HW Question 4.27

(Polar molecules, Non-polar molecules, etc.)

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Grace Ramey 2K
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Joined: Thu Jul 27, 2017 3:01 am

HW Question 4.27

Postby Grace Ramey 2K » Sun Nov 19, 2017 5:21 pm

Can someone explain why 4.27 part A is polar molecule? It is similar to benzene (which I believe is a nonpolar molecule), except that one CH group is exchanged for a nitrogen. But why would one nitrogen atom cause the whole molecule to become polar?

Thanks for the help!

Aijun Zhang 1D
Posts: 53
Joined: Tue Oct 10, 2017 7:13 am

Re: HW Question 4.27

Postby Aijun Zhang 1D » Sun Nov 19, 2017 5:35 pm

Benzene is nonpolar since it has a symmetrical structure and all the bond dipoles cancel.
But for pyridine, the C-H group is replaced by a nitrogen. And there is a lone pair on nitrogen. The molecule then becomes not symmetrical since C-N bond has different dipole then C-C bond. Also C-H bond dipole polar effect cannot be canceled now.
You can see the 3D structure by this url.
Image

Kelly Kiremidjian 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

Re: HW Question 4.27

Postby Kelly Kiremidjian 1C » Sun Nov 19, 2017 5:37 pm

By replacing the -CH- in Benzene with a Nitrogen atom the dipole moments no longer cancel so it becomes a polar molecule.

Sabah Islam 1G
Posts: 50
Joined: Sat Jul 22, 2017 3:01 am

Re: HW Question 4.27

Postby Sabah Islam 1G » Sun Nov 19, 2017 5:41 pm

The nitrogen atom is more electronegative than than the CH groups present in the rest of the molecule; thus, pulling the electrons shared between the nitrogen and the carbons it is bonded to, towards the nitrogen, having a different electronegativity difference than the difference between the carbons and hydrogens in the molecule. On the other hand, benzene has 6 CH groups bonded to every carbon molecule, which makes the molecule symmetrical and having the same electronegativity differences between carbon and hydrogen present throughout the entire molecule. Also, there is a lone pair present on the nitrogen atom, which further contributes to the polarity of the molecule.

Dana Wilks 3I
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Joined: Fri Sep 28, 2018 12:23 am

Re: HW Question 4.27

Postby Dana Wilks 3I » Wed Nov 28, 2018 11:23 pm

Would we be expected to know the arrangement of C5H5N without being given a diagram?


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