Another OCHEM practice question

[babinski bob]

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Here's a question to brush up on your organic chemistry acidity trend knowledge.

Rank the following compounds in order of decreasing acidity


4-methoxybenzoic acid
4-chlorobenzoic acid
Benzoic acid
4-nitrobenzoic acid
3-nitrobenzoic acid
3-methoxybenzoic acid
4-N,N-dimethylaminobenzoic acid

HINT.... the "acid" is at position 1 since it's not explicitly stated.

 

[babinski bob]

i'll bump this up for all the ochem-o-philes...

 

[sdnstud]

most acidic to least acidic:

4-nitrobenzoic acid > 3-nitrobenzoic acid > 4-chlorobenzoic acid > Benzoic acid > 3-methoxybenzoic acid > 4-methoxybenzoic acid


this is probably a trick question, but this is how i would think it through. i used benzoic acid as a reference. nitro and chloro are e withdrawing group so they are more acidic. nitro is a stronger e withdrawing gruop than chloro. nitro is a meta director, thus 4-nitrobenzoic acid is stronger than 3-nitrobenzoic acid.

methoxy is e donating and make the acid less acidic. methoxy is ortho para directing, thus 3-methoxybenzoic acid > 4-methoxybenzoic acid