Calculation of High Pressure Effects in Reactions of Hydrogen Transfer from Substituted Toluenes to Bromine Atom

A given reaction may proceed through several different mechanisms, each with its own transition state (TS). These TSs may have similar energies but different geometries and, as a result, different volumes. According to transition state theory, the activation volume ($\Delta $V$^{\ne })$ is the difference between the volume of the TS and the reactants. Experimentally, activation volumes can be obtained from the pressure dependences of the rate constants: \begin{center} -RT($\partial $ln k/$\partial $P)$_{T}=\Delta $V$^{\ne }=$ V$^{\ne }$ - V$^{R}$ \end{center} By comparing the calculated and experimental activation volumes, one can pick a TS of the right ``size'' and thus elucidate the reaction mechanism by identifying the most likely reaction pathway. It has recently been shown by our research group that molecular dynamics simulations provide a suitable tool for theoretical calculations of activation volumes. In this project we focus on the calculation of the activation volumes for a series of reactions in which an alpha-hydrogen is abstracted from a substituted aromatic hydrocarbon by bromine radical.