the intramolecular
association were determined, with values between five and two. The int
eraction enthalpy was found to be close to zero.