The hydrocarbon shown, called vinylacetylene, is used in the synthesis of neoprene...

Question

The hydrocarbon shown, called vinylacetylene, is used in the synthesis of neoprene, a synthetic rubber. Identify the orbital overlaps involved in the indicated bond. How many σ bonds are there in vinylacetylene? How many π bonds?

Answer 1

Hi Darmelis.

For Vinylacetylene, looking at the structure, we can see that there is one double-bond and one triple-bond. The rest are single bonds.

Overlaps take place when we have extra orbitals due to bond hybridization. If we look at the C-C double bond, we see that the hybridization of Carbon is SP² since it is bonding to 3 elements. This means that one s orbital and 2 p orbitals combine to give us out SP² but since we have 3 p orbitals, we are left with one p orbital, which is what is giving us this overlap, causing no free rotation of Vinylacetylene.

Similarly, the C-C triple bond is SP since Carbon (C) is only bonded to 2 domains, two other carbons. This means that one S orbital and one P orbital will hybridize to create the SP orbital. Again, we have 3 p orbitals so since only 1 of the 3 orbitals hybridized, the other 2 orbitals will overlap too.

The easiest way to count the sigma (σ) and pi (π) bonds is to follow this guide:

1. For every single bond, that counts as one sigma bond
2. For every bond in a double or triple bond, one of the two or three bonds will count towards a sigma bond, and the rest are pi bonds

Looking at Vinylacetylene, there are 5 single bonds, so all 5 are considered sigma bonds.

For the C-C double bond, one bond is a sigma bond and the other is a pi bond.

For the C-C triple bond, one bond is a sigma bond and the rest are pi bonds, meaning the other 2 are pi bonds.

Adding up the total bonds we just saw, we get:

7 Sigma (σ) Bonds and 3 Pi (π) Bonds.