Question

The number of sigma and pi-bonds in but-1-ene-3-yne are:

• A. 5 $\sigma$ and 5 $\pi$
• B. 7 $\sigma$ and 3 $\pi$
• C. 8 $\sigma$ and 2 $\pi$
• D. 6 $\sigma$ and 4 $\pi$

Answer 1

The correct option is B 7 $\sigma$ and 3 $\pi$

Single bond contains only a sigma bond, one double bond contains a sigma and a $\pi$ bond, whereas a triple bond contains a sigma bond and 2 $\pi$ bonds.
So, $C{H}_2=CH-C\equiv CH$
Number of $\sigma$ bonds = 2 + 1 + 1 + 1 + 1 + 1 = 7
Number of $\pi$ bonds = 1 + 2 = 3