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Chapter 13: Spectroscopy

Infra Red | Nuclear Magnetic Resonance | Ultra-violet/visible | Mass Spectrometry | Getting Structures from Spectra | Index of Hydrogen Deficiency |

Index of Hydrogen Deficiency (IHD)

Chapter 13: Spectroscopy

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 (p + 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?

Determining the IHD for molecules can be useful for the following reasons: What is the IHD of the following molecular formula?
IHD = 2
IHD = 4
IHD = 1
IHD = 1
IHD = 2


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