Degree of unsaturation (DBE)
The degree of unsaturation (or Double Bond Equivalent, DBE) indicates the number of rings and π bonds in a molecular formula. It's essential for determining the structure of an unknown organic compound from MS or NMR data.
DBE = (2C + 2 + N − H − X) / 2
- O and S do not affect DBE
- N adds 1 to the numerator (trivalent)
- Halogens (X) act like H (subtract 1 each)
DBE reference
- DBE = 0: Fully saturated (e.g., CH₄, C₆H₁₄)
- DBE = 1: One double bond or ring (e.g., C₂H₄, cyclohexane)
- DBE = 2: Alkyne or two double bonds (e.g., C₂H₂, C₄H₆)
- DBE = 4: Benzene (C₆H₆)
- DBE = 7: Naphthalene