Illustrated Glossary of Organic Chemistry

Double bond equivalent (DBE; UN; degree of unsaturation; PBoR [Pi Bonds or Rings]): The number of molecules of H2 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).