Question

The major product formed in dehydrohalogenation reaction of $2-Bromo$ pentane is $Pent-2-ene$. This product formation is based on ?

• A. Saytzeff's Rule
• B. Hund’s Rule
• C. Hofmann Rule
• D. Huckel’s Rule

Answer 1

The Correct Option is A

The question pertains to the product formation in a dehydrohalogenation reaction of 2-Bromo pentane. The correct answer is based on Saytzeff's Rule. Let's explore this further:

Dehydrohalogenation is a chemical reaction that involves the removal of a hydrogen halide (in this case, HBr) from an alkyl halide, leading to the formation of an alkene.

2-Bromo pentane, when subjected to dehydrohalogenation, undergoes an elimination reaction to form an alkene as a product. In this reaction, the specificity of the product formation is explained by Saytzeff's Rule, which can be stated as follows:

Saytzeff's Rule: In the elimination reactions, the preferred formation of alkenes is such that the more substituted alkene (the one with more alkyl groups attached to the double-bonded carbon atoms) is the favored product.

Applying Saytzeff's Rule to 2-Bromo pentane:

• The removal of HBr from 2-Bromo pentane can potentially form two different alkenes: Pent-1-ene and Pent-2-ene.
• Pent-2-ene, being more substituted compared to Pent-1-ene, is the major product formed in accordance with Saytzeff's Rule.

Let's briefly discuss why the other options are incorrect:

• Hund’s Rule: Relates to electron configuration in orbitals and has no relevance to chemical elimination reactions.
• Hofmann Rule: Describes scenarios where the less substituted alkene is the major product, generally occurring with bulky bases. This contradicts the formation of Pent-2-ene as the major product here.
• Huckel’s Rule: Concerns the aromaticity of compounds and is unrelated to alkene formation in this context.

Thus, the formation of Pent-2-ene in the dehydrohalogenation of 2-Bromo pentane is indeed governed by Saytzeff's Rule.