The Correct Answer and Explanation is:
Based on the provided image, here is the correct answer and explanation for question 10.
Correct Answer: 4-ethyl-2,3,5-trimethylheptane
Explanation
The student’s name, 4-ethyl-2,5,5-trimethylhexane, contains several significant errors. The correct IUPAC name for the molecule is 4-ethyl-2,3,5-trimethylheptane. This is determined by following a systematic process and identifying the student’s mistakes.
There are at least three primary errors in the student’s name:
- Incorrect Parent Chain: The most fundamental error is the choice of the parent chain. The student named the molecule as a derivative of hexane, which has a six-carbon backbone. However, the longest continuous chain of carbon atoms in the molecule contains seven carbons. To find this, you must trace all possible paths. The seven-carbon chain makes the correct parent alkane heptane, not hexane. This initial mistake affects all other aspects of the name.
- Incorrect Numbering of the Chain: IUPAC nomenclature requires numbering the parent chain from the end that gives the substituent groups the lowest possible locants, or numbers. The student’s name implies numbering that results in higher locants than necessary. Even if we consider their incorrect hexane chain, numbering from the right side would have produced a lower set of numbers (2,2,3,5) than their implied numbering from the left (2,4,5,5). For the correct heptane chain, numbering must begin from the bottom left to assign the lowest possible locants to the substituents (2, 3, 4, 5).
- Incorrect Identification of Substituents: The student’s name lists substituents that do not accurately represent the groups attached to their chosen hexane chain. For example, they named “5,5-trimethyl,” indicating two methyl groups on carbon 5. The structure, however, shows a single ethyl group at that position. Additionally, the group at carbon 4 on the horizontal chain is an isopropyl group, which the student misidentified as an ethyl group. This shows a misunderstanding of how to correctly identify and name alkyl substituents.
To arrive at the correct name, you first identify the seven-carbon parent chain (heptane). Then, you number it from the end closest to the first branch, which is the bottom left. This places methyl groups at carbons 2, 3, and 5, and an ethyl group at carbon 4. The methyl groups are combined to “2,3,5-trimethyl.” Finally, the substituents are listed alphabetically (ethyl before methyl) to give the final, correct name: 4-ethyl-2,3,5-trimethylheptane.
