|Chapter 10: Conjugation in Alkadienes and Allylic Systems|
Kinetic and Thermodynamic Control
The potential outcome of a reaction is usually influenced by two factors:
|Consider the case where a starting material, SM,
can react to give two different products, P1 and P2 via
different pathways (represented by green and blue lines).
Reaction 1 via pathway 1 (green) generates P1.
Reaction 2 via pathway 2
(blue) generates P2.
1. At low temperature, the reaction preferentially proceeds along the green path to P1 and stops since they lack sufficient energy to reverse to SM, i.e. it is irreversible, so the product ratio of the reaction is dictated by the rates of formation of P1 and P2, k1: k2.
2. At some slightly higher temperature, reaction 1 will become reversible while reaction 2 remains irreversible. So although P1 may form initially, over time it will revert to SM and react to give the more stable P2.
3. At high temperature, both reaction 1 and 2 are reversible and the product ratio of the reaction is dictated by the equilibrium constants for P1 and P2, K1 : K2.
|© Dr. Ian Hunt, Department of Chemistry, University of Calgary|