Question

According to Molecular orbital theory which of the following is correct ?

• A. LUMO level for C2 molecule is $\sigma_{2P_{X}}$ orbital
• B. In C2 molecules both the bonds are $\pi$ bonds
• C. In C22– ion there is one $\sigma$ and two $\pi$ bonds
• D. All the above are correct

Answer 1

Answer: (D)

All the above are correct

Answer 2

M.O for C2 = $\sigma$1s2 < $\sigma$1*s2 < $\sigma$2s2 < $\sigma$2*s2

<$\underset{HOMO}{\overset{\pi_{2}p_{y}^{2} = \pi_{2}p_{z}^{2}}{︸}} < \underset{LUMO}{\overset{\sigma_{2}p_{x}}{︸}}$

It is important to note that double bond in C2 consists of both pi bonds because of the presence of four electrons in two pi molecular orbitals C22– $[ \mathrm { C } \equiv \mathrm { C } ] ^ { 2 }$ .