Sigma vs. Pi Bonds

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

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YashDeshmukh1D
Posts: 42
Joined: Fri Sep 29, 2017 7:05 am

Sigma vs. Pi Bonds

Postby YashDeshmukh1D » Mon Nov 13, 2017 4:26 pm

Why can atoms in sigma bonds rotate, but those in pi bonds unable to do so? Why does the cylindrical region of electron density only form in sigma bonds but not in pi bonds?

Lindsay H 2B
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Re: Sigma vs. Pi Bonds

Postby Lindsay H 2B » Mon Nov 13, 2017 4:33 pm

pi bonds have 2 areas of overlapping e- density because the p-orbitals overlap side-by-side, so if the atoms in a pi bond were to rotate, then the bond would break. today in lecture, Dr. Lavelle drew the pi bonds like two figure 8s on top of each other, so that both lobes of each pi bond overlapped.

Ramya Natarajan 1D
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Joined: Fri Sep 29, 2017 7:04 am

Re: Sigma vs. Pi Bonds

Postby Ramya Natarajan 1D » Mon Nov 13, 2017 11:16 pm

The way I think of it is that sigma bonds have electrons that can interact completely because they're directly overlapped, so all electrons are equally distributed and consequently can rotate. Pi bonds are more "stiff" because they can only interact peripherally since the electron repulsion coming from the sigma bond gets in the way.

Clara Rehmann 1K
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Joined: Fri Sep 29, 2017 7:03 am

Re: Sigma vs. Pi Bonds

Postby Clara Rehmann 1K » Tue Nov 14, 2017 12:22 pm

Sigma bonds only have one field of electron sharing, so the atoms involved in a sigma bond can rotate independently of one another on that sigma-bond axis and still remain bonded. However, because pi bonds have two areas of electron sharing, no rotation is allowed: If an atom tried to rotate on one of the electron-sharing axises, the other one would be broken.

Alexandria Weinberger
Posts: 51
Joined: Fri Sep 29, 2017 7:03 am

Re: Sigma vs. Pi Bonds

Postby Alexandria Weinberger » Tue Nov 14, 2017 12:46 pm

Sigma bonds can rotate because they are only connected at one point, making the connecting atoms able to move around. Pi bonds cannot rotate because they are connected at two points and the bonds would break if they tried to rotate. If you tried to twist it any way, at least one of the bonds would break.

Aliza Ajmal 1D
Posts: 25
Joined: Fri Sep 29, 2017 7:05 am

Re: Sigma vs. Pi Bonds

Postby Aliza Ajmal 1D » Tue Nov 14, 2017 10:27 pm

if you want a more visual example of pi bonds think about Dr.Lavelle's example in lecture with the 2 chalk pieces between his two pointer fingers. When he moved his finger, one of the chalks fell. The chalks represent the pi bonds' regions of electron density, and rotating would break one of the two regions of electron density that make up a pi bond.


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