Question
Which of the following is not a characteristic of SN2 reactions?(A) the electrophilic carbon undergoes inversion of stereochemistry(B) the rate is proportional to the concentration of substrate(C) the rate is proportional to the concentration of nucleophile(D) the rate is independent of the solvent
Answer
(D), solvent-independent rate, is NOT an SN2 characteristic. The original question asks for the exception. If you are selecting the valid properties from this same set, they are A, B, and C.
| Option | Verdict | Reason |
|---|---|---|
| A: inversion at the electrophilic carbon | True | Backside attack inverts the local tetrahedral arrangement. |
| B: rate proportional to substrate concentration | True | At fixed conditions, rate = k[substrate][nucleophile]. |
| C: rate proportional to nucleophile concentration | True | Both partners participate in the single substitution step. |
| D: rate independent of solvent | False | Solvation changes nucleophile availability and the activation barrier. |
SN2 is concerted: bond formation and bond breaking occur in one step without a carbocation intermediate. Polar aprotic solvents often accelerate reactions involving anionic nucleophiles relative to protic solvents. The solvent changes k, even though it is not shown as a concentration factor in the elementary rate law.
Evidence boundary
This is Georgia Tech Quiz 6-2, question 8, which asks which property is NOT characteristic. D is the single answer to that prompt; A, B, and C are the valid properties. Rate comparisons hold temperature, solvent, and other conditions fixed. Inversion describes geometry at the reacting carbon, not a guarantee that an R/S label changes when substituent priorities change.
Sources
These references support the concepts and methods used in the explanation above.