Q18E - Organic Chemistry (Mcmurry)

Question

would you expect the following carboxylic acid to be more acidic or less acidic than benzoic acid? Explain (Reddish brown=Br)

Step-by-Step Solution

Answer

To check whether the carboxylic acid is more or less acidic than benzoic acid.

Step 1: Representation of model is p-bromobenzoic acid (a)

The compound model can be represented as,

The para positive which is present in p-bromobenzoic acid contains bromine is an electron withdrawing group. It will stabilize the anion of p-bromobenzoyate which produces the p-bromobenzoic acid which lose proton both by inductive and resonance effects. 

Thus, p-bromobenzoic acid is more acidic compared to benzoic acid.

Step 2: Representation of model is p-(N,N-dimethylamino) benzoic acid (b)

The compound model can be represented as,

The presence of N,N-dimethylamino group which present in the para positive in p-(N,N-dimethylamino) benzoic acid results in electron releasing group. It can de-stabilize the production of p-(N,N-dimethylamino) benzoyate anion. 

Thus, It is more acidic than benzoic acid.

Thus p-bromobenzoic acid is more stable then p-( N,N diethyl amino) benzoic acid.