Explain:
a. Chloral normally exists as chloral hydrate and is used as a hypnotic drug.
b. Ninhydrin, used as a spray reagent for the detection of amino acids, exists as hydrate. Which `(C=O)` is hydrated?

c. Account for the isolation of from the reaction of
with `H_(2)O^(**)` (`O^(**)` represents `O^(18)`, isotope of `O^(16)`.)

Explanation

a. In chloral, strong `bare-` withdrawing `Cl` atoms on `C` atom destabilise the carbonyl group due to repulsion between positive charges. The formation of hydrate overcomes the force of repulsion and hence equilibrium lies to the right.

Moreover, intramolecular `H-`bonding is possible in chloral hydrate [between `(-Cl)` and `(-OH)` groups] which stabilises the molecule.
b. The centre `(C=O)` is hydrated.

The adjacent `delta^(o+)`'s are separated by the hydration of central `(C=O)` group.
If any terminal `(C=O)` is hydrated, there would be repulsion on the adjacent `+delta` charges, e.g.,

c.
Equilibrium between acetone and its hydrate favours the ketone. When hydrate loses water, Path `I` is more feasible because `(C-overset(**)O)` bond is slightly stronger than `(C=O)` bond.