Conformational dependence of the circular dichroism of N-nitrosopyrrolidines

Abstract

Several suhstituted N-nitrosopyrrolidines were prepared and their chiroptical spectra studied. The circular dichroism of monocyclic compounds depends on substituents, solvents, and temperature changes. Some of these N-nitrosamines exhibit bisignate CD curves in the region of n-π * transition. On the contrary, conformationally restrictcd bi- and tricyclic compounds show monosignate Cotton effects, the magnitudes of which are almost solvent independent. Bisignate CD curves result from two half-chair conformers of the pyrrolidine ring being in equilibrium and contributing with the opposite CD signs. The Cotton effect signs can be predicted with our «lowered symmetry» sector rule developcd earlier