Ok everyone, I hope this will clarify this question. I finally got the response back from my Ochem professor.
Here is my email to him, first, and then you can see his reply. In comparing the ortho, meta, and para positions, the inductive effect is the most important factor. Check it out.
From me to professor--->
[FONT=verdana, helvetica, sans-serif]Dr. Byrd,
[FONT=verdana, helvetica, sans-serif]I'm so grateful for the explanation, and also the descriptive attachment. I don't want to keep on asking questions audaciously, but I can't resist this..
I just want to make sure I'm right. while comparing ortho, meta, and para chloroanilines, we take care of the inductive effect only, by looking at the distance of the Cl from NH2. Therefore, we should say Para is the most, and ortho is the least basic.
Chlorine could have the same effect of OH on the basicity, only if the overlap of Cl's pi orbitals with the ring's pi system was efficient. However, we know that Cl's pi orbitals are bigger than carbon's, so we somehow ignore the positive effect that Cl could exert on the basicity of aniline in the ortho and para positions by favorable ion-dipole interactions. Am I thinking right?
[FONT=verdana, helvetica, sans-serif]Thank you again.
[FONT=verdana, helvetica, sans-serif]Harry.
[FONT=verdana, helvetica, sans-serif]Harry, .
You have summarized the effect of Cl precisely; its effect is strictly inductive, thus dropping off with distance from C bearing N. Electron donation via resonance when Cl is -o or -p to amino is essentially zero for the reasons you stated.
Good luck,
Dr. Byrd
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