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I am doing some exam preparation and I came across this Question which I am finding challenging:

List from least polar to most polar, the following molecules:

Naphthalene, Phenol, 3-aminophenol and chlorobenzene.

I believe I know that Naphthalene is least polar as the benzene ring is very stable however, the confusion arises with chlorobenzene as the substituent Chlorine is very electronegative hence, it is strongly inductively electron-withdrawing thus is less polar than a simple benzene ring. So which is less polar, chlorobenzene or naphthalene?

Also which is most polar? 3-aminophenol or phenol? Phenol has a lone pair on oxygen in the oH group which can donate electrons to the ring, although with 3-aminophenol, both the NH2 and OH donate electrons, so wouldn't 3-aminophenol be more electron rich and hence more polar?

Please give the order of the molecules from least to most polar, explaining the order itself.

Thank you!

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2 Answers 2

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I would expect that the amino phenol is more polar than the phenol. This due to the fact that $\ce{NH2}$ donates electrons to the Benzene ring, making the difference in charge between the Benzene Carbon and the Oxygen stronger.

The Chlorine atom is less electro negative than oxygen (if I'm not mistaken) so that would mean: Naphatlene < Chlorobenzene < Phenol < Amino Phenol.

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I guess that 3- amino phenol is more polar than phenol because both OH and NH2 groups have a (+)-M-effect (donate electrons to the ring) so amino group will support electron donation to the ring.

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  • $\begingroup$ See that's what I thought, I felt that the 3-aminophenol has 2 substituents which donate to the benzene ring and make it more polar as opposed to phenol which only has one substituent donating its electrons to the ring. What is you opinion on the polarity of chlorobenzene and naphthalene? Which one is least polar and why? $\endgroup$
    – user9464
    Commented Dec 3, 2014 at 19:14
  • $\begingroup$ If you draw the C-H dipole moments of Naphthalene, and add them together, what do you see? $\endgroup$
    – Max
    Commented Dec 3, 2014 at 19:30
  • $\begingroup$ I think chlorobenzene is more polar than naphtalene. notice that Cl group has n-electrons around it which increase polarity. $\endgroup$
    – abd.chemist
    Commented Dec 4, 2014 at 15:09

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