Question

Which of the following molecules is the weakest base?



(1) CH3CH2CH2CH2NH2

(2) CH3CH2NH2

(3) BrCH2CH2NH2

(4) NO2CH2NH2

Answer 1

Alkyl sustituents have +I effect, which means they push electron density, and bigger the radical the more distinct this effect is. The more electron density on the N atom is, the more its lone-electron pair attractive for protons. Br and NO2 have -I effect, they pull electron density. (they also have +M but there is no conjugated system so it doesn't work). But NO2 is located on $\alpha$-C atom, and Br is on $\beta$-C atom. If a group with electron effect (I or M) is closer to another group, then its influence is bigger than influence of group, located further. From these 4 compounds, in the 4th one NO2 is located closer to NH2 than in other substances, so the answer is 4

4