Question

explain the relative reactivities of allyl halides vs vinyl halides and aryl halides

Answer 1

Aryl halides are relatively unreactive toward nucleophilic substitution reactions. This lack of reactivity is due to several factors. ... In addition, the carbon‐halogen bond is shorter and therefore stronger in aryl halides than in alkyl halides. The carbon‐halogen bond is shortened in aryl halides for two reasons.

Answer 2

The relative reactivity of allyl halides vs vinyl halides and aryl halides is$\[Allyl\,halides > Vinyl\,halides > Aryl\,halides\]$

Explanation:

• Allyl halides are those compounds in which the halogen atom is attached to the $\[s{p^3}\]$-hybridised carbon atom which is adjacent to a $\[C = C\]$ bond.
• Vinyl halides are those compounds in which the halogen atom is attached to the $\[s{p^2}\]$-hybridised carbon atom of a $\[C = C\]$ bond.

• Aryl halides are those compounds in which which the halogen atom is attached to the $\[s{p^2}\]$-hybridised carbon atom of an aromatic ring.
• The halogen atom bonded to the $\[s{p^3}\]$-hybridised carbon atom can be cleaved easily. Therefore, allyl halides are more reactive.
• The halogen atom bonded to the $\[s{p^2}\]$-hybridised carbon atom has a partial double bond character because of resonance and therefore, it is strongly bonded. So, it is not easy to cleave it. Thus, vinyl halides are less reactive than allyl halides.
• The halogen atom bonded to the $\[s{p^2}\]$-hybridised carbon atom cannot be cleaved easily due to the delocalisation and resonance.
• The resonance in the aromatic ring is more than in the vinyl compounds. Thus, the aryl halides are even less reactive than vinyl halides.
• Thus, the order of reactivity can be given as: $\[Allyl\,halides > Vinyl\,halides > Aryl\,halides\]$

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