Question

Which of the following molecules contains only $\pi$ bond?

• A. $B_2$
• B. $C_2$
• C. $C_2{H}_2$
• D. Both (1) & (2)

Answer 1

Answer: (D)

Both (1) & (2)

There can be exclusive pi bonds without existing sigma bonds. Some such molecules are $B_2$ and $C_2$.

$MO$ Theory shows that there are two sets of paired electrons in a degenerate pi bonding set of orbitals.

The paired electrons belong to the pi orbitals ($\pi$ $2px$ and $\pi 2py$ to be precise). It is these paired electrons that are involved in bonding while the rest of the inner shell electrons aren’t.