CH; CH2CHCH3 CH3 CH;CH2- H CH2CH(CH3)2
The Correct Answer and Explanation is:
The correct IUPAC name for the molecule represented by the Newman projection is 4-isobutyl-3,5-dimethylheptane.
Explanation:
Interpreting the Newman Projection:
A Newman projection shows the arrangement of substituents around a specific carbon-carbon bond. We identify the groups attached to the front carbon (represented by the vertex where bonds meet) and the back carbon (represented by the circle). Based on the labels in the diagram, the six substituents are:
Front Carbon: Ethyl (-CH₂CH₃), Methyl (-CH₃), and Hydrogen (-H).
Back Carbon: sec-Butyl (-CH(CH₃)CH₂CH₃), Isobutyl (-CH₂CH(CH₃)₂), and Hydrogen (-H).
Determining the Longest Carbon Chain (Parent Chain):
With the structure identified as (CH₃)(CH₃CH₂)CH-CH(CH(CH₃)CH₂CH₃)(CH₂CH(CH₃)₂), we must find the longest continuous chain of carbon atoms.
There are two possible paths that result in the longest chain, both of which are seven carbons long (a heptane):
Path A: The chain runs from the ethyl group, through the central C-C bond, and through the sec-butyl group.
Chain: CH₃-CH₂-C(front)-C(back)-CH(CH₃)-CH₂-CH₃
Substituents: a methyl group on the front carbon, an isobutyl group on the back carbon, and a methyl group as part of the sec-butyl branch.
Numbering this chain gives substituents at positions 3, 4, and 5. This leads to the name 4-isobutyl-3,5-dimethylheptane.
Path B: The chain runs from the ethyl group, through the central C-C bond, and through the isobutyl group.
Chain: CH₃-CH₂-C(front)-C(back)-CH₂-CH(CH₃)-CH₃
Substituents: a methyl group on the front carbon, a sec-butyl group on the back carbon, and a methyl group as part of the isobutyl branch.
Numbering this chain gives substituents at positions 3, 4, and 6. This leads to the name 4-sec-butyl-3,6-dimethylheptane.
Applying IUPAC Naming Rules:
According to IUPAC rules, when two different chains have the same maximum length, we choose the one that results in the lower set of locants (positions) for the substituents.
Comparing the locant sets: {3, 4, 5} for Path A versus {3, 4, 6} for Path B.
At the first point of difference, 5 is lower than 6. Therefore, Path A is the correct parent chain.
Assembling the Final Name:
The parent chain is heptane. The substituents are two methyl groups at positions 3 and 5, and one isobutyl group at position 4. When writing the name, substituents are listed alphabetically (‘isobutyl’ comes before ‘methyl’).
Therefore, the final, correct IUPAC name is 4-isobutyl-3,5-dimethylheptane.
