How many pi ($\pi$) bonds are there in an alkene with six carbon atoms?

Analysis

The question asks for the number of pi ($\pi$) bonds in an alkene containing six carbon atoms. To solve this, we need to understand the definition of an alkene and the nature of the bonds present in its structure.

Concept Explanation

1. What is an alkene? An alkene is an unsaturated hydrocarbon that contains at least one carbon-carbon double bond ($C=C$). The general formula for a simple alkene with one double bond is $C_nH_{2n}$.
2. Bonding in Alkenes: A double bond consists of two types of bonds: • One sigma ($\sigma$) bond: This is the stronger, primary bond formed by the head-on overlap of orbitals. • One pi ($\pi$) bond: This is the weaker, secondary bond formed by the side-to-side overlap of p-orbitals.
3. The Rule: In any molecule, the number of pi bonds is determined by the number of double or triple bonds present. A single double bond contains exactly one pi bond.

Step-by-Step Solution

• Step 1: Identify the structure of the alkene. An alkene with six carbon atoms (hexene) has the molecular formula $C_6H_{12}$.
• Step 2: Determine the number of double bonds. Unless specified as a "diene" or "triene," a standard alkene is defined by the presence of a single double bond.
• Step 3: Calculate the pi bonds. Since a single double bond contains exactly one pi bond, an alkene with one double bond will have exactly one pi bond, regardless of the number of carbon atoms in the chain.

Conclusion

Whether the chain has two carbons (ethene) or six carbons (hexene), as long as it is a simple alkene, there is only one double bond in the structure. Therefore, there is only one pi bond.

Exam Tip: Always remember that in organic chemistry, a single bond is one $\sigma$ bond, a double bond is one $\sigma$ and one $\pi$ bond, and a triple bond is one $\sigma$ and two $\pi$ bonds. Don't let the number of carbon atoms distract you—focus on the functional group (the double bond)!