Exams › JEE Advanced › Chemistry

Arrange the following alcohols in DECREASING order of their rate of acid-catalysed dehydration with concentrated H2SO4: (1) Cyclohexanemethanol [(cyclohexyl)methanol] — primary alcohol (2) 1-Methylcyclohexan-1-ol — tertiary alcohol (3) 1-Methylcyclohex-2-en-1-ol — tertiary allylic alcohol (4) 4-Methylcyclohexan-1-ol — secondary alcohol

1. 3 > 2 > 4 > 1
2. 2 > 3 > 1 > 4
3. 1 > 2 > 3 > 4
4. 4 > 3 > 2 > 1

Correct answer: 3 > 2 > 4 > 1

Solution

Acid-catalysed dehydration proceeds via E1: protonation of -OH, loss of water to form carbocation, then elimination of H+ to give alkene. The rate-determining step is carbocation formation. Compound 3 (tertiary + allylic) gives the most stable carbocation (resonance with C=C). Compound 2 (tertiary, no resonance) is next. Compound 4 (secondary) is slower. Compound 1 (primary, effectively neopentyl-type) is slowest because primary carbocations are highly unstable.

Related JEE Advanced Chemistry questions

• Which compound listed below cannot be synthesized using the standard Williamson ether synthesis?
• In the reaction between C6H5Br and CH3CH2OH, C6H5Br remains unreactive. However, when C6H5OH reacts with MeCBrMe2, the tert-halide group in CBr undergoes elimination instead of substitution. Therefore, only certain combinations are suitable for ether synthesis.
• When CH3CH2CH2CH2OH is heated with Al2O3 at 350°C, what is the main product formed?
• The compound that does NOT liberate CO₂ on treatment with aqueous sodium bicarbonate solution, is -
• Which type of solution is required to perform the dye test for identifying β-naphthol?
• Among the following alcohols, how many will produce an immediate white turbidity (precipitate) when treated with Lucas reagent (anhydrous ZnCl2 / conc. HCl) at room temperature? The compounds are: (i) 1-butanol, (ii) 2-butanol, (iii) 2-methyl-2-propanol (tert-butanol), (iv) benzyl alcohol.

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →