Answer:
In organic chemistry, the unsaturation grade formula (also known as the hydrogen deficiency index (HDI) or ring formula plus double bonds1) is used to help draw chemical structures. The formula allows the user to determine how many rings, double bonds and triple bonds are present in the compound to be drawn. It does not give the exact number of rings or double or triple bonds, but gives the sum of rings and double bonds, plus double the number of triple bonds. Verification of the final structure is performed with the use of nuclear magnetic resonance, mass spectrometry and infrared spectroscopy, as well as by inspection. The formula for the degree of unsaturation.
That is, an atom that has a valence of x contributes a total of x-2 to the degree of unsaturation. The result is divided by two, and then increased by
For molecules containing only carbon, hydrogen, monovalent halogens, nitrogen and oxygen, the formula
C + 1 - 0.5 * (H + X - N)
where C = number of carbon atoms, H = number of hydrogen atoms, X = number of halogen atoms, and N = number of nitrogen atoms, 2 gives an equivalent result. Oxygen and other divalent atoms do not contribute to the degree of unsaturation, since (2-2) = 0.
The degree of unsaturation is used to calculate the number of rings and pi bonds, where
Each cycle counts as a degree of unsaturation.
Each double bond counts as a degree of unsaturation.
Each triple bond counts as two degrees of unsaturation.
Each benzene counts as four degrees of unsaturation.
It can also be calculated by the following formula:
G.I. = (2C-H + N-X + 2) / 2, where X is the number of halides.