Question

The ratio of sigma and pi bond in mesitylene is:
(A) $ 3 $
(B) $ 7 $
(C) $ 5 $
(D) $ 6 $

Answer 1

Hint :Here, we have to understand the meaning of sigma and pi bonds and then have to draw the structure of mesitylene and then have to count the sigma and pi bonds in the structure then only we can be able to draw the ratio of sigma and pi bonds.

Complete Step By Step Answer:
let us first understand the meaning of sigma and pi bonds as below:
Sigma bond or $ \sigma - $ bond: This is the single bond between two or more atoms with which they are connected by sharing a pair of electrons between them.
Pi-bond or $ \pi - $ bond: There is presence of the double bond between two or more atoms and these bonds satisfy the valence between them out of which one is known as sigma and the other is $ \pi - $ bond.
Now, let us draw the structure of mesitylene compound and it is also known as $ 1,3,5 - {\text{trimethylbenzene}} $ as below:

Now, we have to count all the sigma and pi bonds in this structure to calculate the ratio between them but in above structure we see the compactness so we will draw it with more open structure as below:

Now, let us count all the single bonds and pi- bonds in the above structure we get:
 $ \sigma - bonds = 21 $
 $ \pi - bonds = 3 $
Ratio is obtained between them as:
 $ \sigma :\pi = 7:1 $ or $ \sigma :\pi = 7 $
Thus, the correct answer is option B.

Note :
Just note the additional information about triple bonds that just like double bonds having one sigma and one Pi bonds the triple bonds also have one sigma and two pi- bonds whereas pi bonds are referred to as the cloud of electrons. To understand this read about pi-bonds and understand the concept.