4. Melting points of aliphatic monocarboxylic acids shows alternation or oscillation effect, i. e., the m. p. of an acid with even number of carbon atoms is higher than the next lower and next higher homologue containing odd number of carbon atoms. This is because, in case of acids with even number of carbon atoms, the terminal-CH3 and-COOH groups lie on the opposite sides of the zig-zag chain. As a result, they get closely packed in the crystal lattice.
5. Glacial acetic acid is completely pure acetic acid and represents the solid state of acetic acid. Below 16.6 ° C temperature pure acetic acid is converted into ice like solid hence it is called glacial acetic acid.
Chemical Properties of Carboxylic Acids
Carboxylic acids do not give reactions of carbonyl groups as it enters into resonance with lone pair of O of-OH group.
( i) Acidity
Above reactions are used to detect the presence of carboxyl group Ul an organic compound,
Carboxylic acids dissociate in water to give resonance stabilised carboxylate anions and hydronium ion.