Which is not true for the major Product of the reaction?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → will react with \(O_3/H_2O-Zn\) dust
Note 1: The given answer is as per the official NTA Answer Key. However, there is more than one correct option for this question, as explained below.
The reactant is 4-methylhex-2-ene. With \( \ce{H3O+} \) it undergoes acid catalysed hydration through a carbocation, and a carbocation rearranges if a more stable one can form. Protonation at C-2 gives a secondary carbocation at C-3; a 1,2-hydride shift from C-4 then gives the more stable tertiary carbocation, which takes up water:
\( \displaystyle \ce{CH3CH=CH-CH(CH3)CH2CH3 + H+ -> CH3CH2-C^+H-CH(CH3)CH2CH3} \)
\( \displaystyle \ce{CH3CH2-C^+H-CH(CH3)CH2CH3 -> CH3CH2CH2-C^+(CH3)CH2CH3} \)
\( \displaystyle \ce{CH3CH2CH2-C^+(CH3)CH2CH3 + H2O -> CH3CH2CH2-C(OH)(CH3)CH2CH3 + H+} \)
So the major product is the tertiary alcohol 3-methylhexan-3-ol, with no C=C bond left.
Option (1) Is an optical isomer — True for the product. The carbinol carbon carries four different groups (OH, CH3, ethyl, propyl), so the product is chiral.
Option (2) Gives white turbidity with Lucas reagent after 5 min — Is also correct. It is not true for the product: a tertiary alcohol gives turbidity with Lucas reagent immediately; turbidity after about five minutes is the behaviour of a secondary alcohol.
Option (3) It dehydrates easily — True for the product. A tertiary alcohol loses water very easily on warming with acid, through a stable tertiary carbocation.
Option (4) will react with O3/H2O-Zn dust — Not true for the product. The C=C bond is used up in the hydration, so the alcohol cannot undergo ozonolysis.
NCERT (2026-27 edition):
By Acid Catalysed Hydration – “Alkenes react with water in the presence of acid as catalyst to form alcohols. In case of unsymmetrical alkenes, the addition reaction takes place in accordance with Markovnikov’s rule.”
Reaction with Hydrogen Halides – “… The difference in reactivity of three classes of alcohols with HCl distinguishes them from one another (Lucas test). Alcohols are soluble in Lucas reagent (conc. HCl and ZnCl2) while their halides are immiscible and produce turbidity in solution. In case of tertiary alcohols, turbidity is produced immediately as they form the halides easily. Primary alcohols do not produce turbidity at room temperature.”
Note 2: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | – | 14-06 S1 30-05 S2 | – |