WAEC Chemistry 2022 Paper

Concept:IUPAC naming of an alkyl halide requires the longest carbon chain, numbering that gives substituents the lowest locants, and listing substituents alphabetically.Explanation:The condensed structure can be written as $\mathrm{CH_3CH(CH_3)CHClCH(CH_3)CH_2CH_3}$.The longest continuous carbon chain contains six carbon atoms, so the parent alkane is hexane.Number the chain from the end that gives the lowest possible locants to the substituents.Numbering from the left gives the chloro group at carbon 3 and the two methyl groups at carbons 2 and 4.Thus, the chain is numbered from the terminal $\mathrm{CH_3}$ group: position 1, then $\mathrm{CH(CH_3)}$ at 2, $\mathrm{CHCl}$ at 3, $\mathrm{CH(CH_3)}$ at 4, $\mathrm{CH_2}$ at 5, and $\mathrm{CH_3}$ at 6.Substituents are arranged alphabetically: chloro comes before methyl.Therefore, the correct IUPAC name is 3-chloro-2,4-dimethylhexane.Answer:D. 3-chloro-2,4-dimethylhexane.