Question

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

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

Answer 1

The Correct Option is B

The question pertains to the dehydrohalogenation reaction of 2-Bromo pentane, resulting in the formation of Pent-2-ene as the major product. Among the given options, the correct principle governing this process is Saytzeff’s Rule. Let's understand why this is the case:

Explanation

1. Dehydrohalogenation Reaction: This is a type of elimination reaction where a hydrogen atom and a halogen atom are removed from adjacent carbon atoms, resulting in the formation of an alkene.
2. 2-Bromo Pentane Structure:
   • The structure of 2-bromo pentane is CH₃-CH₂-CHBr-CH₂-CH₃.
3. Saytzeff’s Rule: This rule states that during an elimination reaction, the more substituted alkene is formed as the major product. This is because more substituted alkenes are more stable due to hyperconjugation and inductive effects.
4. Formation of Pent-2-ene:
   • Applying Saytzeff’s rule to 2-bromo pentane, the removal of a β-hydrogen from the more substituted carbon leads to the formation of Pent-2-ene (CH₃-CH=CH-CH₂-CH₃), which is the more substituted, and therefore more stable, alkene.

Conclusion:

Among the options, Saytzeff’s Rule correctly predicts the major product in a dehydrohalogenation reaction resulting in a more substituted alkene, which aligns with the observed formation of Pent-2-ene from 2-bromo pentane. Therefore, the answer is Saytzeff’s Rule.

Elimination of Other Options:

• Huckel’s Rule: This rule is related to the aromaticity of compounds and is not relevant to the formation of alkenes through dehydrohalogenation.
• Hund’s Rule: This rule pertains to electron filling in orbitals and is not applicable to chemical reaction pathways.
• Hofmann Rule: This rule predicts the formation of the less substituted alkene as the major product, which is contrary to Saytzeff’s Rule and not applicable here.