Viewing a single comment thread. View all comments

Any-Broccoli-3911 t1_j5c0zym wrote

C2 exists. It still has only a double bond though, so it has unpaired electrons which makes it very reactive. It will try to link with any other molecules it can.

https://en.m.wikipedia.org/wiki/Diatomic_carbon

Carbon rarely do triple bonds because they are not energically favorable for carbon. It will typically prefer single or double bond.

Carbon cannot do quadruple bonds because only atoms with d electrons can do a quadruple bond, and in practice only the ones in the middle of the d block do.

https://en.m.wikipedia.org/wiki/Quadruple_bond

3

Indemnity4 t1_j5hmdd9 wrote

Quadruple C2 has two pi-bonds, a strong sigma-bond and a second weak sigma-bond.

The electron in the s orbital comes out to play. It's weird.

1

Any-Broccoli-3911 t1_j5howpz wrote

MO theory says it's a double bond while VB theory says it's a quadruple bond. It's still controversial.

https://mappingignorance.org/2013/05/22/c2-molecule-doubly-or-quadruply-bonded/

https://en.m.wikipedia.org/wiki/Quadruple_bond

In MO theory, there are 2 pi bonds from the px and py electrons.

The s electrons and the pz electrons (z is the axis along which the carbons are) can be considered to have a sigma bond and an anti-sigma bond, but having both a bond and an anti-bond is the same as having no bond.

So the total bond order is 2.

In VB theory, they have 3 regular bonds plus a weak one.

Wikipedia also says:

"Quadruple bonds between atoms of main-group elements are unknown. Molecular orbital theory shows that there are two sets of paired electrons in the sigma system (one bonding, one antibonding), and two sets of paired electrons in a degenerate π-bonding set of orbitals. This adds up to give a bond order of 2, meaning that there exists a double bond between the two carbon atoms in a dicarbon (C2) molecule. The molecular orbital diagram of diatomic carbon would show that there are two pi bonds and no sigma bonds. However, a recent paper by S. Shaik et al. has suggested that a quadruple bond exists in diatomic carbon,[7] but this is disputed.[8]"

1