JEE MainChemistryAlcohols Phenols and Ethers
Consider cyclohexanol as the reference molecule for acid-catalyzed dehydration. Among the following compounds, how many will undergo acid-catalyzed dehydration at a faster rate than cyclohexanol? (i) 1-Methylcyclohexan-1-ol (ii) Cyclohexa-2,4-dien-1-ol (iii) Cyclohex-2-en-1-ol (iv) 1-Phenylethan-1-ol (v) Cyclohexylmethanol (vi) Phenol
Options
- A4
- B3
- C5
- D2
Correct answer
A. 4
Step-by-step solution
The rate of acid-catalyzed dehydration of an alcohol is directly proportional to the stability of the intermediate carbocation formed. Cyclohexanol dehydrates via a secondary carbocation (cyclohexyl cation). Let us evaluate the intermediate carbocations for the given compounds: (i) 1-Methylcyclohexan-1-ol forms a tertiary carbocation, which is more stable than a secondary carbocation. (Faster) (ii) Cyclohexa-2,4-dien-1-ol forms a resonance-stabilized dienyl cation and loses a proton to form the highly stable aromat