Coulson-Moffit model

A. The Coulson-Moffit and Walsh Models of the Molecular Orbitals of Cyclopropane 220... 

The Coulson-Moffit and Walsh models of the cyclopropane orbitals have been used since the 1940s but there has been some argument about which, if either, provides an adequate description of the facts. Walsh s model has been the more popular because it is perhaps easier in concept and also because it was believed that the models are equivalents, although it was pointed out that they were not at the very outset more recent studies have particularized the differencesS S. ... 

FIGURE 4. Showing how molecular orbitals of the Coulson-Moffit and the Walsh models are made up by the linear combination of atomic orbitals of Figure 3. For each model the upper trio of symmetry d and a l is antibonding and the lower is bonding... 

To explain the properties of cyclopropane, of the cyclopropyl group and of other three-membered rings in terms of their electronic structure, two models were proposed in 1947. One model, due to Walshpostulates for the three-membered ring of carbon atoms a set of three bonding, symmetry-adapted orbitals (scheme 74) based on tangential 2p AOs and radial sp AOs p = 1,2,3) centred at each of the three carbon atoms. The other model, proposed by Coulson and Moffit, describes the electronic structure of cyclopropane in terms of three bent banana EBOs (scheme 75), in analogy to an earlier proposal by Forster... 

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