In aqueous solution, which is the strongest base among NH3 (conjugate acid pK_a 9.25), C6H5NH2 (4.6), (CH3)3N (9.8) and (CH3)2NH (10.7)?

JEE Main levelSingle correct optionDifficulty 2 of 3g2150

In aqueous solution, which is the strongest base among $NH X_{3}$ (conjugate acid $p K_{a}$ 9.25), $C X_{6} H X_{5} NH X_{2}$ (4.6), $(CH X_{3}) X_{3} N$ (9.8) and $(CH X_{3}) X_{2} NH$ (10.7)?

The base with the highest conjugate-acid

p K_{a}

is the strongest. Dimethylamine (10.7) combines the

+ I

effect of two methyls with good solvation of the

R X_{2} NH X_{2} X^{+}

cation. Aniline is weakest because its lone pair is delocalised into the ring.