NEET 2021 Chemistry Question 73 Solution

Break down the IUPAC components: - Root word: dec $\implies$ longest continuous carbon chain containing the double bond has 10 carbon atoms. - Suffix: -4-ene $\implies$ double bond is between carbon-4 and carbon-5. - Substituents: 2,6-dimethyl $\implies$ methyl groups ($-CH_3$) are located at carbon-2 and carbon-6.

Trace the carbon skeleton of Structure (1) starting from the right-hand isopropyl terminus: - $C_1$: terminal methyl group - $C_2$: carbon with vertical methyl branch - $C_3$: $-CH_2-$ methylene carbon - $C_4=C_5$: internal double bond (dec-4-ene) - $C_6$: carbon with methyl branch - $C_7-C_8-C_9-C_{10}$: linear butyl tail ($-CH_2-CH_2-CH_2-CH_3$) Total carbon chain length $= 10$. The double bond is at position 4, and substituents are at 2 and 6. Thus, Structure (1) is identically 2,6-dimethyldec-4-ene.

- Structure (2): Double bond is located towards the bottom at position 5 or 6. - Structure (3): The double bond connects directly to the carbon adjacent to C2, placing the double bond at position 3 (dec-3-ene). - Structure (4): The double bond is located between the branch carbon and the next carbon, giving an incorrect substituent position.