Degree of unsaturation

Degree of unsaturation (DOU) is a way to figure out how many rings or double bonds are in a molecule.

Calculation

1. Determine the number of hydrogens that should be present if it was completely single bonded. In other words use the formula 2n+2 (with n = the number of carbons present.
2. Subtract the total from above from the number of hydrogens actually present.
3. Take that number and divide it by two. This number is your DOU.

Each degree either equals one ring structure or pi bond. A double bond would have one DOU. A triple bond would have a DOU of two (triple bond is one sigma bond with two pi bonds).

Non-hydrocarbons

For the below, use the same rules as above, using the definitions below.

• Silicon counts as a carbon
• Boron, nitrogen and phosphorus each count as a "half a carbon"
• Halogens (Group 7) count as a hydrogen
• Oxygen, sulfur and selenium (Group 6) can be ignored