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Aldehydes, Ketones and Carboxylic Acids

Short Answer Type

321.

Explain the mechanism of aldol condensation using ethanal as an example.

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322.

Account for the following:
Carboxylic acids with five or less carbons are water soluble, but many with six or more carbons dissolves in alcohols.

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323.

Account for the following:
Carboxylic acids exist as dimers in the vapour phase.

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324. Illustrate the mechanism of reaction of carbonyl group with an ammonia derivative, H₂N—Z.

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325. Account for the fact that the C—O bond in RCOOH is shorter than in ROH ?

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326. Compare the reactivities of the C = O in RCOOH and RCHO towards nucleophiles.

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Long Answer Type

327. Why is benzoic acid a stronger acid than phenol?

Benzoic acid is a stronger acid than phenol because the benzoate ion is stabilised by two equivalent resonance structures in which the negative charge is present at the more electronegative oxygen atom.

The conjugate base of phenol, a phenoxide ion, has non-equivalent resonance structures in which the negative charge is at the less electronegative carbon atom. Thus, the benzoate ion is more stable than phenoxide ion. Hence, benzoic acid is a stronger acid than phenol.