
Which of the following statement(s) about the SN1 mechanism is/are correct?
I. The transition state contains a pentacoordinate carbon species
II. The “1” in SN1 indicates a that the mechanism involves a single reaction step and exhibits second-order kinetics
III. This reaction mechanism is characterized by partial or complete racemization at a stereogenic reaction center and exhibits first-order kinetics
IV. This reaction mechanism is favored by tertiary substrates

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Correct Answer: B. III and IV
Statements II and IV can be associated with the SN1 mechanism. Statement II is incorrect: the “1” in SN1 refers to the fact that the reaction operates under first-order kinetics (substitution, nucleophilic, unimolecular); that is, the slow (rate-determining) step is leaving group dissociation. Statement I describes the SN2 mechanism (backside attack, simultaneous nucleophile attack and leaving group dissociation).
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