Molecular Orbital Theory for Organic Chemists

In 1931 Erich Hückel published his treatment of benzene with a method now generally referred to as the Hückel MO (HMO) method. He showed how cyclic arrays of 2, 6 and 10 π-electrons form closed shells that provide enhanced stability. By the middle thirties he had applied his approach to other aspects of organic chemistry but thereafter did no further original work. Extensive theoretical and experimental work on his concepts was done by others. "Molecular Orbital Theory for Organic Chemists" was written a quarter century later and documented brilliant syntheses of new "4n+2" molecules as well as numerous applications of HMO theory to redox processes, aromatic substitution, carbocation and carbanion reactions, rearrangements, as well as "Frontier Orbital" perturbation approaches. The period reviewed developed predominantly the chemistry of π-electrons but was followed shortly after by various treatments of σ-electrons in what can now be recognized as the next era of quantum chemistry.