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Posted: Fri Dec 07, 2018 5:15 pm
What does it mean that sigma bonds allow bound atoms to rotate? What are they rotating between and why don't pi bonds allow rotation of bound atoms?
Posted: Fri Dec 07, 2018 6:32 pm
Sigma bonds do not fixate the atoms in one position because they only bind the two atoms' s orbitals. Pi bonds however, form between the p-orbitals of two atoms and secure the top and bottom of an atom in place. Therefore, the single atom is no longer able to rotate, but must move with the other atom to which it is bound.
Posted: Fri Dec 07, 2018 10:21 pm
Sigma bonds bond end to end, allowing for more rotation (you can try this with your fingers). On the other hand, pi bonds bond side to side, allowing no rotation to occur between molecules, and thus fixing them in place.
Posted: Fri Dec 07, 2018 10:54 pm
This relates directly to labeling molecules as bidentate. My TA gave an example of two aspects of a molecule connected by a double bond versus a single bond. The single bond could spin any way it wanted to, so rotating one aspect of the molecule 180 degrees put the two nitrogen atoms right next to each other and allowed them to bond in another place, making the entire molecule bidentate. However, the other molecule had a double bond and was not able to rotate and become bidentate; she said this is because the pi bond that is always present in double bonds because pi bonds are more horizontal and lock the atoms into place.
Posted: Sun Dec 09, 2018 7:46 pm
Sigma bonds bond end to end, allowing the rotation to occur
Posted: Sun Dec 09, 2018 7:47 pm
However, the pi form between the p-orbitals of two atoms and secure the top and bottom of an atom in place so there can be no rotation occurring