Many mechanistic studies on the Wacker process have focused on pathway for formation of the C-O bond, the hydroxypalladation step. Henry inferred that coordinated hydroxide attacks the ethylene ligand, an internal (syn-) pathway. Later, stereochemical studies by Stille and coworkers support an anti-addition pathway, whereby free hydroxide attacks the ethylene ligand. The conditions for Stille's experiments differ significantly from industrial process conditions. Other studies using normal industrial Wacker conditions (except with high chloride and high copper chloride concentrations) also yielded products that inferred nucleophilic attack was an anti-addition reaction.