Figure 7.4. Kinetic and Thermodynamic Enolates
The kinetic enolate forms more quickly, but is less stable than the thermodynamic enolate.Each of these two products is favored by different conditions. The kinetic product is favored in
reactions that are rapid, irreversible, at lower temperatures, and with a strong, sterically hindered
base. If the reaction is reversible, the kinetic product can revert to the original reactant and react
again to form the thermodynamic product. The thermodynamic product is favored with higher
temperatures; slow, reversible reactions; and weaker, smaller bases.
ENAMINES
Just as enols are tautomers of carbonyls, enamines are tautomers of imines. An imine is a
compound that contains a C=N bond. The nitrogen in the imine may or may not be bonded to an
alkyl group or other substituent. Through tautomerization (movement of a hydrogen and a double
bond), imines can be converted into enamines, as shown in Figure 7.5.
Figure 7.5. Enamination (Tautomerization)
On the right is the imine form, which is thermodynamically favored over the enamine form on the left.MCAT Concept Check 7.2:
Before you move on, assess your understanding of the material with these questions.