The effective molarity (EM) puzzle in proton transfer reactions

The DFT and HF calculation results for the proton transfer reactions of three different systems reveal that the reaction mechanism (transfer of a proton to a nucleophile) is largely determined by the distance between the two reactive centers (r). s with relatively large r values tend to abstract a proton from a molecule of water, whereas, these with a relatively small r values prefer to be engaged intramolecularly and their interaction with water is only via hydrogen bonding. Further, the results indicate that the effective molarity (log EM) for an intramolecular process is strongly correlated with the distance between the two reacting centers (r) in accordance with Menger’s “spatiotemporal hypothesis”.