Question

The unsaturated factor of H-deficiency index of the molecular formulae ${C_5}{H_{12}}$ is:
(A) 0
(B) 1
(C) 2
(D) 3

Answer 1

Hint : To calculate the hydrogen deficiency index evaluates the total number of multiple bonds and rings present in the structure. HDI is always a positive integer number. The degree of unsaturation or HDI is the capacity of the molecule to connect maximum hydrogen atoms per carbon molecule in the chemical structure

Complete Step By Step Answer:
The compounds with single bonds are called as saturated molecules and the one with $\pi$ bonds having double or triple bonds are known as unsaturated compounds.
The hydrogen Deficiency Index (IHD) is a count of molecules of ${H_2}$ (hydrogen) required to form the complete saturated acyclic structure. The degree of unsaturation or HDI is the capacity of the molecule to connect maximum hydrogen atoms per carbon molecule in the chemical structure.
Presence of every double bond is called as one degree of unsaturation and the presence of every triple bond is called as two degrees of unsaturation.
The formula for calculating HDI is:
Degree of unsaturation $= \dfrac{{2C + 2 + N - H - X}}{2}$
Where
C is Carbon atom = 5
N is nitrogen = 0
H is hydrogen = 12
X is halogen molecule = 0
In above chemical formulae ${C_5}{H_{12}}$
On putting the value we get
Degree of Unsaturation $= \frac{{2 \times 5 + 2 + 0 - 12}}{2}$ $= 0$
Therefore the degree of unsaturation of ${C_5}{H_{12}}$ is $0$ .
Hence the correct option is option (A).

Note :
A molecule which has no double bond or rings is know a saturated molecule and in which the number of hydrogen atom are calculated as
Hydrogen $= (2 \times Carbon) + 2$
Along with this the atom oxygen or any any divalent atom (with valency of 2 electrons does not contribute for the unsaturation number of a compound. The HDI degree gives us the total number of multiple bonds and rings present in the structure but it cannot reveal the independent presence of multiple bonds or rings in the structure.