The role of proximity orientation in intramolecular proton transfer reactions

Using Becke three-parameter hybrid functional combined with the Lee, Yang, and Parr correlation functional, denoted B3LYP, at 6-31G (d,p) level 21 intramolecular proton transfer reactions were computed. The DFT calculation results revealed that the reaction rate (activation energy) is strongly dependent on the distance between the two reacting centers (rGM in the ground state and rTS in the transition state), and the hydrogen bonding angle (αGM) between them. Strong correlations were obtained between the activation energy, ΔG‡, values on one hand and rGM, rTS and αGM on the other hand. Correlation of calculated effective molarities (EM) with experimental EM values for certain intramolecular proton transfers demonstrates the strength of the DFT methods to predict reaction rate based on calculated geometrical parameters.