GED Science TestPhysical ScienceHard
A chemist is attempting to synthesize a compound with a specific three-dimensional structure. They are using a reaction that involves the formation of a triple bond between two carbon atoms. Which of the following statements accurately describes a key characteristic of a triple bond between carbon atoms?
- AIt consists of three sigma (σ) bonds, allowing free rotation.
- BIt consists of one sigma (σ) bond and two pi (π) bonds, restricting rotation.
- CIt consists of two sigma (σ) bonds and one pi (π) bond, allowing free rotation.
- DIt consists of one sigma (σ) bond and one pi (π) bond, allowing free rotation.
Show answer & explanationAnswer & explanation
Correct answer: B. It consists of one sigma (σ) bond and two pi (π) bonds, restricting rotation.
A triple bond between carbon atoms (as in alkynes) is composed of one strong sigma (σ) bond and two weaker pi (π) bonds. The presence of these two pi bonds creates a rigid structure that prevents free rotation around the carbon-carbon axis, unlike single bonds.
Why the other options are wrong
- A. A triple bond does not consist of three sigma bonds; it has only one sigma bond. Sigma bonds generally allow rotation, but the pi bonds in a triple bond prevent it.
- C. This incorrectly describes the number and type of bonds in a triple bond and incorrectly states it allows free rotation.
- D. A double bond has one sigma and one pi bond, but a triple bond has two pi bonds. Pi bonds restrict rotation.
Carbon-Carbon Triple Bond
A covalent bond between two carbon atoms consisting of one sigma (σ) bond and two pi (π) bonds, characteristic of alkynes.
- Strongest and shortest C-C bond type
- One sigma bond, two pi bonds
- Restricts rotation, making the molecule linear around the bond
Memory trick: Sigma is single, Pi is extra, more Pi means no free spin.