Which compounds can be prepared in high yield by halogenation of an alkane? (a) 2-Chloropentane (b) Chlorocyclopentane (c) 2-Bromo-2-methylheptane (d) \((R)\)-2-Bromo-3-methylbutane (e) 2-Bromo-2, 4,4-trimethylpentane (f) Iodoethane

In halogenation, an alkane reacts with a halogen to form a haloalkane. This reaction occurs via free radical mechanism, which can generate different product mixtures depending on the substrate's structure and employed halogen. The order of reactivity for halogens in halogenation is F2 > Cl2 > Br2 > I2. However, fluorination (reaction with F2) is too explosive and iodination (reaction with I2) is too slow to produce any products in high yields. So, we will focus on chlorination and bromination.

We will now assess each compound to determine if it can be prepared in high yield by halogenation of an alkane: (a) 2-Chloropentane: We can obtain this compound by chlorination of pentane, which might occur at any carbon. However, due to the similar reactivity of the carbons present in pentane, the selectivity for the formation of 2-chloropentane is poor, leading to a low yield. This compound cannot be prepared in high yield. (b) Chlorocyclopentane: This compound can be obtained by chlorination of cyclopentane. Since all hydrogens present in cyclopentane are equivalent, chlorination occurs with high selectivity and yield. This compound can be prepared in high yield. (c) 2-Bromo-2-methylheptane: We can obtain this compound by bromination of 2-methylheptane. Due to the higher reactivity of secondary carbons compared to primary carbons in bromination, the major product will be 2-bromo-2-methylheptane, forming in a high yield. This compound can be prepared in high yield. (d) \((R)\)-2-Bromo-3-methylbutane: To selectively obtain this compound in high yield by bromination of 3-methylbutane, the reaction should proceed with stereoselectivity and regioselectivity. However, bromination is a regioselective process but not stereoselective, so both \((R)\) and \((S)\) isomers will form. This compound cannot be prepared in high yield as a single stereoisomer. (e) 2-Bromo-2, 4,4-trimethylpentane: This compound can be obtained by bromination of 2,4,4-trimethylpentane. Bromination will preferentially occur at the tertiary carbon due to its higher reactivity, leading to the desired compound with good yield. This compound can be prepared in high yield. (f) Iodoethane: Iodination is too slow to produce significant amounts of products, making it impossible to prepare iodoethane from ethane through iodination in high yield. This compound cannot be prepared in high yield.

Based on the analysis, the compounds that can be prepared in high yield by halogenation of an alkane are: - Chlorocyclopentane (b) - 2-Bromo-2-methylheptane (c) - 2-Bromo-2, 4,4-trimethylpentane (e)