Question

$M{g}_2{C}_3$ reacts with water forming propyne. $C_3^{4-}$ has:

• A. Two sigma and two pi bonds
• B. Three sigma and one pi bonds
• C. Two sigma and one pi bonds
• D. Two sigma and three pi bonds

Answer 1

The correct option is A Two sigma and two pi bonds

$M{g}_2{C}_3+4H_{2}O\to 2Mg(OH{)}_2+C_3{H}_4$
When propyne looses its four hydrogen, $C_3^{4-}$ is obtained.
The structure is: ${}^{-}C\equiv C-C^{3-}$
$\therefore$ It has two $\sigma$ bonds and two $\pi$ bonds.