Question

Elimination reaction of 2-Bromo pentane to form pent-2-ene is :

• A. β-Elimination reaction
• B. Follows Zaitsev rule
• C. Dehydrohalogenation reaction
• D. Dehydration reaction

Answer 1

The Correct Option is A

The elimination reaction of 2-Bromo pentane to form pent-2-ene involves the loss of a bromine atom (a halide) and a hydrogen atom from adjacent carbon atoms in the molecule. This process is known as a β-elimination reaction. Let us explore and understand the underlying chemistry step-by-step:

1. Concept of β-Elimination Reaction:
   • In organic chemistry, a β-elimination reaction involves the removal of two substituents from a molecule. Specifically, a hydrogen atom and a halogen atom or other leaving group are removed from adjacent carbon atoms.
   • For 2-Bromo pentane, when a base is added, it abstracts a hydrogen from the β-carbon (the carbon next to the carbon holding the leaving group, bromine in this case).
   • This leads to the formation of an alkene, in this case, pent-2-ene.
2. Zaitsev's Rule:
   • This rule states that in an elimination reaction, the more substituted alkene is generally favored. For 2-Bromo pentane, this applies because pent-2-ene is formed, which is the more substituted and hence the more stable product.
   • However, the question specifically asks for the type of reaction, and while Zaitsev's rule supports the formation of pent-2-ene, it is not the primary characterization of the reaction.
3. Dehydrohalogenation Reaction:
   • This is another term for the β-elimination reaction when the leaving group is a halogen, as in the case of 2-Bromo pentane. The reaction involves the removal of a hydrogen and a halogen (bromo) resulting in an alkene.
   • Thus, β-Elimination and Dehydrohalogenation effectively describe the same type of reaction in this context.
4. Dehydration Reaction:
   • This involves the removal of a water molecule (H₂O) from an alcohol to form an alkene. The term does not apply here since we are dealing with the removal of a hydrogen and a bromine atom, not water.

Conclusion:

Among the given options, the most appropriate designation for the elimination reaction of 2-Bromo pentane to form pent-2-ene is a \beta-Elimination reaction. This is characterized by the removal of the bromine atom and a β-hydrogen atom leading to the formation of an alkene, specifically pent-2-ene.