Question

CH,CH,CH,COOH (acid strength) (iii) Benzoic acid, 4-Nitrobenzoic acid, 3,4-Dinitrobenzoic acid. 4-Methoxybenzoic acid (acid strength) - ) ti)

NEET/Medical Exams

Chemistry

Solution

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(iii) As we have seen in the previous case, electrondonating groups decrease the strengths of acids, while electron-withdrawing groups increase the strengths of acids. As methoxy group is an electrondonating group, 4-methoxybenzoic acid is a weaker acid than benzoic acid. Nitro group is an electronwithdrawing group and will increase the strengths of acids. As 3,4 -dinitrobenzoic acid contains two nitro groups, it is a slightly stronger acid than ( 4- ) nitrobenzoic acid. Hence, the strengths of the given acids increase as: 4-Methoxybenzoic acid < Benzoic acid < 4Nitrobenzoic acid ( <3,4 ) -Dinitrobenzoic acid