CBSE Class 12 Chemistry Aldehydes Notes

ALDEHYDES, KETONES AND CARBOXYLIC ACIDS

The π Electron cloud of >C=O is unsymmetrical .On the other hand, due to same electonegativity of the two carbon atoms, the π‐ electron of the >C=C< bond is symmetrical.

Nature of carbonyl group:- The Pi electron cloud of >C=O is unsymmetrical therefore, partial positive charge develop over carbon of carbonyl group while negative charge develop over oxygen of carbonyl group and dipole moment is approximate 2.6D.

As we know that anion is more stable than the cation, thus the addition to carbonyl groups should take place via mechanism second which has been further proved in the addition of HCN to carbonyl group.

Reactivity of aldehyde and Ketones is as

HCHO>RCHO>RCOR>RCOOR>RCONH2.

POINTS TO REMEMBER

:-Aldehydes, Ketones and Carboxylic acids are important classes of o rganic compounds containing carbonyl groups.

:-They are highly polar molecules.

:-They boil at higher temperatures than the corresponding hydrocarbons and weakly polar compounds such as ethers.

:-Lower members are soluble in water because they can form Hb ond with water.

:-Higher members are insoluble in water due to large size of their hydrophobic group.

:-Aldehydes are prepared by

a.Dehydrogenation of primary alcohols

b. Controlled oxidation of primary alcohols.

c. Controlled and selective reduction of acyl

:-halides Aromatic aldehydes can be prepared by-. Oxidation of toluene with chromyl chloride or CrO3 in the presence of acetic hydride

b. Formylation of arenes with carbon monoxide and Hydrochloric acid in the p resence of anhydrous aluminiumchloride / Cuprous chloride

c. Hydrolysis of benzal chloride

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