Chemistry - ALCOHOL & ETHER Question with Solution | TestHub

Question Explanation: This question asks us to identify the compound that reacts most rapidly with Lucas reagent.

Concept: Lucas test is based on the formation of a carbocation intermediate. The rate of reaction depends on the stability of the carbocation formed. More stable carbocations react faster.

Solution:  

Option 1: m-Chlorobenzyl alcohol

This compound forms a benzylic carbocation. However, the chlorine substituent at the meta position exerts a –I (negative inductive) effect, which withdraws electron density from the benzylic carbon and destabilizes the carbocation. Since meta-Cl does not provide resonance stabilization, only its –I effect operates.

Option 2: Ethanol

Ethanol is a primary (1°) alcohol. It forms an unstable primary carbocation and therefore reacts very slowly, only on heating.

Option 3: Benzyl alcohol (Ph–CH₂–OH)

Benzyl alcohol forms a benzylic carbocation (Ph–CH₂⁺ ), which is highly stabilized by resonance with the aromatic ring. In the absence of any electron-withdrawing substituents, this carbocation is more stable than that formed in Option 1.

Option 4: Methanol Methanol is also a primary (1°) alcohol and reacts very slowly with Lucas reagent Final Answer: Option (3)