Dehydration of 2-methyl-2 pentanol forms one major and one minor organic product. Draw the structures of the two organic products of this reaction
The Correct Answer and Explanation is :
The dehydration of 2-methyl-2-pentanol involves the elimination of a water molecule (H₂O) from the alcohol, resulting in the formation of an alkene. The reaction occurs under acidic conditions, typically using sulfuric acid or phosphoric acid, which promotes the loss of a hydroxyl group (-OH) and a hydrogen atom from adjacent carbon atoms. The two major types of products that can form are based on the position of the double bond after the elimination process.
Organic Products:
- Major product: 2-methyl-2-pentene
- Minor product: 3-methyl-1-butene
Explanation:
- Reaction Mechanism: The dehydration of 2-methyl-2-pentanol proceeds through an E1 elimination mechanism. The first step involves the protonation of the hydroxyl group, converting it into a better leaving group (water). Once water leaves, a carbocation is formed at the more stable carbon (the one adjacent to the initial hydroxyl group). The positive charge can stabilize on the carbon bearing the larger alkyl group (due to inductive and hyperconjugation effects).
- Major Product:
- In this case, the carbocation forms at the tertiary carbon (C-2) when the water leaves. This carbocation is highly stable due to the hyperconjugation and inductive effects of the surrounding methyl groups.
- The double bond forms between C-2 and C-3, leading to 2-methyl-2-pentene as the major product. This is because this alkene is more stable due to its substitution pattern.
- Minor Product:
- The minor product, 3-methyl-1-butene, arises when a hydride shift occurs from the C-3 to the C-2 position, leading to the formation of a secondary carbocation at C-1 (the carbon adjacent to the hydroxyl group).
- The double bond forms between C-1 and C-2, producing 3-methyl-1-butene. This product is less stable compared to 2-methyl-2-pentene and thus is formed in smaller amounts.
Structures:
- Major product: 2-methyl-2-pentene (CH₃C=CH-CH₂CH₃)
- Minor product: 3-methyl-1-butene (CH₂=CH-CH₂CH₃)
The E1 mechanism and the stability of the carbocation intermediates determine the formation of these products, with the more stable alkene being favored.