Points to remember in Aldehyde and ketone

Aldol condensation

Carbonyl compounds having acidic $\mathrm{sp}^{3} \alpha-\mathrm{H}$ shows this reaction in presence of dil. $\mathrm{NaOH}$ or dil. acid.

Cannizzaro reaction

Reimer Tiemann Reaction

Perkin reaction

When benzaldehyde (or any other aromatic aldehyde) is heated with the anhydride of an aliphatic acid (containing two $\alpha$-hydrogen atoms) in the presence of its sodium salt, condensation takes place to form a $\beta$-aryl acrylic acid ; e.g., with acetic anhydride and sodium acetate, cinnamic acid is formed.

$ C_6 H_5 CHO + ( CH_3 CO)_2 O \xrightarrow{ CH_3 CO_2 Na} C_6 H_5 CH = CHCO_2 H $

Mechanism

Haloform reaction

Acetaldehyde and methylalkyl ketones react rapidly with halogen $(Cl_2, Br_2$ or $I_2$ ) in the presence of alkali to give haloform and acid salt.

contains acidic hydrogen atom and rest-part of alkyl methyl ketone give acid salt having carbon atom corresponding to alkyl ketone. Preparation of haloform from methylketone involves two steps.

(i) Halogenation

(ii) Alkaline hydrolysis

Other reactions :

- Oxidation of Alcohol

(i)

(ii)

(iii)

(iv)

(v)

Semicarbazide

Semicarbazide is frequently reacted with aldehydes and ketones to produce semicarbazones via a condensation reaction. This is an example of imine formation resulting from the reaction of a primary amine with a carbonyl group.

Acidity of $\alpha$-hydrogens of aldehydes and ketones:

The aldehydes and ketones undergo a number of reactions due to the acidic nature of a-hydrogen. The acidity of $\alpha$-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilization of the conjugate base.

Keto and Enol content

The amount of keto or enol content depends on the stability of the state. carbon with electron withdrawing groups > carbonyl carbons > no. of alpha hydrogens.

Enol content is the number of structures formed after taking one H from its alpha position to carbonyl oxygen. The compound which makes the highest number of enol structure possible, will have the highest enol content.