Degrees of Unsaturation Calculator
Rings plus π bonds, straight from a molecular formula.
Work out Degrees of Unsaturation. Rings plus π bonds, straight from a molecular formula. Shows the working, not just the answer.
F, Cl, Br, I added together. They count exactly like hydrogen.
Degrees of unsaturation
4
four — often a benzene ring, which is three pi bonds plus one ring
Each degree is one ring or one π bond. A benzene ring is four — three double bonds plus the ring itself — so a DoU of 4 or more on an unknown is the first hint of an aromatic ring. Oxygen and sulfur do not appear in the formula at all, because inserting a divalent atom into a chain does not change the hydrogen count: ethanol C₂H₆O has the same DoU as ethane. Nitrogen adds one to the maximum because it is trivalent; halogens replace a hydrogen one for one, so they subtract.
How the Degrees of Unsaturation Calculator works
Enter the carbon, hydrogen, nitrogen and halogen counts and this gives the degrees of unsaturation — the combined number of rings and π bonds. It is the first thing to work out from an unknown's molecular formula, because a value of four or more immediately suggests an aromatic ring.
Also known as: index of hydrogen deficiency calculator · rings plus double bonds calculator · dou calculator · degree of unsaturation formula
Frequently asked questions
How do I calculate degrees of unsaturation?
DoU = (2C + 2 + N − H − X) ÷ 2, where C is carbon, N nitrogen, H hydrogen and X halogens. Benzene, C₆H₆, gives 4.
Why is oxygen not in the formula?
Because inserting a divalent atom into a chain does not change the hydrogen count. Ethanol, C₂H₆O, holds exactly as many hydrogens as ethane, C₂H₆, so oxygen and sulfur are simply ignored.
What does a DoU of 4 tell me?
Most often a benzene ring — three double bonds plus the ring itself. It could also be four separate features, but on an unknown organic compound a DoU of 4 is the standard prompt to look for aromatic signals in the NMR.
Can degrees of unsaturation be a fraction?
No. A fractional result means the formula is impossible, usually a miscounted hydrogen. Whole numbers only, and never negative.
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