Role of Charge Transfer in Nucleophilic Substitution Reactions in Clusters of 1-Fluoro-n-chlorobenzene Cations with Ammonia Molecules

Article abstract of DOI:10.1021/j100188a015

The reaction behavior of mixed clusters consisting of fluorochlorobenzene radical cations surrounded by ammonia molecules has been studied by resonant two-photon ionization.The spectral characterization of the neutral precursors allows one to study ion reactions in the cluster with a well-defined microsolvation environment.In addition to charge transfer, two types of nucleophilic substitution reactions take place.In a binary complex chlorine is ejected either in an ipso substitution by radical loss or, for meta and para isomers, by HCl formation, in the latter case by a metastable decay.The reaction efficiency for Cl elimination decreases with decreasing dipole moment of the chromophore.It is rationalized by a ? addition intermediate with an activation barrier due to charge transfer as postulated by the model of Shaik and Pross.The HCl elimination is not rate determined by the formation of a ? intermediate.In ternary and larger mixed complexes mainly substitution of fluorine takes place with HF as leaving group, corresponding to the onset of solvation catalysis.