A theoretical and topological study on the electroreduction of chlorobenzene derivatives

Abstract

The electrochemical behaviour of 12 polychlorobenzene derivatives is discussed on the basis of calculated quantum-mechanical indexes (CNDO/2, MNDO, AM1 methods) and of pure structural parameters reckoned by means of graph theory (Wierner, Balaban, Randic, PID and W_rms numbers). Even the existence of good relationships between reduction potentials and energies of virtual molecular orbitals, π* or σ*(closed-shell calculations), does not account for the details of the electron uptake at the molecular level. Open-shell calculations (MNDO) regarding unrelaxed radical anions are much more promising in this respect, the occurrence of the so-called ‘ortho effect’ can be so justified. The reductive process (at least in the experimental conditions considered here) is shown to be scarcely affected by solvent-shell or internal molecular rearrangements; this view is supported by the good description of the process, strictly on structural grounds regarding the whole of the molecule, provided by the graph-theoretical indexes.