These reactions may have unexpected stereochemistry due to nearby lone pairs undergoing one of these reactions intramolecularly before a second one of these reactions occurs in a classic case of neighboring group participation. A pentacoordinate (*) transition state simultaneously forms and breaks a bond in a concerted (“con-SIR-ted”) reaction of this type that produces an inversion of stereochemistry through a backside attack. (10[1])Depending (10[1])on solvent and nucleophile, these reactions may compete with eliminations. (10[1])SN2 (“S-N-2”) and SN1 are nucleophilic mechanisms of, for 10 points, what class of reactions in which a functional group is replaced by another functional group? ■END■