IB DP Chemistry: HL復習筆記11.1.1 Index of Hydrogen Deficiency
Index of Hydrogen Deficiency
- 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 CxHy,?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
Worked Example
Deduce the Index of Hydrogen Deficiency in ethyne, C2H2, methyl benzene, C6H5CH3, and propanone, CH3COCH3
Answer:
Answer 1:?Ethyne, C2H2?IHD= 2?
Answer 2:?Methylbenzene, C6H5CH3,?IHD= 4?
Answer 3:?Propanone,CH3COCH3??IHD = 1
Exam Tip
Drawing out the structure is a much faster way to solve IHD problems, but using the formula is helpful when you are struggling to draw the structure
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