# Question #d0ef2

Feb 23, 2017

By counting the hydrogens as well.

Propyne is a three-carbon alkyne:

$\text{H"_3"C"-"C"-="C"-"H}$

"Prop" means 3, and "yne" means there is a triple bond. Since there are three carbons, the triple bond being across carbons 1 and 2 is the same molecule as being across carbons 2 and 3 by symmetry.

If you draw it out explicitly, you should find:

• Three $\text{C"-"H}$ sigma bonds on the ${\text{CH}}_{3}$
• Two $\text{C"-"C}$ sigma bonds on the main chain
• One $\text{C"-"H}$ sigma bond on the righthand end
• Two $\text{C"-"C}$ pi bonds on the triple bond

In total, this gives six sigma bonds and two pi bonds. Just make sure you know that a triple bond contains one sigma and two pi bonds.