[ysk1]

Which--4-nitrophenol or 2-nitrophenol--is more polar?

[Arkcon]

Well, what is the difference between the two?  And what does being a polar molecule mean, for something like CO₂ orH₂O?

[ysk1]

I thought 2-nitrophenol was more polar because it has a stronger net dipole moment, but 4-nitrophenol was actually the one. I still think I'm right though. Why is 4-nitrophenol more polar?

[shelanachium]

Draw the structures.

1: 2-nitrophenol is internally hydrogen-bonded. H of OH group to one of the O's of the NO2 group. This means it will not tend to H-bond to adjacent molecules, and will behave as less polar.

2: In 4-nitrophenol the NO2 and OH groups, which create the polarity, are further apart. The further apart the charges in a polar compound, the greater is its polarity. And any hydrogen-bonds must be between molecules, not within them as in 2-nitrophenol.

[ysk1]

"The further apart the charges in a polar compound, the greater is its polarity."

This is the first time I ever heard that.
I've always been told that polarity only depends on net dipole.


The question was actually on my orgo final. The prof didn't even cover such things and yet he gave such a question. I HATE HIM!!!!!!!!!!!!

[Arkcon]

"The further apart the charges in a polar compound, the greater is its polarity."

This is the first time I ever heard that.
I've always been told that polarity only depends on net dipole.


The question was actually on my orgo final. The prof didn't even cover such things and yet he gave such a question. I HATE HIM!!!!!!!!!!!!

They must have mentioned it in your book, separation of the charges was the concept I was gunning for when I asked you to envision polar molecules.  Check your book for a diagram of water and it's polarity, and see if the answer is there.