The aldol reaction is stereospecific and proceeds via the Zimmerman–Traxler transition state depicted below.
(a) Illustrate the arrow-pushing mechanism for step A and step B.
(b) Explain why this mechanism is favorable.

• A. This mechanism is favored because the chair-like transition state increases system entropy and metal chelation only stabilizes the reactants.
• B. This mechanism is favored because the boat-like transition state lowers the activation energy but metal chelation has no effect on stability.
• C. This mechanism is favored because the chair-like transition state raises the activation energy and metal chelation destabilizes the intermediate.
• D. This mechanism is favored because the chair-like transition state lowers the activation energy and metal chelation provides additional stabilization.

Answer: (D)