What is the structure of the major product in the reaction of methylcyclopentene with H2O?

In the reaction between methylcyclopentene and water (H₂O), the major product formed is 1-methylcyclopentanol. This reaction is typically an acid-catalyzed hydration process where water adds across the double bond of the alkene.

Here’s how the mechanism works: The double bond in methylcyclopentene acts as a nucleophile and reacts with the hydrogen ion (H⁺) from the acid, leading to the formation of a carbocation. Because the methyl group attached to the cyclopentene ring is able to stabilize the positive charge, the carbocation formed is a more stable tertiary or secondary carbocation depending on the position of the hydrogen bond addition. Subsequently, water can act as a nucleophile and attack the carbocation, leading to the formation of the alcohol.

To illustrate this, here’s a simplified structure of the major product:

          OH
           |
      CH3-C
        /     \
      C       C
      |         \
      C         C
       \       /
        C---C

In this structure, the hydroxyl (OH) group is added to the carbon where the double bond was present, resulting in the formation of 1-methylcyclopentanol as the major product of the reaction.