Crystallographic studies in the pyrrole series. Part II. Crystal and molecular structure of 5,5′-diethoxycarbonyl-3,3′,4,4′-tetraethyldipyrrol-2-ylmethane

Abstract

Crystals of the title compound (III) are monoclinic, space group P2₁/c, with cell dimensions a= 8·655(2), b= 17·781(4), c= 15·465(4)Å and β= 102·70(2)°. The structure was solved by direct methods and refined by block-matrix least-squares techniques to R 0·0713 for 2711 observed reflections. The pyrrole rings are distorted from the C_2v symmetry of pyrrole, but the distortion is much less marked than that found earlier with 3-acetyl-5-ethoxycarbonyl-4-ethyl-2-methylpyrrole (I). The two carbonyl groups of (III) are arranged in different orientations with respect to the N⋯H vectors, one syn and the other anti. The molecules are arranged in the crystal lattice as hydrogen-bonded, centrosymmetrically related dimers.