Counting Pi Bonds in HC≡CCH=CHCH3

The question asks us to determine the number of \(\pi\) bonds present in the molecule with the structural formula \(\text{HC} \equiv \text{CCH} = \text{CHCH}_3\). To do this, we need to look at the types of bonds between the carbon atoms.

In organic molecules, different types of bonds exist between atoms:

• A single bond (\(\text{-}\)) consists of one \(\sigma\) bond.
• A double bond (\(\text{=}\)) consists of one \(\sigma\) bond and one \(\pi\) bond.
• A triple bond (\(\text{≡}\)) consists of one \(\sigma\) bond and two \(\pi\) bonds.

Let's examine the bonds in the given molecule \(\text{HC} \equiv \text{CCH} = \text{CHCH}_3\) from left to right:

• Between the first carbon and hydrogen (\(\text{H}-\text{C}\)): This is a single bond, containing 1 \(\sigma\) bond.
• Between the first and second carbon atoms (\(\text{C} \equiv \text{C}\)): This is a triple bond. A triple bond contains 1 \(\sigma\) bond and 2 \(\pi\) bonds.
• Between the second and third carbon atoms (\(\text{C}-\text{CH}\)): This is a single bond, containing 1 \(\sigma\) bond.
• Between the third and fourth carbon atoms (\(\text{CH} = \text{CH}\)): This is a double bond. A double bond contains 1 \(\sigma\) bond and 1 \(\pi\) bond.
• Between the fourth and fifth carbon atoms (\(\text{CH}-\text{CH}_3\)): This is a single bond, containing 1 \(\sigma\) bond.
• The carbon-hydrogen bonds in the \(\text{CH}\) and \(\text{CH}_3\) groups are all single bonds, containing only \(\sigma\) bonds.

To find the total number of \(\pi\) bonds, we add up the \(\pi\) bonds from the multiple bonds:

• From the triple bond (\(\text{C} \equiv \text{C}\)): 2 \(\pi\) bonds
• From the double bond (\(\text{CH} = \text{CH}\)): 1 \(\pi\) bond

Total number of \(\pi\) bonds = 2 (from triple bond) + 1 (from double bond) = 3 \(\pi\) bonds.

Therefore, there are 3 \(\pi\) bonds in the molecule \(\text{HC} \equiv \text{CCH} = \text{CHCH}_3\).