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Useful Concepts | ![]() |
The Index of Hydrogen
Deficiency (IHD), is a count of
how many molecules of H2
need to be added to a structure
in order to obtain the corresponding saturated, acyclic species.
Hence it takes a count of how many rings and multiple bonds are present
in the structure, so IHD can also be thought of as (multiple bonds +
rings)
or (π + r).
When you look at a structure, just count
them up (but take care not
to count any rings twice !)
If you have a molecular formula, CcHhNnOoXx,
then the following equation can be derived:
IHD = 0.5 * [2c+2-h-x+n]
Where does this equation come from ?
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© Dr. Ian Hunt, Department of Chemistry, University of Calgary | ![]() |
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