Which of the following will have the highest pKb value?
Answer & explanation
Correct answer: option 3
The groups -CH3, -OCH3 and -NH2 are all electron donating groups. When these are substituted at para position in aniline, it stabilizes the respective anilinium ion formed and thus increases the basic strength. Therefore, aniline is the weakest base from the given compounds and will have the highest pKb value