NEETChemistryHaloalkanes and Haloarenes
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Dehydrohalogenation of 2-bromo-3-methylbutane with alcoholic KOH gives 2-methylbut-2-ene as the major product. Reason (R): The reaction proceeds via an E1 mechanism involving a carbocation intermediate. In the light of the above statements, choose the most appropriate answer from the options given
Options
- ABoth (A) and (R) are correct and (R) is the correct explanation of (A)
- BBoth (A) and (R) are correct but (R) is not the correct explanation of (A)
- C(A) is correct but (R) is not correct
- D(A) is not correct but (R) is correct
Correct answer
C. (A) is correct but (R) is not correct
Step-by-step solution
Assertion (A) is correct. When 2-bromo-3-methylbutane ( CH ₃- CH ( CH ₃)- CH ( Br )- CH ₃ ) is treated with alcoholic KOH, it undergoes beta-elimination. According to Zaitsev's rule, the hydrogen is preferentially removed from the beta-carbon with fewer hydrogen atoms to yield the more highly substituted alkene. Removal of hydrogen from C3 gives 2-methylbut-2-ene (a trisubstituted alkene), which is the major product. Reason (R) is incorrect. Alcoholic KOH is a strong base, which promotes a concerted E2 (bimolecular