Question

Arrange the following compounds in increasing order of their property as indicated:
(i) ${\text{C}}{{\text{H}}_{\text{3}}}{\text{COC}}{{\text{H}}_{\text{3}}}$,${{\text{C}}_6}{{\text{H}}_5}{\text{COC}}{{\text{H}}_{\text{3}}}$,${\text{C}}{{\text{H}}_{\text{3}}}{\text{CHO}}$ ( reactivity towards nucleophilic addition reaction)
(ii) ${\text{Cl}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$ ,${\text{F}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$,${\text{C}}{{\text{H}}_3} - {\text{COOH}}$ (acidic character)

Answer 1

Increase in steric factor decrease the reactivity of carbonyl towards nucleophilic addition reaction. The factors that stabilize the anion formed by the removal of protons increase the acidity.

Complete answer:
(i) The carbon atom of carbonyl has a slightly positive charge whereas the oxygen atom of carbonyl has a negative charge due to more electronegative of oxygen atom than a carbon atom.
So, a nucleophile attacks on carbonyl carbon, so carbonyl gives nucleophilic addition reaction.
The rate of nucleophilic addition reaction is affected by two factors:
Electronic factor: As the electron-donating group increases the positive charge of the carbon atom of carbonyl decreases which decreases the electrophilicity of carbonyl carbon hence the nucleophilic attack.
Steric factor: As the steric hindrance increases, the approach of nucleophile towards the carbonyl carbon decreases so, the rate of nucleophilic addition reaction decreases.
The reactivity of aldehyde is more than ketone towards nucleophilic addition reaction.
In ketone ${{\text{C}}_6}{{\text{H}}_5}{\text{COC}}{{\text{H}}_{\text{3}}}$ is bulkier so, has more steric hindrance than ${\text{C}}{{\text{H}}_{\text{3}}}{\text{COC}}{{\text{H}}_{\text{3}}}$.
So, the increasing order of reactivity towards nucleophilic addition reaction is as follows:
${{\text{C}}_6}{{\text{H}}_5}{\text{COC}}{{\text{H}}_{\text{3}}}$ < ${\text{C}}{{\text{H}}_{\text{3}}}{\text{COC}}{{\text{H}}_{\text{3}}}$ < ${\text{C}}{{\text{H}}_{\text{3}}}{\text{CHO}}$
(ii) Acidity depends upon the stability of the anion forms by the removal of a proton.
In acids, after the removal of hydrogen, the oxygen gets a negative charge.
In ${\text{F}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$, the electronegativity of fluorine is highest and fluorine shows $- {\text{I}}$ so, it attracts the electron density form the negatively charged oxygen hence stabilise the negatively oxygen atom.
In${\text{Cl}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$, the chlorine shows $- {\text{I}}$ effect so, it attracts the electron density from the negatively charged oxygen hence stabilize the negative oxygen atom.
In${\text{Cl}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$, the methyl group shows $+ {\text{I}}$ effect so, it donates the electron density to the negatively charged oxygen hence destabilize the negative oxygen atom. So, its acidity is minimal.
The $- {\text{I}}$ effect of fluorine is more than the chlorine so, the acidity of ${\text{F}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$ is more than ${\text{Cl}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$.
So, the increasing order of acidic character is as follows:
${\text{C}}{{\text{H}}_3} - {\text{COOH}}$ < ${\text{Cl}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$ < ${\text{F}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{COOH}}$

Note: In aldehyde, the carbonyl group has one hydrogen necessarily and one another group can be alkyl, aryl, etc. whereas in ketone both bonds of carbonyl have alkyl, aryl, etc. so, ketones are more bulky and have more electron donating groups than aldehyde. The groups that donate electron density show $+ {\text{I}}$ effect whereas the groups that attract the electron density show $- {\text{I}}$ effect. Halogens show $- {\text{I}}$ effect.