Conformational study of N-vinyl-2-isopropyl- and N-vinyl-2-cyclopropylpyrroles by1H and13C NMR

In N-vinyl-2-isopropylpyrrole the isopropyl group is in a conformation with the CH₃ group in an anti position to the vinyl group. On introducing a substituent at the 3 position of the ring the isopropyl group passes into a gauche and (or) a syn conformation, leading to an increase in the dihedral angle between the plane of the vinyl group and the pyrrole ring. In N-vinyl-2-cyclo-propylpyrrole the cyclopropyl group is 80% in the gauche form, which is attributed to the repulsion between the electrons of the -shells of the cyclopropyl and pyrrole fragments.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1031–1038, May, 1991.