The intermediate formed during the slowest step involved in the dehydration of alcohol is:
Show Hint
- Protonated alcohol
- Carbanion
- Free radical
- Carbocation
The Correct Option is D
Solution and Explanation
Dehydration of alcohol means removal of water from alcohol to form alkene. In acid-catalysed dehydration of alcohol, the reaction generally proceeds through three steps. First, alcohol gets protonated. Second, water leaves from the protonated alcohol. Third, deprotonation gives alkene. The slowest step is the removal of water, which forms a carbocation.
Step 1: Protonation of alcohol.
Alcohol first reacts with acid. \[ ROH+H^+ \rightarrow ROH_2^+ \] The product is protonated alcohol. This makes water a good leaving group.
Step 2: Loss of water in slow step.
The protonated alcohol loses water. \[ ROH_2^+ \rightarrow R^+ + H_2O \] This step forms carbocation. This is the slowest step because bond breaking occurs here.
Step 3: Formation of alkene.
The carbocation loses a proton to form alkene. \[ R^+ \rightarrow \text{Alkene} \] Therefore, the intermediate formed during the slowest step is carbocation. Hence: \[ \boxed{\text{(D) Carbocation}} \]
Top CBSE CLASS XII Chemistry Questions
- ${AgNO_3}$ does not decompose where :
- Azeotropic mixture of water and HCl boils at 381.5 K. By distilling the mixture it is possible to obtain
Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines.
(i) (CH3 )2CHNH2 (ii) CH3 (CH2 )2NH2 (iii) CH3NHCH(CH3 )2
(iv) (CH3 )3CNH2 (v) C6H5NHCH3 (vi) (CH3CH2 )2NCH3 (vii) m–BrC6H4NH2
Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine
(ii) Secondary and tertiary amines
(iii) Ethylamine and aniline
(iv) Aniline and benzylamine
(v) Aniline and N-methylanilineAccount for the following:
(i) pKb of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not.
(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(iv) Although amino group is o– and p– directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
(v) Aniline does not undergo Friedel-Crafts reaction.
(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.
Top CBSE CLASS XII Elimination reactions Questions
Top CBSE CLASS XII Questions
- 2, b, c are in A.P. and the range of determinant $\begin{vmatrix}1&1&1\\ 2&b&c\\ 4&b^{2}&c^{2}\end{vmatrix}$ is [2, 16]. Then find range of c is
- A boy of mass 50 kg is standing at one end of a, boat of length 9 m and mass 400 kg. He runs to the other, end. The distance through which the centre of mass of the boat boy system moves is
- A capillary tube of radius r is dipped inside a large vessel of water. The mass of water raised above water level is M. If the radius of capillary is doubled, the mass of water inside capillary will be
- A circular disc is rotating about its own axis. An external opposing torque 0.02 Nm is applied on the disc by which it comes rest in 5 seconds. The initial angular momentum of disc is
- A circular disc is rotating about its own axis at uniform angular velocity \(\omega.\) The disc is subjected to uniform angular retardation by which its angular velocity is decreased to \(\frac {\omega}{2}\) during 120 rotations. The number of rotations further made by it before coming to rest is