Minimal steric interaction principle

For acyclic fragments and molecules, the principle of longest pathways has been implemented in CORINA (sec Figure 2-95) i.e., since no ch configuration is specified, all torsions arc set to anti in order to minimize steric interactions. 

MSI principle The principle of minimal steric interaction which states that the preferred conformation of a group is that which results in the smallest possible steric effect. 

The Minimal Sterlo iHteraotlon(MSl) Principle. As all sterlo Interactions result In an Increase In the energy of a system, the observed steric effect In the system will be the smallest possible. Thus, when the sterlo effect of a group X depends on Its oonfoiMnatlon, the group will prefer that conformation which results In the smallest possible steric Interaction. This Is the MSI principle. 

Using the VO(acac)2-Bu OOH method, highly stereoselective epoxidations of acyclic homoallylic alcohols are possible. Stereoselectivity in a predictable manner has been demonstrated using a detailed transition-state model in which a chair-like conformation is adopted wherein the steric interactions of the various substituents are minimized according to accepted principles of conformational analysis. For example, the homoallylic alcohol (3) affords the epoxide (4) in greater than 400 1 selectivity via the transition-state model shown in Scheme 5. 

In a diatomic molecule it is of benefit to minimize the steric influence of those valence electrons not directly involved in mediating the interatomic interaction. The competing factors in this case are atomic size, interatomic distance, distribution of valence-electron density and the Pauli principle. 

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