Chemistry - Nomenclature Question with Solution | TestHub

The longest chain has 6 carbons: $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{CH}(\mathrm{C}{\mathrm{H}}_3)\mathrm{CH}({\mathrm{C}}_2{\mathrm{H}}_5)\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$ (hexane), with a methyl and an ethyl group on adjacent carbons.

The locants are {3,4} from either end, so the tie is broken alphabetically: ethyl gets ${\mathrm{C}}_3$ and methyl gets ${\mathrm{C}}_4$.

Name: 3-ethyl-4-methylhexane. (A) and (C) break the alphabetical rule or the numbering rule, and (D) picks a shorter chain.