Question

One mole trilinolein $\left( X \right)$ on hydrogen, given $Y$, where $9$ moles of hydrogen are found to be consumed. Then, number of pi bonds in $X$ are:
A) $3$ per molecule
B) $3$ per chain of fatty acid
C) $6$ per molecule
D) $9$ per chain of fatty acid

Answer 1

Hint: $9$ moles of hydrogen correspond to $9$ moles of double bonds. Also, pi Bonds can only form in double and triple bonds, like a typical triple bond, let say acetylene $\left( {HC \equiv CH} \right)$ consists of one sigma bond and two pi bonds.

Complete answer:
We know that $9$ moles of hydrogen corresponds to $9$ moles of double bonds.
So, Trilinolein $\left( X \right)$ contains $3$ chains of fatty acids.
So, the number of pi bonds in $X$ are $3$ per chain of fatty acid.
A fatty acid is defined as the carboxylic acid with a long aliphatic chain that is maybe saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain, having an even number of carbon atoms, mostly from $4$ to $28$. We usually cannot find fatty acids in organisms that exist alone, but instead, fatty acids exist as three main classes of esters. Those are triglycerides, phospholipids, and cholesteryl esters.
Trilinolein (also called Glyceryl trilinoleate with formula ${C_{57}}{H_{98}}{O_6}$) is a compound of triglyceride, in which glycerol is esterified with linoleic acid (a chemical compound of formula ${C_{18}}{H_{32}}{O_2}$)
Now, a pi bond is formed, when the lobe of one atomic orbital overlaps side-to-side another atomic orbital and thereby, resulting in a covalent bond, along a plane perpendicular to a line connecting the nuclei of the atoms (denoted by $\pi $).
Hence option B is correct .


Note:
We should remember one thing that pi Bonds can only form in double and triple bonds. But, do not form in single bonds (in most cases). For example, a typical triple bond, let's say acetylene $\left( {HC \equiv CH} \right)$ consists of one sigma bond and two pi bonds, where two mutually perpendicular planes contain the bond axis.