• The?degree of unsaturation?or?index of hydrogen deficiency?provides information about the number of double or triple bonds in a molecule
• The?IHD?is the number of hydrogen molecules, H₂, needed to convert the molecule to the corresponding saturated, non-cyclic molecule
• There are two ways to solve?IHD?problems. One way is to draw the structure and identify rings and double and triple bonds, counting each one as an?IHD?value of 1.
• The second way is to use a formula,
  • For a compound containing C_xH_y,?IHD= (2x+2-y)/2
  • This is a little complicated, since for the formula to work you need to:
    • ignore O and S
    • count halogens as hydrogen
    • add one C and one H for every nitrogen in the formula

     

   

Index of Hydrogen Deficiency Examples

Answer:

Answer 1:?Ethyne, C₂H_2?IHD= 2?

Answer 2:?Methylbenzene, C₆H₅CH_3,?IHD= 4?

Answer 3:?Propanone,CH₃COCH_3??IHD = 1