A general equation correlating intramolecular rates with ‘attack’ parameters: distance and angle

Using density functional theory (DFT) at the B3LYP level with the 6-31G(d,p) basis set, a general equation is derived relating activation energy with the distance between the two reactive centers (r_GM), and the hydrogen-bonding angle (α_GM) in an intramolecular proton transfer process. The strong correlation between the values of r_GM and α_GM with the activation energy, ΔG^‡, which reflects the experimental reaction rate, provides an excellent tool to predict reaction rate based on calculated geometrical parameters for a certain system (ΔH^‡, ΔG^‡ vs r_GM and α_GM). The slope of the equation can be used as an indicator of the mode by which the two reacting centers orchestrate in an intramolecular process.