The Correct Answer and Explanation is:
The correct IUPAC name for the molecule is 5-ethyl-2-methyl-oct-3-yne.
To determine the IUPAC name for the given chemical structure, we follow a systematic set of rules.
First, we identify the principal functional group in the molecule. The structure contains a carbon-carbon triple bond (C≡C), which classifies it as an alkyne. According to IUPAC nomenclature, the name of the molecule will end with the suffix “yne”.
Second, we find the longest continuous carbon chain that includes the triple bond. Let’s expand the condensed structure to visualize the chains more clearly:
CH₃
|c
CH₃ – CH – C≡C – CH – CH₂CH₃
|
CH₂CH₂CH₃
By examining all possible continuous carbon chains that contain the C≡C bond, we find the longest one has eight carbon atoms. This chain begins with one of the methyl groups on the far left, proceeds through the central part of the molecule including the triple bond, and continues down the three-carbon propyl group on the right. Because the longest chain has eight carbons, the parent name is derived from octane, making it an “octyne”.
Third, we number the carbon atoms in this longest chain. The numbering must begin from the end that assigns the lowest possible number (locant) to the first carbon of the triple bond. Numbering from the left side gives the triple bond a starting position at carbon 3. Numbering from the right side would place it at carbon 5. Since 3 is lower than 5, we must number the chain from left to right. This makes the parent name “oct-3-yne”.
Fourth, we identify any substituent groups attached to the main eight-carbon chain. Using the left-to-right numbering, we find a methyl group (–CH₃) attached to carbon 2 and an ethyl group (–CH₂CH₃) attached to carbon 5.
Finally, we assemble the complete name. The substituents are listed in alphabetical order (ethyl comes before methyl), with their positions indicated by numbers. The final IUPAC name is constructed by adding the substituent prefixes to the parent name: 5-ethyl-2-methyl-oct-3-yne.
