Curtin–Hammett principle

https://doi.org/10.1351/goldbook.C01480
In a @C01033@ that yields one product (X) from one conformational @I03289@ (A') and a different product (Y) from another conformational @I03289@ (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 @S06082@; it is controlled only by the difference in standard free energies (\(\unicode[Times]{x3B4} \Delta ^{\ddagger }G\)) of the respective @T06468@.
C01480-1.png
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 @E02177@) and the respective rate constants of their reactions; these parameters are generally — though not invariably — unknown. The diagram below represents the energetic situation for @T06446@ of interconverting isomers A and A' into products X and Y.
C01480.png
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1102 [Terms] [Paper]