Question

Among the following which species has same number of $\sigma$ and $\pi$ bonds.

• A. $C_7{H}_8$
• B. $C_2(CN{)}_4$
• C. $C_2{H}_4$
• D. $C_2{H}_2$

Answer 1

The correct option is B

$C_2(CN{)}_4$

C₂(CN)₄ molecule contains 9$\sigma$ and 9 $\pi$ bonds.

$(CN{)}_2-C=C-(CN{)}_2$
Each C bonded to N would have 2 pi and 1 sigma bond. So that is a total of 8 pi bonds. There is one pi bond between -C=C- in the middle.
The rest of the bonds are all sigma bonds - 1 each between C and N making a total of 4, 1 between the central carbon atoms, and 1 each between the central carbons and the C from CN, making a total of 9 sigma bonds.