Use the formula: DoU = (2C + 2 + N – H – X) / 2
Count C = number of carbons
Count H = number of hydrogens
Count N = number of nitrogens
Count X = number of halogens (F, Cl, Br, I)
Ignore oxygen and sulfur
Substitute the values into the formula
Divide the result by 2
The result is the degree of unsaturation
Each degree of unsaturation = one ring or one double bond
Each triple bond = two degrees of unsaturation