Question

The IUPAC name of the compound

• A. 5-formylhex-2-en-3-one
• B. 5-methyl-4-oxohex-2-en-5-al
• C. 3-keto-2-methylhex-5-enal
• D. 3-keto-2-methylhex-4-enal

Answer 1

The Correct Option is D

To determine the IUPAC name of the given compound, we need to analyze the structure and apply the appropriate naming conventions according to IUPAC rules.

1. Identify the longest carbon chain that includes the highest priority functional group. Here, the chain should include the aldehyde group, which takes precedence over the ketone group.
2. Number the carbon atoms in the chain such that the highest priority group gets the lowest possible number. The aldehyde group, being a terminal functional group, is always at the first position in nomenclature. As a result, the carbon chain numbering starts from the aldehyde carbon.
3. Identify other substituents and functional groups. In this case, the presence of a keto group and a double bond (alkene) needs to be considered.
4. In the provided options, the compound is described with keto, methyl, and enal (indicating an aldehyde and alkene) functionalities.

Let us evaluate each option:

• 5-formylhex-2-en-3-one: This option incorrectly implies that there is a ketone group at the third position and a formyl group at the fifth position, which violates the priority of functional groups.
• 5-methyl-4-oxohex-2-en-5-al: The numbering is incorrect as the aldehyde (should be at 1) isn't correctly prioritized.
• 3-keto-2-methylhex-5-enal: Here, the numbering of the aldehyde group appears incorrect.
• 3-keto-2-methylhex-4-enal: In this option, the numbering gives priority to the enal group. The "3-keto" correctly positions the ketone group, and the "2-methyl" refers to a methyl group.

The correct structural interpretation that fits this naming is a chain base hex-4-enal with a 3-keto position and a 2-methyl group. The given name and description match the compound, as follows:

• The aldehyde is prioritized, being at position 1, recognized as "enal."
• The "3-keto" correctly identifies the ketone group at position 3.
• "2-methyl" at the second position indicates a methyl group.

Therefore, the correct IUPAC name of the compound is 3-keto-2-methylhex-4-enal.