Which energy diagram best represents an $S{N}_2$ reaction?

• A. Two distinct energy maxima separated by a reaction intermediate.
• B. A single transition state with one energy maximum and no intermediate.
• C. Multiple energy minima corresponding to several intermediates.
• D. A flat energy profile with no transition state.

Answer: (B)

Verified step by step guidance

1. Understand that an SN2 reaction is a bimolecular nucleophilic substitution that proceeds via a single concerted step without intermediates.
2. Recall that the energy diagram for a reaction shows the energy changes as reactants convert to products, with peaks representing transition states and valleys representing intermediates.
3. Since SN2 reactions proceed through a single transition state, the energy diagram will have one energy maximum corresponding to this transition state.
4. There are no intermediates in an SN2 mechanism, so the diagram will not have multiple energy minima between reactants and products.
5. Therefore, the correct energy diagram for an SN2 reaction is one with a single peak (one transition state) and no intermediate valleys.