Aldehydes, Ketones and Carboxylic Acids - Physical and Chemical Properties

Aldehydes and ketones undergo nucleophilic addition reactions because the carbonyl carbon is electrophilic due to the polar nature of the $>C=O$ bond.

Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric factors and the $+I$ effect of two alkyl groups in ketones which reduces the electrophilicity of the carbonyl carbon.

The boiling points of aldehydes and ketones are higher than non-polar compounds (ethers, hydrocarbons) but lower than alcohols and carboxylic acids because they cannot form intermolecular hydrogen bonds with themselves.

Carboxylic acids have higher boiling points than alcohols of similar molecular mass because they form stable cyclic dimers through extensive intermolecular hydrogen bonding.

Aldehydes reduce Tollens' reagent to form a silver mirror ($[Ag(NH_{3})_{2}]^{+}$) and Fehling's solution to form a red precipitate of $Cu_{2}O$, whereas ketones do not.

Aldehydes and ketones with at least one $\alpha$-hydrogen undergo Aldol condensation in the presence of dilute alkali to form $\beta$-hydroxy aldehydes (aldols) or $\beta$-hydroxy ketones (ketols).

Aldehydes which do not have an $\alpha$-hydrogen atom (e.g., $HCHO$, $C_{6}H_{5}CHO$) undergo Cannizzaro reaction (self-oxidation and reduction) when treated with concentrated alkali.

The acidity of carboxylic acids is enhanced by electron-withdrawing groups (EWG) like $-Cl$, $-NO_{2}$, and $-CN$ through the $-I$ effect, which stabilizes the carboxylate ion ($RCOO^{-}$).

Hell-Volhard-Zelinsky (HVZ) reaction: Carboxylic acids having an $\alpha$-hydrogen are halogenated at the $\alpha$-position on treatment with $Cl_{2}$ or $Br_{2}$ in the presence of small amount of red phosphorus.