55E - Organic Chemistry (Mcmurry)

Question

Although 2-substituted 2-cyclopentenones are in a base-catalyzed equilibrium with their 5-substituted 2-cyclopentenone isomers (Problem 22-55), the analogous isomerization is not observed for 2-substituted 2-cyclohexenones. Explain.

Step-by-Step Solution

Answer

The isomerization is not observed for 2-substituted 2-cyclohexenone because of the absence of acidic proton.

Step 1: Isomerisation

The chemical reaction in which the molecule's chemical structure varies just by the transfer of a double bond is called the isomerisation reaction. Enolisation is an example of isomerisation reaction.

Step 2: Determination of given compound

The given compound is,

2-methyl-2-cyclohexenone

 

The isomerisation of 2-substituted 2-cyclohexenone to a 6-substituted 2-cyclohexenone needs the removal of the proton from the 5^th position of the isomer.

The proton present in this position is not acidic. So, double bond isomerisation will not occur.