In a @[email protected] that yields one product (X) from one conformational @[email protected] (A') and a different product (Y) from another conformational @[email protected] (A'') (and provided these two isomers are rapidly interconvertible relative to the rate of product formation, whereas the products do not undergo interconversion) the product composition is not in direct proportion to the relative concentrations of the conformational isomers in the @[email protected]; it is controlled only by the difference in standard free energies (\(\unicode[Times]{x3B4} \Delta ^{\ddagger }G\)) of the respective @[email protected] It is also true that the product composition is formally related to the relative concentrations of the conformational isomers A' and A'' (i.e. the conformational @[email protected]) and the respective rate constants of their reactions; these parameters are generally — though not invariably — unknown. The diagram below represents the energetic situation for @[email protected] of interconverting isomers A and A' into products X and Y.