The stereochemistry of the elimination reaction of acyclic (E)-allylic acetates into the corresponding 1,3-dienes catalyzed by palladium in the presence of a base was investigated. The Z/E ratios of the resulting 1,3-dienes varied with the delta-substituents of the starting allylic acetates. This phenomenon was discussed based on the concept of a "syn-effect," which is most primarily rationalized by a sigma --> pi* interaction.