Illustrated Glossary of Organic Chemistry

Double
bond equivalent
(DBE; UN; degree of unsaturation;
PBoR [Pi
Bonds or Rings]): The number of molecules
of H_{2} that would have to be added
to a molecule
to convert all pi
bonds to single
bonds, and all rings
to acyclic
structures. The DBE number can be calculated from the formula
using the following equation:

DBE = UN = PBoR = C - (H/2) + (N/2)
+1,

where: C = number of carbon atoms, H = number of hydrogen and halogen atoms, and N = number of nitrogen atoms.

One DBE = one ring or one double bond. Two DBE = two rings, two double bonds, or one triple bond, or one ring plus one double bond. A benzene ring requires four DBE (one for the ring plus one for each C=C).