Question

How many sigma and pi bonds are present in the following molecules given below:
\[CH \equiv C - CH = CH - C{H_3}\]
A.Sigma $C - C$bonds $ = 4$, sigma $C - H$ bonds $ = 6$, pi $C - C$bonds $ = 3$
B.Sigma $C - C$bonds $ = 5$, sigma $C - H$ bonds $ = 6$, pi $C - C$bonds $ = 2$
C.Sigma $C - C$bonds $ = 4$, sigma $C - H$ bonds $ = 2$, pi $C - C$bonds $ = 5$
D.Sigma $C - C$bonds $ = 4$, sigma $C - H$ bonds $ = 4$, pi $C - C$bonds $ = 4$

Answer 1

Hint: If the compound is having all single bonds then all the bonds are sigma bonds. If the compounds have a double bond then 1 bond is a sigma bond and 1 bond is a pi bond. If the compounds have a triple bond then there are 2 pi bonds and 1 sigma bond.

Complete answer:
Sigma and pi bonds are types of covalent bonds that differ in the overlapping of atomic orbitals. Covalent bonds are formed by the overlapping of atomic orbitals. Sigma bonds are a result of the head-to-head overlapping of atomic orbitals whereas pi bonds are formed by the lateral overlap of two atomic orbitals.
In a molecule, the single bond is a sigma bond. If a molecule has a double bond then one among those bonds is a sigma bond and the other one is the pi bond. And if a molecule has a triple bond, then among them there are two pi bonds and only one sigma bond.
Now we know what are pi bonds and sigma bonds and how to identify them. so let us solve the question.
The molecule given is: \[CH \equiv C - CH = CH - C{H_3}\]
Between the first and the second carbon, there are 2 sigma bonds and 1 pi bond. Between second and third carbon there is only one sigma bond. Between third and fourth carbon there is one pi bond and one sigma bond and between the fourth and the last fifth carbon, there is only one sigma bond. Also, note that the sigma bond is also present in between carbon and hydrogen. Thus the total pi and sigma bonds come out to be:
\[ \pi Bonds = 2 + 1 = 3 \]
\[ \sigma (C - C) = 4 \]
\[ \sigma (C - H) = 6 \]
Therefore the correct option is A. Sigma $C - C$bonds $ = 4$, sigma $C - H$ bonds $ = 6$, pi $C - C$bonds $ = 3$

Note:
Pi Bonds are generally weaker than sigma bonds, owing to the significantly lower degree of overlapping. The pi bond has less electron density between the atoms. A combination of sigma and pi bonds is always stronger than a single sigma bond. A sigma bond is always considered the strongest covalent bond.