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Question Video: Identifying the Part of a Molecule That Indicates Unsaturation Chemistry

Which of the parts of this 5-hexen-3-ol derivative indicates that the molecule is unsaturated? [A] 1 [B] 2 [C] 3 [D] 4 [E] 5

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Video Transcript

Which of the parts of this 5-hexen-3-ol derivative indicates that the molecule is unsaturated? (A) 1, (B) 2, (C) 3, (D) 4, or (E) 5.

To answer this question we need to know what unsaturated means. Unsaturated hydrocarbons are hydrocarbons that have at least one double or triple bond between adjacent carbon atoms. In contrast, saturated hydrocarbons are hydrocarbons that only consist of single covalent bonds between carbon atoms.

In this question, we’ve been given the skeletal structure of a derivative of 5-hexen-3-ol, and we need to determine which of the circled parts indicates that the molecule is unsaturated. Firstly, we need to recognize that in a skeleton formula, the points at which line segments meet and the end of line segments each represent a carbon atom.

With this in mind, let’s take a look at part 1. This section represents a single bond between two carbon atoms. Part 2 is an OH group or a hydroxy group. This group consists of an oxygen atom single bonded to a hydrogen atom. Part 3 is another carbon–carbon single bond. In part 4, there are two lines between the carbon atoms. This represents a carbon–carbon double bond. Lastly, part 5 is a chlorine atom, also called a chloro group.

If we look back at the definitions of unsaturated and saturated hydrocarbons, we see that the main difference between them is that an unsaturated hydrocarbon contains at least one carbon–carbon double or triple bond. Therefore, this molecule is unsaturated because it contains a carbon–carbon double bond.

So the part of the 5-hexen-3-ol derivative that indicates that the molecule is unsaturated is part 4, answer choice (D).

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