Question

What is the index of hydrogen deficiency? What is its formula?

Answer 1

Hint: We have to know that during the determination of the molecular formula of organic molecules we can use the degree of unsaturation. We can say that degree of unsaturation is a technique which obtains the total amount of rings and pi bonds in the organic molecules.

Complete answer:
We have to know that during the determination of the molecular formula of organic molecules, the degree of unsaturation (otherwise called the index of hydrogen insufficiency, or unsaturation index) is a computation that decides the total number of rings and π bonds. An equation is utilized in organic chemistry to help draw structures of organic compounds. It doesn't give any data about those segments exclusively—the particular number of rings, or of double bonds (one pi bond each), or of triple bonds (two pi bonds each). The last structure is confirmed with utilization of NMR, mass spectrometry and IR spectroscopy, just as qualitative investigation.
In simple words, we can say that the index of hydrogen deficiency gives the amount of multiple bonds and rings that are found in the structure of the given compound. We can calculate it by drawing the compound’s structure. We can give the number of multiple bonds, and rings to the index of hydrogen deficiency. When we do not have the structure of the compound, we can use the formula given below to calculate the index of hydrogen deficiency.
The formula that we use is,
$IHD = C - \dfrac{H}{2} - \dfrac{X}{2} + \dfrac{N}{2} + 1$
Here,
IHD is represented as index of hydrogen insufficiency
C is represented as number of atoms of carbons
H is represented as number of atoms of hydrogen
X is represented as number of atoms of halogen
N is represented as number of atoms of nitrogen

Note:
 We have to know that for hydrocarbons, the index of hydrogen deficiency describes the number of rings (or) extra bonds in an unsaturated structure that is similar to the number of pairs of hydrogen that are needed to make the structure of the compound saturated. This is possible by formation of a ring by joining two elements.