Identify the correct order of reactivity for the following compounds towards the S _ N 2 reaction: (I) (II) (III) CH ₃- CH ₂- Cl

Step-by-step solution

The reactivity of alkyl halides towards the S _ N 2 reaction depends on the steric hindrance and the stability of the transition state. In compound (I), 1-chloro-2-propanone (an -haloketone), the adjacent carbonyl group strongly stabilizes the S _ N 2 transition state through the overlap of its empty ^ * orbital with the partially filled p -orbital of the transition state. This makes it exceptionally reactive. In compound (II), 3-chloro-1-propene (an allylic halide), the adjacent C = C double bond also stabilizes t