Board-style MCQs and past-paper questions in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
Multiple-choice questions
Solved questions & self-assessment (past papers)
Explain why SN2 gives inversion but SN1 gives racemisation
In SN2 the nucleophile attacks from behind the leaving group in one step; the other three bonds flip through like an umbrella → inversion of configuration.
In SN1 the leaving group goes first to give a flat carbocation; the nucleophile then attacks either face equally → a 50:50 racemic mixture.
Why are aliphatic amines stronger bases than ammonia, but aniline is weaker?
Alkyl groups are electron-donating (+I), so they push electron density onto N → the lone pair is more available and the cation formed is more stable → aliphatic amine > NH₃.
In aniline the N lone pair is delocalised into the benzene ring by resonance, so it is far less available → aniline < NH₃.
2-bromobutane + hot alcoholic KOH — predict the major product (Saytzeff)
Hot alcoholic KOH causes elimination of HBr. Two alkenes are possible: but-1-ene and but-2-ene.
By Saytzeff's rule the more highly substituted (more stable) alkene dominates → major product is but-2-ene.