The Normal Vibrations of Diketopiperazine and Its N-Deuterated Compound

Abstract
The normal vibrations of diketopiperazine and its N-deuterated compound have been calculated, with the metylene groups treated as mass points. An assignment of the infrared absorption bands has been made on the basis of the calculated frequencies and potential energy distributions, and the nature of the characteristic vibrations of the cis-amide group has been discussed.