Williamson's synthesis is an example of nucleophilic substitution reaction. This reaction involves the substitution of one nucleophile with another in a chemical compound. The reaction is named after Alexander Williamson, who first described this method of synthesis in 1850.

Reaction mechanism:
The reaction involves the reaction of an alkoxide ion with an alkyl halide to form an ether. Here is the general mechanism for Williamson's synthesis:

1. Formation of alkoxide ion: The alkoxide ion is formed by deprotonation of an alcohol using a strong base, typically sodium or potassium hydroxide. The alkoxide ion is a strong nucleophile.

2. Nucleophilic attack: The alkoxide ion acts as a nucleophile and attacks the carbon atom of an alkyl halide. The alkyl halide is an electrophile due to the polarity of the carbon-halogen bond.

3. Substitution: The nucleophilic attack results in the displacement of the halogen atom by the alkoxide ion. The product formed is an ether, which contains an oxygen atom bonded to two alkyl groups.

Example:
Let's consider the synthesis of ethyl methyl ether using Williamson's synthesis. The reaction is as follows:

CH3Br + NaOCH2CH3 → CH3OCH2CH3 + NaBr

In this reaction, sodium ethoxide (NaOCH2CH3) is prepared by reacting ethyl alcohol (CH3CH2OH) with sodium hydroxide. The sodium ethoxide then reacts with methyl bromide (CH3Br) to form ethyl methyl ether (CH3OCH2CH3) and sodium bromide (NaBr).

Significance:
Williamson's synthesis is a widely used method for the preparation of ethers. Ethers are important functional groups in organic chemistry and find applications in various fields, including pharmaceuticals, cosmetics, and solvents. This method allows for the synthesis of symmetrical ethers (where both alkyl groups are the same) and mixed ethers (where alkyl groups are different).

Summary:
In summary, Williamson's synthesis is an example of nucleophilic substitution reaction. It involves the reaction of an alkoxide ion with an alkyl halide to form an ether. This method is widely used for the synthesis of ethers and is named after Alexander Williamson, who first described this reaction in 1850.