Aldehydes Ketones and Carboxylic Acids intext questions solutions: Class 12 Chemistry Chapter 8 intext questions solutions
Textbook | Ncert |
Class | Class 12 |
Subject | Chemistry |
Chapter | Chapter 8 |
Chapter Name | Aldehydes Ketones and Carboxylic Acids Class 12 intext questions solutions |
Category | Intext questions |
Medium | English |
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Question 8.1: Write the structures of the following compounds.
- (i) α-Methoxypropionaldehyde
- (ii) 3-Hydroxybutanal
- (iii) 2-Hydroxycyclopentane carbaldehyde
- (iv) 4-Oxopentanal
- (v) Di-sec-butyl ketone
- (vi) 4-Fluoroacetophenone
Solution 8.1:
(i) α-Methoxypropionaldehyde
(ii) 3-Hydroxybutanal
(iii) 2-Hydroxycyclopentane carbaldehyde
(iv) 4-Oxopentanal
(v) Di-sec-butyl ketone
(vi) 4-Fluoroacetophenone
Question 8.2: Write the structures of products of the following reactions;
(i)
(ii)
(iii)
(iv)
Solution 8.2:
(i)
(ii)
(iii)
(iv)
Question 8.3: Arrange the following compounds in increasing order of their boiling points.
CH3CHO, CH3CH2OH, CH3OCH3, CH3CH2CH3
Solution 8.3: To arrange the compounds in increasing order of their boiling points, let’s consider the types of intermolecular forces that affect boiling points.
- CH₃CHO (acetaldehyde): This molecule contains a polar carbonyl group (C=O), so it experiences dipole-dipole interactions. However, it does not form hydrogen bonds.
- CH₃CH₂OH (ethanol): This molecule has a hydroxyl group (-OH), which allows it to form hydrogen bonds, the strongest type of intermolecular force among these molecules.
- CH₃OCH₃ (dimethyl ether): This molecule is polar, but it does not form hydrogen bonds because there is no hydrogen attached to oxygen. It primarily experiences dipole-dipole interactions and weaker London dispersion forces.
- CH₃CH₂CH₃ (propane): This molecule is nonpolar and only experiences London dispersion forces, the weakest of the intermolecular forces.
Order of Intermolecular Forces (affecting boiling points):
- London dispersion forces (weakest) – propane (CH₃CH₂CH₃)
- Dipole-dipole interactions – acetaldehyde (CH₃CHO) and dimethyl ether (CH₃OCH₃)
- Hydrogen bonding (strongest) – ethanol (CH₃CH₂OH)
Predicted boiling points (increasing order):
- CH₃CH₂CH₃ (propane) – Weak London forces
- CH₃OCH₃ (dimethyl ether) – Dipole-dipole forces
- CH₃CHO (acetaldehyde) – Stronger dipole-dipole forces due to the carbonyl group
- CH₃CH₂OH (ethanol) – Strong hydrogen bonding
Final Order (increasing boiling point):
CH₃CH₂CH₃ < CH₃OCH₃ < CH₃CHO < CH₃CH₂OH
Question 8.4: Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions
- (i) Ethanal, Propanal, Propanone, Butanone.
- (ii) Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone.
Solution 8.4: (i) The +I effect of the alkyl group increases in the order:
Ethanal < Propanal < Propanone < Butanone
The electron density at the carbonyl carbon increases with the increase in the +I effect. As a result, the chances of attack by a nucleophile decrease. Hence, the increasing order of the reactivities of the given carbonyl compounds in nucleophilic addition reactions is:
Butanone < Propanone < Propanal < Ethanal
(ii) The +I effect is more in ketone than in aldehyde. Hence, acetophenone is the least reactive in nucleophilic addition reactions. Among aldehydes, the +I effect is the highest in p-tolualdehyde because of the presence of the electron-donating −CH3 group and the lowest in p-nitrobezaldehyde because of the presence of the electron-withdrawing −NO2 group.
Hence, the increasing order of the reactivities of the given compounds is:
Acetophenone < p-tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde
Question 8.5: Predict the products of the following reactions:
(i)
(ii)
(iii)
(iv)
Solution 8.5:
(i)
(ii)
(iii)
(iv)
Question 8.6: Give the IUPAC names of the following compounds:
(i) Ph CH2CH2COOH
(ii) (CH3)2C=CHCOOH
Solution 8.6:
- (i) 3-Phenylpropanoic acid
- (ii) 3-Methylbut-2-enoic acid
- (iii) 2-Methylcyclopentanecarboxylic acid
- (iv) 2,4,6-Trinitrobenzoic acid
Question 8.7: Show how each of the following compounds can be converted to benzoic acid.
- (i) Ethylbenzene
- (ii) Acetophenone
- (iii) Bromobenzene
- (iv) Phenylethene (Styrene)
Solution 8.7:
(i) Ethylbenzene to benzoic acid
(ii) Acetophenone to benzoic acid
(iii) Bromobenzene to benzoic acid
(iv) Phenylethene (Styrene) to benzoic acid
Question 8.8: Which acid of each pair shown here would you expect to be stronger?
(i) CH3CO2H or CH2FCO2H
(ii) CH2FCO2H or CH2ClCO2H
(iii) CH2FCH2CH2CO2H or CH3CHFCH2CO2H
(iv)
Solution 8.8: (i)
The +I effect of −CH3 group increases the electron density on the O−H bond. Therefore, release of proton becomes difficult. On the other hand, the −I effect of F decreases the electron density on the O−H bond. Therefore, proton can be released easily. Hence, CH2FCO2H is a stronger acid than CH3CO2H.
(ii)
F has stronger −I effect than Cl. Therefore, CH2FCO2H can release proton more easily than CH2ClCO2H. Hence, CH2FCO2H is stronger acid than CH2ClCO2H.
(iii)
Inductive effect decreases with increase in distance. Hence, the +I effect of F in CH3CHFCH2CO2H is more than it is in CH2FCH2CH2CO2H. Hence, CH3CHFCH2CO2H is stronger acid than CH2FCH2CH2CO2H.
(iv)
Due to the −I effect of F, it is easier to release proton in the case of compound (A). However, in the case of compound (B), release of proton is difficult due to the +I effect of −CH3 group. Hence, (A) is a stronger acid than (B).