Protonation in Benzyl Alcohol: Different Proton Affinities, Same Neutral Molecule

ABSTRACT

Background and Objectives: Benzyl Alcohol (BA) has 6 possible protonated sites which give rise to 6 possible proton affinities for the same neutral molecule (BA). However, experimentally, only one proton affinity value is reported for BA but computationally, each possible protonated site can be specifically optimized and the proton affinity calculated for each protonated species. Materials and Methods: In this study, quantum chemical calculations were carried out using GAUSSIAN 09 suite of programs. Five (5) different computational methods have been employed to calculate the proton affinity for each possible protonated analogue. Results: The results obtained are compared with the experimental value in order to determine the protonated analogue that corresponds to the experimental value and which is thermodynamically more favored. It was found that the best site for the protonation of BA is via the C ₇ atom as it corresponds more to the experimental value and also found to be more stable. Conclusion: Generally, the best computational methods for the calculation of the PA values of BA was observed to be B3LYP/6-311++G** but on the basis of the best site of protonation G ₄ method happened to be the best computational method.