Crystallographic studies in the pyrrole series. Part II. Crystal and molecular structure of 5,5′-diethoxycarbonyl-3,3′,4,4′-tetraethyldipyrrol-2-ylmethane
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 C2v 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 NH vectors, one syn and the other anti. The molecules are arranged in the crystal lattice as hydrogen-bonded, centrosymmetrically related dimers.