Question Video: Identifying the Alkene That Cannot Be Formed from the Cracking of Octane | Nagwa Question Video: Identifying the Alkene That Cannot Be Formed from the Cracking of Octane | Nagwa

Question Video: Identifying the Alkene That Cannot Be Formed from the Cracking of Octane Chemistry • Third Year of Secondary School

Octane molecules can be broken down into different types of alkenes during a cracking reaction. Which of the following alkenes cannot be obtained from octane molecules during a cracking reaction? [A] Alkene A [B] Alkene B [C] Alkene C [D] Alkene D [E] Alkene E

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Video Transcript

Octane molecules can be broken down into different types of alkenes during a cracking reaction. Which of the following alkenes cannot be obtained from octane molecules during a cracking reaction?

A cracking reaction is the process where larger organic molecules are broken down into smaller molecules. So, cracking reactions are a type of decomposition reactions. A decomposition reaction is a process where a substance breaks down to form two or more other substances. Cracking reactions are decomposition reactions because larger molecules break down into smaller ones. Cracking can occur in saturated or unsaturated hydrocarbons.

Octane is a saturated hydrocarbon whose prefix oct- indicates that it contains eight carbons. When octane undergoes cracking, a carbon-to-carbon single bond is broken. An alkane and an alkene are produced. The alkane and alkene must each have fewer than eight carbon atoms. Let’s have a look at the number of carbon atoms in our answer choices.

Answer choices (A), (B), (C), and (E) all have fewer than eight carbon atoms. These four alkenes are all possible products in a cracking reaction of octane. Since this question is asking us to identify the alkene that cannot be a possible product, we can eliminate answer choices (A), (B), (C), and (E).

Answer choice (D) is an alkene with eight carbon atoms. In order to be a product from the cracking reaction of an octane molecule, the alkene must have fewer than eight carbon atoms. Therefore, the alkene that cannot be obtained from octane molecules during a cracking reaction is answer choice (D).

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