Which of the following sets is in the correct order regarding the property mentioned against them?
Which of the following sets is in the correct order regarding the property mentioned against them?
I, II only
I, III only
II, III only
I, II, III
Solution
I. Key Idea $(-I)$ group, if are present along with $-\mathrm{COOH}$ group in an acid, they increases the acidic property while (+) I groups or groups show hyperconjugation will decreases the acidic property.
(a) $\mathrm{NCCH}_2 \mathrm{COOH}$ : Contain, $\mathrm{NC}$ (i.e. $-I$ ) group along with $-\mathrm{COOH}$, thus will increases the acidic nature.
(b) $\mathrm{FCH}_2-\mathrm{COOH}$ : Contain, F (i.e. $-I$ ) group thus increases the acidic nature. Between $\mathrm{NCCH}_2 \mathrm{COOH}$ and $\mathrm{FCH}_2 \mathrm{COOH}, \mathrm{NCCH}_2 \mathrm{COOH}$ is more acidic due to stronger (-) $I$ effect.
(c) $\mathrm{H}_3 \mathrm{CCH}_2 \mathrm{COOH}$ : Contain, $\mathrm{CH}_3$ group which show hyperconjugation effect and this is least acidic. Hence, the given order is correct.
II) Key Idea (i) Structures which show more resonance structures or hyperconjugation among aldehydes are less reactive.
(ii) Aldehydes are more reactive than ketones.
a) $\mathrm{CH}_3 \cdot \mathrm{CH}_2 \cdot \mathrm{CHO}$ is an aldehyde in which $\mathrm{CH}_3-\mathrm{CH}_2-$ group show hyperconjugation effect.
reactive than $\mathrm{CH}_3 \mathrm{CH}_2-\mathrm{CHO}$ due to resonance effect of Ph-group.
Thus, correct order is $\mathrm{CH}_3 \mathrm{CH}_2 \cdot \mathrm{CHO}>\mathrm{PhCHO}>\mathrm{PhCOCH}_3$ and the given order is not correct.
(III) Key Idea Boiling point of alcohols (due to ability to form $\mathrm{H}$-bond) are higher than that of aldehydes which are more than that of ketones. (due to less steric-hinderance and more surface area in aldehyde group, having same number of C-atoms)
(c) $\mathrm{H}_3 \mathrm{C}-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm{OH}$ is an alcohol thus the given order for boiling point is correct. Hence, option (b) is the correct answer.
