Which ketone forms the most hydrate in an aqueous solution?

A ketone in which the carbonyl group is attached to atleast one phenyl group is called an aromatic ketone. The simplest aromatic ketone is acetophenone. The carbonyl group in aromatic ketones is an electron-withdrawing group. Therefore, it is a –I group and makes the ortho-para positions of the benzene ring electron deficient.

An electron-donating group in the ortho-para positions decreases the electron deficiency and thus stabilizes the ketone. While an electron-withdrawing group is present in the ortho-para positions, it further reduces the electron density, thus reducing the stability of the ketone.

The reaction with water forms a hydrate. During the hydrate formation of a carbonyl compound, the C=O bond is replaced by two C-OH bonds forming a germinal diol. The reaction of a compound with water is called hydrolysis, and it is a reversible reaction.

The rate of formation of a hydrate depends on the stability of the compound. If the carbonyl compound is highly stable, the compound remains in its carbonyl form and the hydrate formation rate decreases.

Compound A is benzophenone, and compound B is para nitro-substituted benzophenone.

The Nitro group is an electron-withdrawing group and therefore, decreases the electron density of the ortho-para positions. This reduces the stability of benzophenone. Therefore, benzophenone is more stable than para-substituted benzophenone.

At equilibrium during hydration reaction, the compound can remain in hydrate form or carbonyl form. It depends on the stability of carbonyl.

As the stability of the compound decreases, its reactivity increases; therefore, the fraction of molecules remaining in the carbonyl form decreases.

Therefore, compound B is less stable and therefore, a higher fraction of compound B will be in hydrate form compared to compound A.

Of the given compounds, compound B will form the most hydrate.

The ketone that forms the most hydrate