Facioselectivity Facioaselectivity, Faciononselectivity, Stereofacioselectivity

Facioselectivity characterizes the preferential reaction at molecular face 1 (top) as opposed to reaction at paired face 2 (bottom). A reaction is said to he facioaselective if (a) every pathway (transition state) involved in the reaction at face 1 has an isoenergetic coimterpart a t face 2, and (b) both transition states of every isoenergetic pair are homomorphic. Quartets ql,q2 represent facioaselective transformations. Operationally, in an facioaselective transformation, the product(s) obtained from face 1 will be exactly identical (in structure and relative amounts) with that(those) obtained from face 2. 

It is to be noted that we deal here with paired faces. There may be selectivity also between faces that are not paired, i.e. nonstereofaces, that belong to different planar moieties within the same molecule or different molecules. Such selectivity would be nonstereofacioselectivity which may reduce to nonstereofacioaselectivity, or nonstereofaciononselectivity. We will not deal with these. 

The quantitative expressions for facioselectivity for the three subclasses are as follows  

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To clarify selectivity at faces of planar molecular fragments, or facioselectivity, we presented a complete classification of all eleven types of stereotopic molecular faces. W e defined the different modes of facioselectivity viz. facioaselectivity, faciononselectivity and stereofacioselectivity at each type of molecular face. We also discussed difacioselectivity for conjunctive processes involving the interactions of two molecular faces. 

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