A certain saturated acyclic alkane has a molecular weight of and contains a 2-methyl group. How many — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

The general formula of an alkane is $C_nH_{2n+2}$. Setting the mass: $12n + 2n + 2 = 72 \Rightarrow 14n = 70 \Rightarrow n = 5$. The alkane is a pentane isomer with a 2-methyl group, i.e., 2-methylbutane (isopentane). Its structure is $CH_3-CH(CH_3)-CH_2-CH_3$. It has three $1^\circ$ carbons, giving $3 \times 3 = 9$ primary hydrogens.