What is the parent chain of the following compound? hexane heptane octane nonane decane
The Correct Answer and Explanation is:
The correct answer is heptane.
To determine the parent chain of an alkane, we must identify the longest continuous chain of carbon atoms within the molecule. This longest chain provides the base name for the compound according to the IUPAC (International Union of Pure and Applied Chemistry) nomenclature rules. The name is derived from a prefix indicating the number of carbons followed by the suffix “ane” for alkanes.
Let’s analyze the provided skeletal structure. In this type of drawing, each vertex and the end of each line represents a carbon atom. To find the parent chain, we must trace all possible continuous paths from one end of the molecule to another and count the number of carbons in each path.
If we trace the most obvious, somewhat horizontal path across the middle, we might count six carbons, which would incorrectly suggest “hexane.” However, we must be thorough and check all possible routes.
Let’s trace a few potential chains:
- Starting from the propyl group at the top, going down and then left into the isopropyl group: This path consists of 6 carbons.
- Starting from the ethyl group on the lower left, going up and across to the methyl group on the upper right: This path also consists of 6 carbons.
These 6-carbon chains are not the longest possible. Let’s look for a longer one:
3. Start from one of the methyl groups of the isopropyl group on the far left. Trace the path through the center of the molecule and down into the ethyl group on the far right. Counting the carbons along this path: (1) methyl -> (2) CH -> (3) CH -> (4) CH -> (5) CH -> (6) CH2 -> (7) CH3. This is a continuous chain of seven carbon atoms.
Since we have found a chain of seven carbons, which is longer than the 6-carbon chains, we must check if any path is even longer. After examining all other possibilities, such as the path from the bottom-left ethyl group to the bottom-right ethyl group (also 7 carbons), it becomes clear that the maximum number of carbons in any continuous chain is seven.
The prefix for a seven-carbon chain is “hept”. Therefore, the parent chain of this compound is heptane.
