Sigma and Pi bonds

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Cristian Carrasco 1F
Posts: 52
Joined: Fri Sep 29, 2017 7:06 am

Sigma and Pi bonds

Postby Cristian Carrasco 1F » Wed Nov 29, 2017 11:32 pm

Can someone tell me whats the importance of sigma and pi bonds and how we determine how many of each do we have?

Vincent Chiang 1L
Posts: 54
Joined: Fri Sep 29, 2017 7:05 am

Re: Sigma and Pi bonds

Postby Vincent Chiang 1L » Thu Nov 30, 2017 12:37 am

Sigma bonds occur when two orbitals, each with 1 electron, overlap end to end to form 1 sigma bond. They allow bound atoms to rotate.
Pi bonds occur when two orbitals, each with 1 electron, overlap side by side to form 1 pi bond. Unlike sigma bonds, pi bonds do not allow bound atoms to rotate.
When considering bonds, if an atom has a single bond, it is one sigma bond; a double bond, it is one sigma bond and one pi bond; and a triple bond, it is one sigma bond and two pi bonds. For example, in C2H4, each C has 3 sigma bonds and 1 pi bond.

Christine Wastila 1H
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Joined: Fri Sep 29, 2017 7:04 am

Re: Sigma and Pi bonds

Postby Christine Wastila 1H » Thu Nov 30, 2017 9:37 pm

To give you a quick answer:
single bond=1 sigma bond
double bond=1 sigma and 1 pi bond
triple bond=1 sigma and 2 pi bonds

Kourtney Nham 1L
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Joined: Fri Sep 29, 2017 7:04 am

Re: Sigma and Pi bonds

Postby Kourtney Nham 1L » Thu Nov 30, 2017 9:49 pm

Can someone explain how these definitions relate to delocalized pi bonds? Do delocalized pi bonds pretty much just refer to resonance?

Hazem Nasef 1I
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Joined: Tue Oct 10, 2017 7:13 am

Re: Sigma and Pi bonds

Postby Hazem Nasef 1I » Thu Nov 30, 2017 10:29 pm

Yes, you are correct. Whenever a compound has resonance, this means that a double or triple bond can be found in multiple locations in the compound. That second or third bond is always a pi bond, and when there is resonance, that means that the electrons involved in the pi bond are delocalized.

Justin Chu 1G
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Re: Sigma and Pi bonds

Postby Justin Chu 1G » Fri Dec 01, 2017 9:07 am

Another instance of delocalization would be in a benzene ring where all the bonds are shared equally over the entire ring.


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