Cornforth model

There is evidence to suggest that competing dipole effects will alter the preferred conformation. Thus, for example, halogens will prefer a conformation in which the dipoles are anti to one another. This is often described as the Cornforth model In this model the highly polarized group will take the place of the L-group of the Cram model. 

The Evans electrostatic model for 1,2-asymmetric induction incorporates Dunitz-Biirgi attack and torsional effects into the Cornforth model ... 

Figure 6-3. The Cornforth model for nucleophilic attack at acyclic carbonyl compounds containing a polar group.

If the hetero substituent is a nonchelating but polar substituent, the stereochemical outcome can be rationalized by the Cornforth model, in which the polar substituent and the carbonyl group assume an energetically favorable antiperiplanar conformation141. 

Cornforth model for nucleophilic addition to an a-chiral aldehyde. Note that Cl and O are anti-co-planar. 

The Felkin-Ahn model (shown here) and the Cornforth model (not shown here) both predict the stereochemical course of the epoxide formation. This is Et k i an early example of an applica- /... 

Discuss the factors behind selection of the reactive conformation in the Felkin-Ahn model for conversion of 53 to 54. How would Cornforth have rationalized this stereochemical result [For an interesting system where the Cornforth and Felkin-Ahn models predict different stereochemical results see Evans, D. A. Siska, S. J. Cee, V. J. Resurrecting the Cornforth Model for Carbonyl Addition Studies on the Origin of 1,2-Asymmetric Induction in Enolate Additions to Heteroatom-Substituted Aldehydes Andrew. Chem. Int. Ed. 2003, 42, 1761-1765] (CJH-5)... 

---