When the compound shown below undergoes an S_N2 reaction with hydroxide, which of the following compounds will most likely form as the major product?

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11ecba2d_127a_b9ab_a3bf_c1b67b443427_MD0008_00 Substitution reactions require a good nucleophile and a good leaving group on a suitable substrate. S_N2 reactions occur when a nucleophile attacks an electrophile, causing the leaving group to leave in the same step. These reactions take place more readily on the less-substituted carbon because they are less sterically hindered, allowing the nucleophile easier access to attack the electrophilic substrate. Bromide and fluoride in the original compound are both primary alkyl halides, which are generally good substrates for S_N2 reactions. However, halide leaving group ability increases as the size of the halide ion increases because the increased ion surface area stabilizes the negative charge on the departing ion. The small size of fluoride makes it a poor leaving group (Choice B). Therefore, the attack by the hydroxide nucleophile will occur at the bromide site. Substitution of the bromide by the hydroxyl group forms a second -CH₂OH bonded on the central carbon, causing its chirality to be lost and yielding 2-chloro-2-(fluoromethyl)propane-1,3-diol. (Choices C and D) The chloride atom is tertiary, and therefore relatively unreactive. If chloride were to act as a leaving group, the backside attack associated with S_N2 reactions would cause a stereocenter inversion, changing the molecule to an S rather than an R configuration. Educational objective: S_N2 reactions are substitution reactions that occur when a nucleophile attacks the electrophile and causes the leaving group to leave in the same step. These reactions occur on the less-substituted carbon, and the halide leaving group ability increases as the size of the halide ion increases.

When the Compound Shown Below Undergoes an SN2 Reaction with Hydroxide

When the Compound Shown Below Undergoes an S_N2 Reaction with Hydroxide