JEE Main levelSingle correct optionDifficulty 2 of 3o4195
Why does alcoholic KOH favour elimination from 2-bromopropane whereas aqueous KOH gives mainly propan-2-ol?
AEthanol is a better leaving group than water
BAlcoholic KOH contains ethoxide, a stronger and less solvated base, which abstracts a beta-hydrogen; in water, hydroxide is heavily solvated and acts mainly as a nucleophile
CEthanol stabilises the carbocation and so promotes E1
DKOH is insoluble in water and so cannot react there
Answer: B
In ethanol, the equilibrium OHX−+CX2HX5OHCX2HX5OX−+HX2O supplies ethoxide, a stronger base, and the medium is less solvating, so the base abstracts a proton (E2). In water, hydrated hydroxide favours substitution to propan-2-ol.