Comparison of the proton transfer path in hydrogen bonds from theoretical potential energy surfaces and the concept of conservation of bond order

The 'quantum-mechanically derived reaction coordinates' (QMRC) for the proton transfer in hydrogen bonds involving fluorine, oxygen and chlorine have been derived from earlier ab initio calculations of potential energy surfaces. A comparison is made between QMRC and the corresponding reaction coordinates (BORC) derived by applying the Pauling bond order concept together with the principle of conservation of bond order. Theoretical calculations have shown that the sum of the bond orders remains close to constant along the reaction coordinate in agreement with the Pauling postulate. The BORC correlation curves agree very well with theoretical results. The results indicate that the BORC curve gives a good representation of the reaction coordinates (proton transfer path) for any X-H---Y aggregate.