ELECTRON-TRANSFER AND ION-PAIRING .29. MNDO CALCULATIONS AS A VALUABLE TOOL FOR STRUCTURE EVALUATION OF CONTACT ION-PAIRS

Contact ion pairs, essential intermediates of both chemical and biochemical reactions in solution, can be satisfactorily approximated by MNDO calculations as exemplified by the lithium and potassium salts of 2,5-trimethylsilyl-p-benzosemiquinone radical anion and by sodium tetraphenylallyl anion diethyl ether. Topics discussed are the structural changes of p-benzoquinone derivatives on single-electron reduction, the dynamics of the countercations in semiquinone radical contact ion pairs measured by temperature-dependent ESR spectra, as well as structural details of the sodium tetraphenyl-allylanion complex isolated such as its intramolecular Na dibenzene sandwich or its diethylether solvation.