WAEC Chemistry 2022 Paper

Concept:The given molecule is an unsaturated hydrocarbon containing a $\mathrm{C=C}$ double bond, so it is named as an alkene using the suffix $\text{-ene}$.Explanation:Expand the condensed structure as $\mathrm{CH_3-CH(CH_3)-CH=CH_2}$. This formula contains a double bond, and the $\mathrm{CH=CH_2}$ part confirms that the double bond is terminal. Select the longest continuous carbon chain that includes this double bond; it has 4 carbons, hence the parent name is $\text{but}$. Number the chain from the end closer to the double bond so that the double-bonded carbons receive the lowest locant, 1. In this numbering, a methyl branch, $\mathrm{-CH_3}$, is present on carbon 3. The parent alkene is but-1-ene, and the methyl group at position 3 is written before the parent name. Therefore, the complete IUPAC name is $\text{3-methylbut-1-ene}$.Answer:The IUPAC name of the compound is $\text{3-methylbut-1-ene}$, so the correct option is C.