Home › UP Board Class 12 › chemistry › Alcohols Phenols and Ethers › The HYDRATION of propene ($\mathrm{CH_3{-}CH{=}C…
The HYDRATION of propene ($\mathrm{CH_3{-}CH{=}CH_2}$) with $\mathrm{H_2O}/\mathrm{H}^+$ follows Markovnikov's rule. The major product is
A$\mathrm{CH_3CH_2CH_2OH}$ (propan-1-ol)
B$\mathrm{CH_3CH(OH)CH_3}$ (propan-2-ol)
C$\mathrm{CH_3CH_2CH_2{-}H}$ (propane)
D$\mathrm{HOCH_2CH_2CH_2OH}$ (propane-1,3-diol)
Answer & Solution
Correct answer: B. $\mathrm{CH_3CH(OH)CH_3}$ (propan-2-ol)
1. MARKOVNIKOV's rule: in the acid-catalysed addition of $\mathrm{H{-}X}$ (or $\mathrm{H{-}OH}$) across an unsymmetric alkene, the $\mathrm{H}$ goes to the carbon ALREADY bearing MORE H atoms, leaving the $\mathrm{X}$ (or $\mathrm{OH}$) on the more substituted carbon.
2. Mechanism: protonation of the alkene gives the more stable CARBOCATION (here, secondary at C2 vs primary at C1). Water then attacks the cation.
3. Propene: $\mathrm{CH_3{-}CH{=}CH_2}$. C1 (= the $\mathrm{CH_2}$ end) has 2 H's; C2 (the middle) has 1 H. So $\mathrm{H}^+$ adds to C1, leaving the carbocation on C2.
4. Water attacks C2 → propan-2-ol $\mathrm{CH_3CH(OH)CH_3}$.
5. Option A is the ANTI-Markovnikov product (formed by radical addition / peroxide effect — for HBr, not for water). Option C is propane (no OH). Option D is a diol (would need 2 water additions).
_Source: NCERT Class 12 Chemistry Part 2, Ch 7, §7.3 (Preparation — Markovnikov hydration of alkenes), p. 6–7._
Related questions
The KOLBE reaction converts phenol (in the form of sodium phenoxide) into salicylic acid. Ethanol reacts with $\mathrm{PCl_5}$ to give which set of products?Phenol reacts with bromine WATER (aqueous $\mathrm{Br_2}$) at room temperature to giveWhen OXIDISED with strong oxidising agents like acidified $\mathrm{KMnO_4}$, the product oThe REIMER-TIEMANN reaction converts phenol to salicylaldehyde. The reagents areThe WILLIAMSON ETHER SYNTHESIS prepares ethers by reactingThe PHENOXIDE ion is more STABLE than the ethoxide ion becauseEthanol heated with concentrated $\mathrm{H_2SO_4}$ at $443\,\text{K}$ (170°C) gives mainl