The 12 Molecular Orbitals of Acetylene: σ and π

(The appearance of molecular orbitals may take a few moments)

How to Manipulate JSmol Structures or Click on the JSmol logo.

[For more on acetylene MO's, click here.]

Surfaces

#1 M.O. [1s, σ, occupied]
Surfaces

#2 M.O. [1s, σ, occupied]
Surfaces

#3 M.O. [,σ, C-C, C-H, occupied, 0 nodes]
Surfaces

#4 M.O. [σ C-H, occupied, 1 node]

Surfaces

#5 M.O. [σ C-C, occupied, 2 nodes]
Surfaces

#6 M.O. [π C-C, occupied, XZ-plane]
Surfaces

#7 M.O. [π C-C, occupied, YZ-plane]

Surfaces

#8 M.O. [π C-C, unoccupied, XZ-plane]

Surfaces

#9 M.O. [π C-C, unoccupied, YZ-plane]
Surfaces

#10 M.O. [σ C-C, C-H, unoccupied, 3 nodes]
Surfaces

#11 M.O. [σ C-C, C-H, unoccupied, 4 nodes]
Surfaces

#12 M.O. [σ C-C, C-H, unoccupied, 5 nodes]

Acetylene is a linear molecule containing two carbons and two hydrogens. There are two C-H σ-bonds and one C-C σ-bond. both carbon atoms are sp-hybridized. Each carbon atom has five atomic orbitals (AO) that come into play: 1s, 2s, 2px, 2py and 2pz; each hydrogen has one AO: 1s. Since there are 12 AO's, there are 12 MO's for the molecule. The two MO's at the 1s level are not very important (#1, #2). MO #2 is a low lying anti-bonding orbital. There are six σ-framework MO's ranging from zero to five nodes ( #3, #4, #5, #10, #11, #12). The σ-framework is along the z-axis. There are two bonding π-MO's: 2py and 2px (#6, #7; shown in green). Their corresponding π-anti-bonding orbitals are #8, and #9 (shown in red).