The effects of substituents on the alkynes on reactivities in ruthenium catalyzed [2+2] cycloadditions have been studied using density functional theory. The theoretical studies predicted the same trends as observed in experiment. Substituents may affect the reactivities due to steric repulsions, electronic effects, and intramolecular hydrogen bonds. The effects of a remote substituent on the regioselectivity of cycloadditions of 2-substituted norbornenes with alkynes have been investigated. Theory predicted the same trends as experiment and matched the experimental product ratios well. The origin of the regioselectivities is attributed to the different strengths of the pi[right arrow][pi](C 2-Y) or pi[right arrow][sigma](C 2-Y) orbital interactions in 2-substituted norbornenes. Theoretical studies of the conformations and NMR properties of linear and branched perfluoro-octanesulfonamides (PFOSA) furnished qualitative explanations of the variable temperature 19F NMR spectra. The 19 F chemical shifts predicted by the B3LYP-GIAO method are in good agreement with experiment.