Density functional theory (DFT) studies, at the B3LYP/6-31G(d,p) level employing both explicit and implicit solvent models, have been carried out towards quantitatively characterizing the formation mechanism of a series of pyridine and pyrrole derivatives from multi-substituted 1-cyano-l,3-butadienes and organolithium reagents.Results indicated that pyridine and pyrrole formations are multi-step processes, in which the rate-determining step is restricted to an enthalpy (free-energy) barrier of 18 kcal·mo1-1, as determined using the explicit two-solvent-molecule model (TSM).Both solvent (tetrahydrofuran or ether) and organolithium reagents are shown to play instrumental roles in affecting the pyridine:pyrrole product ratios.The TSM results seem more reasonable than the pure self-consistent reaction field (SCRF) polarizable continuum model (PCM) in characterizing the solvent effect of these formation reactions.