Question

Propose an arrow-pushing mechanism for the reaction below. 1. Cl₂, H₂O 2. Nah

Answer 1

This reaction is chlorhydrins formation followed by intramolecular S2 reaction Mechanism Step 1: Addition of chlorine molecule across double bond of but l-ene to form 3 membered ring containing positively charged chlorine Step II: This reaction is carried out in presence of a nucleophilic solvent i.e. Ho which attacks the ring from back side to form chlorohydrins SH OH Step III: The base NaH deprotonates the alcohol forming an alkoxide intermediate leads to an intramolecular SN2 reaction. The back side attack of alkoxide ion on carbon having chlorine forms epoxide oghe epoxide