객관식
Which of the following statements best describes the mechanism of an reaction?
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7. Substitution Reactions
SN2 Reaction
객관식
Arrange the following compounds in order from fastest to slowest reaction rate when reacting with as the nucleophile: 1-bromopropane, 2-bromopropane, 2-bromo-2-methylpropane.
A
2-bromo-2-methylpropane > 1-bromopropane > 2-bromopropane
B
2-bromopropane > 1-bromopropane > 2-bromo-2-methylpropane
C
1-bromopropane > 2-bromopropane > 2-bromo-2-methylpropane
D
2-bromo-2-methylpropane > 2-bromopropane > 1-bromopropane
검증된 단계별 안내1
Identify the type of alkyl halide for each compound: 1-bromopropane is a primary alkyl halide, 2-bromopropane is a secondary alkyl halide, and 2-bromo-2-methylpropane is a tertiary alkyl halide.
Recall that SN2 reactions proceed via a backside attack mechanism and are sterically hindered by bulky groups near the electrophilic carbon; thus, primary alkyl halides react faster than secondary, which react faster than tertiary.
Consider the nucleophile, Br⁻, which is a strong nucleophile favoring SN2 reactions, so the reaction rate will mainly depend on the steric hindrance around the carbon bonded to bromine.
Rank the compounds based on steric hindrance: primary (1-bromopropane) has the least hindrance, secondary (2-bromopropane) has moderate hindrance, and tertiary (2-bromo-2-methylpropane) has the most hindrance, slowing the SN2 reaction.
Conclude that the order of SN2 reaction rates from fastest to slowest is: 1-bromopropane > 2-bromopropane > 2-bromo-2-methylpropane.
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