Question

Pent -2-yne has how many $\sigma$ and $\pi$ bonds?

• A. 10 $\sigma$, 2$\pi$
• B. 12 $\sigma$, 2$\pi$
• C. 15 $\sigma$, 2$\pi$
• D. 13 $\sigma$, 3$\pi$

Answer 1

The correct option is B 12 $\sigma$, 2$\pi$

$C{H}_3-C\equiv C-C{H}_2-C{H}_3$

Pent-2-yne has 12$\sigma$ and 2$\pi$ bonds.
No. of $\sigma$ bonds = $C_1$ has 3 C-H bonds + $C_4$ has 2 C-H bonds + $C_5$ has 3 C-H bonds + 4 C-C bonds = 12$\sigma$ bonds.
No. of $\pi$ bonds = 2 bonds between $C_2$ and $C_3$.