Degree of unsaturation

In the analysis of the molecular formula of organic molecules, the degree of unsaturation (DU) (also known as the index of hydrogen deficiency (IHD), double bond equivalents (DBE), or unsaturation index[1]) is a calculation that determines the total number of rings and π bonds.

The final structure is verified with use of NMR, mass spectrometry and IR spectroscopy, as well as qualitative inspection.

The formula for degree of unsaturation is: where ni is the number of atoms with valence vi.

In either case, oxygen and other divalent atoms do not contribute to the degree of unsaturation, as 2 − 2 = 0.

A popular form of the formula is as follows: where C, N, H and X represent the number of carbon, nitrogen, hydrogen and halogen atoms, respectively.