[Winga]

According to reference books and lecture notes, they mentioned that the two pi-orbitals of acetylene overlap and become a cylinder (donut) in shape so that the pi electrons can circulate along the C-C bond axis.

If we figure out the overlapping between these two pi-orbitals, because of the sign of each lobe, there should be a nodal plane in each new orbital after the interaction. Therefore, circulation of e- will be blocked.

So, how to explain the continuity of circulation of e-?

Is it the signs of orbitals can be ignored? But why?

[green-goblin]

Would the signs of the orbitals be opposite?
If they are though I can't see how a pi bond will form, like you said the node would stop any
electron cirulation.

[fishyuyue]

According to reference books and lecture notes, they mentioned that the two pi-orbitals of acetylene overlap and become a cylinder (donut) in shape so that the pi electrons can circulate along the C-C bond axis.(movement of e is not like the moving subject in macroscopic world. In the microscopic world, the electrons obery the Uncertainty Principle)

If we figure out the overlapping between these two pi-orbitals, because of the sign of each lobe, there should be a nodal plane in each new orbital after the interaction. Therefore, circulation of e- will be blocked.

So, how to explain the continuity of circulation of e-?

Is it the signs of orbitals can be ignored? But why?

[Winga]

So, how can the Uncertainty Principle explain it?

[fishyuyue]

using the charge density to describe the movement of the electron is better.

[fishyuyue]

So, how can the Uncertainty Principle explain it?

We can't say Yes or No simply, we'd better consider the possibility of this situation

[Winga]

using the charge density to describe the movement of the electron is better.

But e- density still cannot pass through a nodal plane.

[Winga]

Would the signs of the orbitals be opposite?
If they are though I can't see how a pi bond will form, like you said the node would stop any
electron cirulation.

I mean the overlapping of these two orbitals.

[Winga]

Another one

[movies]

In an alkyne there is practically no barrier to rotation about the two C-C bonds at the termini, so the time-average of these orbitals ends up looking like a cylinder, while at any instant it would look like two orthogonal p-orbitals.

[Winga]

In an alkyne there is practically no barrier to rotation about the two C-C bonds at the termini, so the time-average of these orbitals ends up looking like a cylinder, while at any instant it would look like two orthogonal p-orbitals.

You mean the rotation of the whole molecule along C-C bond axis.
However, this rotation seems that all the atoms are fixed in their own positions, only the pi-orbitals are rotating.
I think the anisotropic effect is due to the circulating of e- in the orbitals, but in this case, it becomes the circulation of orbitals, is it quite strange?

[movies]

You can rotate those orbitals without changing the hybridization of the carbons in the alkyne, so there isn't any barrier.  I don't mean the whole molecule, just think about the pi-orbitals spinning around; nothing else has to change.

[Winga]

You can rotate those orbitals without changing the hybridization of the carbons in the alkyne, so there isn't any barrier.  I don't mean the whole molecule, just think about the pi-orbitals spinning around; nothing else has to change.

Are there any reference books or journals mention about this phenomenon?

[movies]

My textbook from sophomore organic chem. says that the cylindrical shape is due to the fact that the pi-bonds are rather diffuse.  It's doesn't mention any kind of spinning.  I can't think of any good reason why the spinning wouldn't occur though.