Why are \(\alpha\)-hydrogen atoms of aldehydes and ketones acidic in nature ?
Show Hint
Solution and Explanation
Step 1: Formation of enolate ion Consider a simple aldehyde or ketone: \[ RCH_2CHO \] Removal of an \(\alpha\)-hydrogen gives: \[ RCH^-CHO \]
Step 2: Resonance stabilization The negative charge formed is delocalized between the \(\alpha\)-carbon and the oxygen atom. \[ RCH^-CHO \leftrightarrow RCH=CHO^- \] Because the negative charge is spread over more than one atom, the conjugate base becomes stable.
Step 3: Effect on acidity Greater stability of the conjugate base increases the tendency of hydrogen ion removal. Therefore \(\alpha\)-hydrogens of aldehydes and ketones show acidic character.
Final Answer \[ \boxed{ \text{\(\alpha\)-Hydrogen atoms are acidic because their removal produces} \\ \text{a resonance-stabilized enolate ion.} } \]
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 Aldehydes And Ketones Questions
- (c) Arrange the following in increasing order of acid strength: phenol, ethanol, water.
- (b) Give a simple chemical test to distinguish between propanal and propanone.
- (c) Arrange the following in increasing order of acid strength: phenol, ethanol, water.
- (b) Give a simple chemical test to distinguish between propanal and propanone.
- Write the stepwise mechanism of nucleophilic addition reactions in the carbonyl compounds.
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