all of the following alkyl bromides react by sn2 substitution when treated with sodium cyanide. which one does not undergo an inversion of configuration? a. (s)-2-bromo-3-methylbutane b. (r)-1-bromo-3,3-dimethylcyclohexane c. (r)-1-bromo-2-methylbutane d. cis-4-ethyl-1-bromocyclohexane