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4.Chemical Bonding and Molecular Structure
hard
According to $MOT$ which of following is correct
A
$LUMO$ level for $C_2$ molecule is $\sigma 2p_x$ orbital
B
In $C_2$ molecule both bounds are $\pi $ bonds
C
In $C_2^{-2}$ ion there is one $\sigma $ and two $\pi $ bonds
D
All above are correct
Solution
$(A) \,M.O.$ for $C_2=\sigma_1 s^2\,<\,\sigma_1^* s^2\,<\,\sigma_2 s^2\,<\,\sigma_2^* s^2\,<\,\underbrace{\pi_2 p_y^2=\pi_2 p_z^2}_{H O M O}\,<\,\underbrace{\sigma_2 p_x}_{L U M O}$
Hence, $LUMO$ is $\sigma_{2 p_x}$.
$(B)$ It is important to note that double bond in $C_2$ consists of both $pi$ bonds because of the presence of four electrons in two pi molecular orbitals.
$(C)\,C_2^{2-}$ has two $pi$ bonds and one sigma bond.
Standard 11
Chemistry
