ABSTRACT
The important properties of conjugation include the interaction of conjugated molecules with ultraviolet light and the changes in chemical reactivity that are induced, relative to unconjugated molecules. A suprafacial shift is when the σ-bond to the hydrogen atom is made and broken on the same side of the conjugated system. An antarafacial shift is when the σ-bond is broken on one side of the conjugated system but made on the opposite side of that system. The functional groups that best accept a photon of ultraviolet (UV) light are those that contain a conjugated π-bond or a polarized π-bond. Simple alkenes do not absorb UV light effectively, but conjugated dienes and conjugated carbonyls give strong absorption bands in the UV. The interaction of the π-bonds in the conjugated diene makes absorption of the light easier, accounting for the difference in absorption maxima.
