In the Williamson synthesis of ethers given by the general equation.
`R-X+ R'ONa to R-O-R'` the order of reaction of RX is __________.

Options

A. `CH_3 gt 1^(@) gt 2^(@) gt 3^(@)`
B. `CH_3 lt 1^(@) lt 2^(@) lt 3^(@)`
C. `CH_3 lt 1^(@) lt 2^(@) gt 3^(@)`
D. `CH_3 gt 1^(@) lt 2^(@) lt 3^(@) `

Answer

To determine the order of reaction of alkyl halides (RX) in the Williamson synthesis of ethers, we need to analyze the mechanism involved in this reaction.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The Williamson synthesis involves the reaction of an alkyl halide (RX) with sodium alkoxide (R'ONa) to form an ether (R-O-R'). The general equation is:
\[ R-X + R'ONa \rightarrow R-O-R' + NaX \]

2. **Identifying the Mechanism**:
The reaction proceeds via an SN2 mechanism. In this mechanism, the nucleophile (alkoxide ion, R'O-) attacks the electrophilic carbon atom of the alkyl halide (RX) from the opposite side of the leaving group (X).

3. **Analyzing Steric Hindrance**:
The rate of the SN2 reaction is significantly influenced by steric hindrance. The more sterically hindered the carbon atom attached to the halogen (X), the slower the reaction will be.

4. **Order of Reactivity**:
- **Methyl Halide (CH3X)**: No steric hindrance, fastest reaction.
- **Primary Halide (RCH2X)**: Low steric hindrance, reacts quickly.
- **Secondary Halide (R2CHX)**: Moderate steric hindrance, slower reaction.
- **Tertiary Halide (R3CX)**: High steric hindrance, very slow reaction or may not react via SN2 at all.

5. **Conclusion**:
Based on the analysis, the order of reactivity of alkyl halides in the Williamson synthesis is:
\[ \text{Methyl > Primary > Secondary > Tertiary} \]

### Final Answer:
The order of reaction of RX in the Williamson synthesis of ethers is **Methyl > Primary > Secondary > Tertiary**.

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