Question Video: Identifying the Displayed Formula for but-2-Ene Molecules Chemistry • 7th Grade

Video Transcript

Which of the following molecules is but-2-ene?

The prefix but- means that the molecule contains a chain of four carbon atoms. As such, we can eliminate answer choice (B) as this molecule only contains a three-carbon-atom chain. We can also eliminate answer choice (C) as this molecule contains a five-carbon-atom chain. The suffix -ene indicates that the molecule is an alkene, an unsaturated hydrocarbon that contains at least one carbon–carbon double bond. This means that we can eliminate answer choice (D), as this molecule contains a triple bond, called an alkyne, instead of a double bond.

The number two is the position number of the alkene in the carbon atom chain. This means that the double bond begins with the second carbon atom of the chain and connects carbon atoms two and three. The remaining answer choice with a double bond between the second and third carbon atoms of the chain is answer choice (E). The displayed formula that correctly represents but-2-ene is answer choice (E).