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Account for the following: (a) Boiling...

Account for the following:
(a) Boiling points of carboxylic acids are higher than those of corresponding alcohols.
(b) The C-O bond in R-COOH is shorter than in R-OH
(c ) Acetic acid in the vapour state has a molecule mass of 120.

Text Solution

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(a)The intermolecular hydrogen bonding and dipole-dipole attraction are greater in carboxylic acids and exists as dimer than in alcohols.
These forces are responsible for higher boiling points of carboxylic acids.
(b) Resonance exists in carboxylic acids. The main contributing resonance structures are:

(III) Resonance structure suggests that there is some double bond character in C-O bond of the acid. This is responsible for the shorter bond length of C-O bond in RCOOH.
(c) Acetic acid undergoes intemolecular hydrogen bonding and exists as a dimer.

Thus, the molecular mass of acetic acid is 120 in vapour state.
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