Four nitro- or chloro-substituted anilines are shown beside the options (the drawn compound is aniline, pKaH 4.6). Which structure is the weakest base?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: B

o-Nitroaniline (pKaH about -0.3) combines the -I and -M effects of NO2 with the ortho effect (crowding and loss of solvation of NH3+, plus an intramolecular N-H...O bond in the free base). p-Nitroaniline is 1.0, o-chloroaniline 0.6 and m-nitroaniline 2.5.

Practice General Organic Chemistry II: Acids and Bases More on Keto-enol tautomers and ortho effect in drawn compounds

Previous question

More questions on Keto-enol tautomers and ortho effect in drawn compounds

Four carbonyl compounds are shown beside the options (the drawn compound is acetone, for reference). Which structure cannot form an enol? NEET level
Which of the structures shown is the enol tautomer of the ketone drawn? NEET level
The compound shown is an ortho-substituted benzoic acid. It is a stronger acid than benzoic acid mainly because NEET level
The ketone shown can form enols by loss of an alpha hydrogen. Count all distinct enol forms (OH on a carbon that was the carbonyl carbon), c... JEE Main level
The structures shown are four tautomers/isomers of the diketone drawn. Which one is the most stable? JEE Advanced level
The compound drawn is acetone. Four other carbonyl compounds are shown beside the options. Select ALL the structures that have a higher enol... JEE Main level