Nuclear magnetic resonance spectroscopy. Carbon-carbon coupling in cyclopropane derivatives

The nature of the bonding in cyclopropane, the smallest and most highly strained carbocyclic ring system, has long been a lively and controversial topic. Walsh has described the carbon-carbon bonding in cyclopropane as involving a three-center bond, while Coulson and Moffitt and Trinajstić and used quantum-mechanical treatments equivalent to bent bonds wherein the regions of highest electron density are not located along the C-C internuclear axes. Molecular orbital calculations of varying degrees of sophistication have been carried outs A recent summary of the description of bonding in cyclopropanes was given by Bernett.