The Energies and bond lengths of conjugated molecules. An introductory review of theoretical developments

Abstract

The concept of the π-type of bond, introduced originally to explain the rigidity of the double bond of ethylene, forms the basis of the theoretical treatment of many of the properties of organic molecules. It has led to extensive calculations of energy contents and so of ‘resonance’ energies. The percentage double-bond character and the lengths of carbon-carbon links have been deduced theoretically for a wide range of molecules and found to be in substantial agreement with X-ray measurements. Recently the theory has been developed to deal with the reactivities of conjugated molecules with promising results. The successes and limitations of the present state of the theory are reviewed.