The Infrared Spectra of N-Acetylglycine and Diketopiperazine in Polarized Radiation at 25° and at −185°C

The infrared absorption spectra of single crystals of N-acetylglycine and of diketopiperazine have been observed at room temperature, and at −185°C, using polarized radiation. The spectrum of the former substance shows some remarkable changes with temperature. In both cases cooling produces a pronounced narrowing of the broad bands due to the vibration of hydrogen atoms involved in strong hydrogen bonds. The two spectra furnish examples of NH absorption in the two extremes of weak and very strong hydrogen bonding. In diketopiperazine two possible interpretations of the doublet structure in the NH valence band are offered