Organic Chemistry Exam Review – Key Concepts and Problem-Solving Guidance

Q5. How many carbon-carbon sigma bonds are in the following compound?

Background

Topic: Bonding in Organic Molecules

This question tests your understanding of sigma (σ) and pi (π) bonds in organic molecules, especially in compounds with multiple bonds (single, double, triple bonds).

Key Terms and Concepts:

• Sigma (σ) bond: The first bond formed between two atoms; all single bonds are sigma bonds. In multiple bonds, only one is a sigma bond, the rest are pi (π) bonds.

• Pi (π) bond: Additional bonds in double or triple bonds, formed by sideways overlap of p orbitals.

• Triple bond: Consists of one sigma and two pi bonds.

• Single bond: Consists of one sigma bond.

Step-by-Step Guidance

1. Identify all the carbon atoms in the structure. Label them for clarity (e.g., leftmost as C1, middle as C2, rightmost as C3).

2. Examine the bonds between the carbon atoms. Note that a triple bond connects C1 and C2, and a single bond connects C2 and C3.

3. Recall that each carbon-carbon single bond is a sigma bond, and in a triple bond, only one of the three bonds is a sigma bond (the other two are pi bonds).

4. Count the sigma bonds between the carbon atoms: one from the triple bond (C1–C2) and one from the single bond (C2–C3).

Try solving on your own before revealing the answer!

Final Answer: 2 sigma bonds

There is one sigma bond in the triple bond (C1–C2) and one sigma bond in the single bond (C2–C3), for a total of 2 carbon-carbon sigma bonds.

This is because only one sigma bond exists between any two atoms, regardless of whether the bond is single, double, or triple.