We know that methoxy group exerts a +M effect, as a result of which basicity should increase even after resonance as +M effect is considered to be stronger than resonance effect.
So by this reason 4-methoxy aniline must be more basic than cyclohexane amine, but this is not true.
I am not able to understand what factor should make cyclohexane amine more basic than 4-methoxy aniline.

  • 1
    $\begingroup$ Cyclohexane amine is aliphatic whereas p-methoxy aniline is aromatic. $\endgroup$ Apr 21 '21 at 3:18
  • $\begingroup$ To get real insights you should compare 4-methoxy aniline with aniline. $\endgroup$
    – aventurin
    May 20 '21 at 19:57

Since you mentioned the $\mathrm +M$ effect, I'm assuming you're familiar with resonance and aromaticity.

This is a structure of cyclohexane amine: enter image description here

Here, the lone pair of electrons present on the Nitrogen atom make it a Lewis Base (an electron donor).

This is a structure of 4-methoxy aniline:

enter image description here

Here the lone pair of Nitrogen is delocalized due to resonance. Hence it's not readily available for donation. That's why 4-methoxy aniline is a weaker base.

  • $\begingroup$ I would like to know the reason as to why this answer was downvoted. Thanks. $\endgroup$
    – m-Xylene
    Apr 21 '21 at 9:48
  • $\begingroup$ Thanks, for the answer, but isn't resonance effect considered to be less dominating than +M effect, in the second there's is a +M effect due to methoxy group, which should make it basic? $\endgroup$
    – green_32
    Apr 21 '21 at 11:23
  • 1
    $\begingroup$ I think you should revise what $\mathrm+M$ and resonance mean, since it does not 'dominate over resonance' :). Due to resonance, the lone pair on Nitrogen isn't local to it, which means that even though there is a methoxy group, 4-methoxy aniline is still a weaker base than cyclohexane amine. $\endgroup$
    – m-Xylene
    Apr 22 '21 at 0:32

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