Aldol Reaction (Zimmerman-Traxler)

This animation of an aldol reaction between an E enolate and benzaldehyde demonstrates how the Zimmerman-Traxler transition state model explains stereochemical outcomes. The lithium metal coordinates to both oxygens, enforcing a rigid chair-like geometry.

1. The enolate and benzaldehyde form a chair-like transition state complex, with Li⁺ coordinating to both the enolate and carbonyl oxygen.
2. In the chair conformation, the bulky phenyl group preferentially adopts an equatorial position to minimize steric interactions.
3. The enolate carbon attacks the carbonyl carbon, forming a new C-C bond while generating an alkoxide ion.
4. Protonation of the alkoxide by acid yields the final β-hydroxy carbonyl product with anti stereochemistry.

The organized transition state explains why E enolates typically give anti aldol products. The reaction produces a racemic mixture since either face of the planar enolate can attack the aldehyde.