Chapter 12 Aldehydes , Ketones and Carboxylic Acids Notes
12.1 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
12.2 Write the structures of products of the following reactions:
12.3 Arrange the following compounds in increasing order of their boiling points. CH3CHO, CH3CH2OH, CH3OCH3 , CH3CH2CH3
Ans: The increasing order of boiling points of all these compounds of comparable molecular masses is :
The molecular masses of the given compounds are in the range 44 to 46. CH3CH2OH undergoes extensive intermolecular H-bonding, resulting in the association of molecules. Therefore, it has the highest boiling point. CH3CHO is more polar than CH3OCH3 and so CH3CHO has stronger intermolecular dipole − dipole attraction than CH3OCH3⋅
12.4 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.
Hint: Consider steric effect and electronic effect.
Ans: (i) Butanone < Propanone < Propanal < Ethanal
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.
12.5 Predict the products of the following reactions:
12.6 Give the IUPAC names of the following compounds:
Ans: (i) 3-Phenylpropanoic acid
(ii) 3-Methylbut-2-enoic acid
(iii) 2-Methylcyclopentanecarboxylic acid
(iv) 2,4,6-Trinitrobenzoic acid
12.7 Show how each of the following compounds can be converted to benzoic acid.
(i) Ethylbenzene (ii) Acetophenone
(iii) Bromobenzene (iv) Phenylethene (Styrene)
12.8 Which acid of each pair shown here would you expect to be stronger?
(i) CH3CO2H or FCH2CO2H
(ii) FCH2CO2H or ClCH2CO2H
(iii) FCH2CH2CH2CO2H or CH3CH(F)CH2CO2H
Ans: CH3 group with +I effect increases the electron density on the oxygen atom in O – H bond in the carboxyl group and cleavage of bond becomes diffcult. It therefore, decreases the acidic strength.
- H2CFCOOH will be stronger of the two. The presence of electronegative F atom at the α-C causes electron withdrawal from the COOH and facilitates the release of H+.
- CH2FCO2H is a stronger acid for the same reason as stated above. F is more electronegative than Cl, so it withdraws electrons from the carboxyl group to a greater extent.CH3CHFCH2COOH is stronger. Although both the given acids have F atom in them, it is the proximity of F in CH3CHFCH2COOH to the COOH group which makes it more acidic.