What is Degree of Unsaturation (DU)?
The Degree of Unsaturation (DU) tells us the number of rings and multiple bonds (double or triple bonds) in an organic molecule. It helps determine the structure of a compound.
Why is DU Important?
When trying to identify an unknown compound, the molecular formula (often determined by mass spectrometry) gives you the types and numbers of atoms. The DU helps you narrow down the structural possibilities.
It tells you how many rings or multiple bonds to consider when drawing potential structures.
This information, combined with other data from techniques like NMR and IR spectroscopy, is essential for determining the complete structure of a molecule.
What DU Tells Us
A molecule’s DU value tells us the total number of rings and/or pi bonds (double or triple bonds) within its structure. It doesn’t tell us where those rings or bonds are, just how many exist in total.
- DU = 0: The molecule is fully saturated. No rings or multiple bonds. Think alkanes.
- DU = 1: One ring or one double bond. Think cycloalkanes or alkenes.
- DU = 2: Two double bonds, one triple bond, two rings, or a combination. Think alkynes or dienes.
- DU = 3 or more: More complex combinations of rings and multiple bonds.
What are other names for Degree of Unsaturation?
DU is also known as:
- Index of Hydrogen Deficiency (IHD)
- Unsaturation Number
- Double Bond Equivalent (DBE)
Can DU be a decimal or negative number?
No, DU is always a whole number (0 or higher). A decimal or negative value means an incorrect calculation or molecular formula.
