text: The stereoelectronic effect influences the thermodynamics of equilibrium. For example, the following equilibrium could be achieved via a cascade of pericyclic reactions.
  Despite very similar structures, one of the two isomers is strongly favored over the other because of a stereoelectronic effect. Since the σ* orbital adjacent to the electron-withdrawing carbonyl group is lower in energy and is therefore a better acceptor than the σ* orbital adjacent to the methoxy, the isomer in which the n lone pair is able to donate into this lower-energy antibonding orbital will be stabilized (orbital interaction illustrated).
  Another example of the preference in the equilibrium within the area of pericyclic reaction is shown below. The stereoelectronic effect that affect the equilibrium is the interaction between the delocalized “banana bonds” and the empty p orbital on the boron atom.