CONFORMATIONAL ASPECTS OF POLYPEPTIDE STRUCTURE .30. ROTATORY PROPERTIES OF CYCLIC AND BICYCLIC AMIDES . RESTRICTED AND RIGID MODEL COMPOUNDS FOR PEPTIDE CHROMOPHORES

The optical properties of monocyclic and bicyclic amides have been examined by optical rotatory dispersion (ORD) and circular dichroism (CD) techniques. The signs of the rotational strength of the n-7r* transitions of L-α-aminocaprolactam and L-pyrrolid-2-one-5-carboxyIic acid are interpreted in terms of both quadrant and octant rules. The effect of charged side-chain groups on the amide chromophores is also discussed. In addition to n-π* and π-π* Cotton effects, a third band in the spectra of bicyclic lactams has been observed. Infrared and circular dichroism dilution studies demonstrate that this Cotton effect arises from association of the lactams to form dimers. We have also been able to separate solvent and conformational effects on the ORD and CD spectra for the completely rigid bicyclic amides since alterations in conformation for these compounds can not occur. © 1969, American Chemical Society. All rights reserved.