Degree of unsaturation

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

 Calculation 
 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.
 Subtract the total from above from the number of hydrogens actually present.
 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

Category:Organic chemistry