Abstract
Ab initio Density Functional Theory calculations are presented on cyclization and hydrogen abstraction reactions of various polycyclic aromatic hydrocarbons (PAH) which are important for numerous applications. Attention is focussed on the influence of the local structure of the cluster on the reactivity of these elementary radical processes. This is done by calculating the kinetic parameters by means of Transition State Theory. For ring-closure reactions the activation energies are largely affected by the local structure of the polycyclic aromatic hydrocarbon. The variations can be explained in terms of the aromaticity of the reactants and steric hindrance between the attacking radical and the substrate. The aromaticity of the various PAHs can be efficiently probed by various magnetic properties (proton chemical shifts, magnetic susceptibilities and nuclear-independent chemical shifts (NICS)). A correlation is found between the variations in aromaticity during a chemical reaction and the reaction barrier. Reaction barriers for hydrogen abstraction reactions are quite insensitive for the local PAH structure. Variations in the preexponential factor must be attributed to the presence of low vibrational internal rotations or various bending modes in the clusters.
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