Answers

 Here are the answers and explanations to the questions based on Haloalkanes and Haloarenes:

1. What is the difference between an alkyl halide and an allyl halide?

Alkyl halide: In alkyl halides, a halogen atom (X) is attached to an sp³-hybridized carbon atom. The general formula is R-X, where R is an alkyl group. Example: CH₃CH₂Cl (Ethyl chloride).

Allyl halide: In allyl halides, the halogen is attached to an sp³-hybridized carbon atom that is adjacent to a double bond (C=C). The general formula is CH₂=CH-CH₂-X. Example: CH₂=CHCH₂Cl (Allyl chloride).

Explanation: The key difference is the presence of a double bond near the halogen in allyl halides, which affects the reactivity and resonance stability. Allyl halides exhibit resonance stabilization, unlike alkyl halides.

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2. What are the reactivity differences between benzyl halides and benzylic halides in nucleophilic substitution reactions?

Benzyl halides: In benzyl halides, the halogen is attached to a carbon atom that is directly bonded to a benzene ring (C₆H₅CH₂-X). These compounds are highly reactive in nucleophilic substitution reactions (SN1 and SN2) due to the stabilization of the benzyl carbocation by resonance.

Benzylic halides: In benzylic halides, the halogen is attached to a benzylic carbon that is adjacent to a benzene ring, but the reactivity can vary depending on the substituents on the ring.

Explanation: Benzyl halides are more reactive in nucleophilic substitution reactions because the benzyl carbocation formed during the reaction is resonance stabilized by the aromatic ring. The electron-donating nature of the ring stabilizes the positive charge better than in a regular alkyl halide.

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3. Why do allyl halides undergo SN2 reactions faster than alkyl halides?

Answer: Allyl halides undergo SN2 reactions faster because the transition state is stabilized by resonance. The double bond in allyl halides allows the negative charge developed in the transition state to be delocalized across the double bond, leading to a lower activation energy.

Explanation: In an SN2 reaction, the nucleophile attacks the carbon attached to the halogen from the opposite side, leading to a transition state. In allyl halides, the presence of a conjugated π-system stabilizes the transition state through resonance, making the reaction proceed more easily than in alkyl halides, which lack such stabilization.

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4. Explain the mechanism of electrophilic substitution reactions in haloarenes.

Answer: Haloarenes (e.g., chlorobenzene, C₆H₅Cl) undergo electrophilic substitution reactions like nitration, sulfonation, halogenation, etc. The halogen atom, though electron-withdrawing due to its inductive effect (-I), also donates electron density via resonance (+R effect).

Mechanism:

The halogen donates electron density to the ring, activating the ortho and para positions for further substitution. This leads to electrophilic attack primarily at these positions.

However, the overall reactivity of the ring is less than benzene because the halogen is electron-withdrawing inductively, making the ring less reactive than plain benzene.

Explanation: The halogen in haloarenes deactivates the ring but directs substitution to the ortho and para positions due to its +R effect. The deactivating inductive effect (-I) reduces the overall reactivity compared to unsubstituted benzene.

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5. Predict the product of the following reaction: Benzyl chloride (C₆H₅CH₂Cl) reacts with aqueous KOH.

Reaction: C₆H₅CH₂Cl + KOH (aq) → C₆H₅CH₂OH + KCl

Explanation: Benzyl chloride undergoes an SN2 reaction with aqueous KOH, where the hydroxide ion (OH⁻) replaces the chlorine atom. The product formed is benzyl alcohol (C₆H₅CH₂OH). The benzylic carbon is highly reactive due to the resonance stabilization of the intermediate during the reaction, making this substitution process fast and efficient.

These answers provide both a detailed explanation of each concept and an understanding of the reactivity and mechanisms involved.