The 13C nmr chemical shifts of benzyl 4-ethyl-3,5-dimethylpyrrole-2-carboxylate (1), methyl E-3-(3-ethyl-4,5-dimethylpyrrol-2-yl)-2-cyanopropenoate (2), and methyl E-3-(5-(benzyloxy)carbonyl-3-ethyl-4-methylpyrrol-2-yl)-2-cyanopropenoate (3) have been compared to their X-ray crystallographic structures. The 13C nmr chemical shifts were determined by direct comparison of a series of closely related homologs.Crystal data for 1, 2, and 3 are as follows: 1, monoclinic, P21/c, a = 14.934(2), b = 6.674(2), c = 15.269(2) Å, β = 101.96(1)°, Z = 4; 2, monoclinic, P21/n, a = 7.3030(3), b = 13.478(1), c = 12.985(1) Å, β = 97.48(1)°, Z = 4; 3, monoclinic, P21/c, a = 11.157(2), b = 13.109(2), c = 14.068(1) Å, β = 115.47(1)°, Z = 4. The structures were determined with diffractometer data by direct methods, and refined by full-matrix least-squares techniques to R = 0.052, 0.040, 0.038 for 862, 2032, 1483 reflexions, respectively. The molecules are approximately planar, except for deviations of the phenyl rings and of the terminal carbon atoms of the C3-ethyl groups from the molecular planes. The bond lengths in the pyrrole rings differ from those in pyrrole itself, as a result of the presence of the strongly electron-withdrawing sustituents; exocyclic bond lengths also exhibit differences from normal values.The competitive effects of the various electron withdrawing groups have been correlated to change in bond lengths, 13C chemical shifts, and the chemical reactions of the pyrrolic nucleus.