Reaction Overview
The dehydration of alcohols to form eugenol involves the elimination of water (H₂O) from an alcohol precursor in the presence of a strong base, such as the ethoxide ion (EtO⁻). Eugenol is a phenolic compound found in clove oil, and its synthesis is a key reaction in organic chemistry.

Mechanism of Dehydration
1. **Protonation of the Alcohol**
- The alcohol (e.g., eugenol precursor) is protonated by the ethoxide ion, enhancing the leaving group ability of the hydroxyl group.
2. **Formation of Carbocation**
- Following protonation, the water molecule leaves, forming a carbocation intermediate. This step is crucial as the stability of the carbocation determines the reaction pathway.
3. **Rearrangement (if necessary)**
- If the carbocation is unstable, it may rearrange to form a more stable carbocation, which can then proceed to the next step.
4. **Nucleophilic Attack**
- The ethoxide ion acts as a base, facilitating the elimination of a proton from a neighboring carbon atom, leading to the formation of a double bond.
5. **Formation of Eugenol**
- The final product is eugenol, characterized by the presence of a phenolic hydroxyl group and a propene side chain.

Conclusion
The dehydration of alcohol to eugenol in the presence of ethoxide ion is a multi-step process involving protonation, carbocation formation, and elimination. This reaction highlights the importance of carbocation stability and the role of strong bases in promoting dehydration reactions. Understanding this mechanism is vital for synthesizing aromatic compounds in organic chemistry, particularly for JEE aspirants.