The Question is from neet-chemistry organic-chemistry-basics types-of-reactions, and it was created by the author A.RAMA NAGESWARARAO

Question

The reaction of 2-bromobutane with alcoholic KOH predominantly follows which mechanism, and what is the major product?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Elimination reactions (E1 and E2) and Substitution reactions (SN1 and SN2)
 **Related Topics**: Reaction mechanisms, alkyl halides, strong bases, stereochemistry
 **Prerequisites**: Understanding of nucleophilic substitution and elimination reactions, understanding of carbocation stability.
## SOLUTION PATHWAY
**Given Information**:
  Reactant: 2-bromobutane
  Reagent: Alcoholic KOH (a strong base and a poor nucleophile in alcoholic solution)
  Condition: Alcoholic solution (favors elimination)
**Method & Steps**:
 1. Identify the type of alkyl halide and reagent.
  Reasoning: 2-bromobutane is a secondary alkyl halide. Alcoholic KOH is a strong base, but a poor nucleophile in alcoholic solution.
 2. Determine the predominant mechanism.
  Working: Since we have a secondary alkyl halide and a strong base in alcoholic solution, the E2 mechanism is favored over SN2.  E1 is less likely because E2 is faster with a strong base.
  Key Point:  Alcoholic KOH favors elimination over substitution.  The strong base abstracts a proton, leading to elimination.
 3. Predict the major product.
  Result: The E2 mechanism will lead to the formation of an alkene.  The most substituted alkene (Saytzeff's rule) is the major product. In this case, 2-butene is the major product.
  Verification:  The E2 mechanism involves a concerted reaction where the base removes a proton and the leaving group departs simultaneously. This leads to the formation of a double bond.
 ## OPTION ANALYSIS
A :x: E1 reactions require a carbocation intermediate which is not favored in the presence of a strong base.  Even if E1 occurred, the major product would still be 2-butene (Saytzeff's rule).
B ✓: This option correctly identifies the E2 mechanism and the major product, 2-butene. The strong base and secondary halide favor this mechanism.
 C :x: SN1 reactions require a carbocation intermediate, which is not favored in the presence of a strong base.  Alcoholic KOH would favor elimination.
D :x: SN2 reactions are unlikely with a strong base.  Moreover, SN2 reactions would lead to an alcohol, not an alkene.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing E1 and E2 mechanisms: Remember that E1 involves a two-step process with a carbocation intermediate, while E2 is a concerted one-step process.
  2.Ignoring Saytzeff's rule:  The most substituted alkene is usually the major product in elimination reactions.
 **Quick Tips**:
  1.If a strong base is used with a secondary or tertiary alkyl halide, consider E2 as the dominant mechanism. 
  2.Remember Saytzeff's rule: More substituted alkenes are more stable and therefore favored.

A.RAMA NAGESWARARAO · Answer

E1; 1-butene

A.RAMA NAGESWARARAO · Answer

The correct Option is "E2; 2-butene"

A.RAMA NAGESWARARAO · Answer

SN1; 2-butanol

A.RAMA NAGESWARARAO · Answer

SN2; 1-butanol

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