Which will undergo fastest `S_(N)`2 substitution reaction when treated with NaOH ?

Options

A.
B.
C.
D.

Answer

To determine which alkyl halide will undergo the fastest \( S_N2 \) substitution reaction when treated with NaOH, we need to consider the structure of the alkyl halides and the concept of steric hindrance. Here’s a step-by-step solution:

### Step 1: Understand the \( S_N2 \) Mechanism
The \( S_N2 \) (Substitution Nucleophilic Bimolecular) reaction involves a nucleophile attacking the carbon atom that is bonded to the leaving group (the halide). The nucleophile attacks from the opposite side of the leaving group, leading to an inversion of configuration.

**Hint:** Remember that \( S_N2 \) reactions are favored by less steric hindrance around the carbon atom being attacked.

### Step 2: Identify the Degree of Alkyl Halides
Alkyl halides can be classified based on the degree of the carbon atom attached to the halide:
- **1° (Primary)**: The carbon is attached to one other carbon.
- **2° (Secondary)**: The carbon is attached to two other carbons.
- **3° (Tertiary)**: The carbon is attached to three other carbons.

**Hint:** The degree of the alkyl halide affects the steric hindrance experienced by the nucleophile.

### Step 3: Analyze Steric Hindrance
In \( S_N2 \) reactions, steric hindrance plays a crucial role. The more bulky groups attached to the carbon, the slower the reaction will be due to increased steric hindrance.
- **1° alkyl halides** have the least steric hindrance and will react the fastest.
- **2° alkyl halides** have moderate steric hindrance and will react slower than 1°.
- **3° alkyl halides** have the most steric hindrance and will not undergo \( S_N2 \) reactions efficiently.

**Hint:** Consider how many carbon groups are attached to the carbon bearing the halide.

### Step 4: Compare the Given Alkyl Halides
Assuming we have a set of alkyl halides to compare, identify which ones are 1°, 2°, or 3°. The one that is 1° will undergo the fastest \( S_N2 \) reaction.

**Hint:** Look for the structure with the least number of alkyl groups attached to the carbon with the halide.

### Step 5: Conclusion
Based on the analysis, the alkyl halide that is classified as 1° will undergo the fastest \( S_N2 \) substitution reaction when treated with NaOH.

**Final Answer:** The fastest \( S_N2 \) substitution reaction will occur with the 1° alkyl halide.