Quantum Chemical Study of Hydroxyand Formyl-Substituted Benzenonium Ions1
Substituted benzenonium ions (protonated benzene derivatives) model the intermediates in electrophilic aromatic substitution reactions. This paper presents a quantum chemical study at the MP2/6-31G* level of the various cations that could result from mono-protonation of phenol and benzaldehyde. Five isomeric ions were investigated in each case, the four benzenonium ions resulting from protonation at an ortho, meta, para, or ipso position, and the ion resulting from protonation at the oxygen. The results show the effects of the hydroxy and formyl substituents on the relative energies of the isomeric benzenonium ions. Wiberg bond orders and Reed–Weinhold (NPA or natural) atomic charges are also reported.