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I am facing difficulty in the following problem.

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In my view N,N-dimethylaniline 2 should be the strongest base because it has two methyl groups which increases electron density of N and hence it can donate it easily than in other cases. However I am not sure about it.

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In my opinion, option 4 should be the answer. This is because too much crowding near the nitrogen atom will throw it out of the plane, as a result of the which the lone pair of electrons of nitrogen atom get localized and are better available for accepting the protons. Moreover, presence of $\ce{-CH3}$ groups also increase basicity due to +I effect.

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In my view your answer is correct. Among all the compound, 3rd one is the least basic, due to the presence of $\ce{-N)2}$ group which withdraws the electron density of nitrogen and decrease donating capacity.

While comparing $1$ and $2$, 2nd compound is more basic due to the presence of 2 $\ce{-CH3}$ groups as they are electron withdrawing group makes the lone pair of $\ce{N}$ more available for donation.

Now while comparing $4$ and $2$, 4th compound is the less basic, even though $\ce{-CH3}$ groups is present the -I effect of $\ce{-NO2}$ group reduce the the electron donating effect of methyl .

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  • $\begingroup$ That was what I had thought.but the correct answer is what is posted in the answer above. $\endgroup$ – Pink Dec 27 '16 at 12:08

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