An alkane with molecular formula undergoes free-radical chlorination () and strictly produces a mixt — Haloalkanes and Haloarenes Chemistry Question
Question
An alkane with molecular formula $C_5H_{12}$ undergoes free-radical chlorination ($Cl_2/h u$) and strictly produces a mixture of only three distinct structural (constitutional) monochlorinated isomers. Which of the following statements apply to the identity and properties of this starting alkane?
💡 Solution & Explanation
Let's test the three pentane isomers ($C_5H_{12}$). 1) 2,2-dimethylpropane (neopentane): Has 12 equivalent $1^\circ$ hydrogens. Yields exactly 1 structural isomer (achiral). Doesn't fit. 2) 2-methylbutane (isopentane): Yields 4 structural isomers. Doesn't fit. 3) n-pentane ($CH_3-CH_2-CH_2-CH_2-CH_3$): Yields 1-chloropentane (achiral), 2-chloropentane (chiral, forms a pair of enantiomers), and 3-chloropentane (achiral). This gives exactly 3 structural isomers. Thus, statement A is true. Statement B is false. Statement C is true (both 1-chloro and 3-chloro are achiral). Statement D is true (2-chloropentane forms an $R/S$ enantiomeric pair).