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 Wrms 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.