Question

Four alkyl halides, MeBr, EtBr, iPrBr, and tBuBr, undergo S\(_N\)2 reactions in the presence of hydroxide ion to yield the corresponding alcohols and the halide ion. The CORRECT order of the alkyl halides based on the rates of reactions is

• A. MeBr>EtBr>iPrBr>tBuBr
• B. tBuBr>iPrBr>EtBr>MeBr
• C. iPrBr>tBuBr>EtBr>MeBr
• D. EtBr>iPrBr>tBuBr>MeBr

Hint:

For S\(_N\)2 reactions, less steric hindrance leads to faster reaction rates.

Answer 1

The Correct Option is A

Step 1: Analyze the S\(_N\)2 reaction mechanism.
The S\(_N\)2 mechanism involves the attack of a nucleophile (OH\(^-\)) on the electrophilic carbon of the alkyl halide. The rate of the reaction depends on the steric hindrance of the alkyl group. Less steric hindrance leads to faster reactions.
Step 2: Analyze the alkyl halides.
- MeBr: Methyl group has the least steric hindrance, so it reacts the fastest.
- EtBr: Ethyl group has slightly more steric hindrance than methyl.
- iPrBr: Isopropyl group has even more steric hindrance.
- tBuBr: Tert-butyl group has the highest steric hindrance, making it the slowest.
Step 3: Conclusion.
The order of reactivity is:
- MeBr>EtBr>iPrBr>tBuBr.
Final Answer: \[ \boxed{\text{MeBr>EtBr>iPrBr>tBuBr.}} \]