Provide an FMO concept-based interpretation for the Wittig olefination reaction.

The Wittig Olefination reaction occurs in part 2 of our reaction. It results in the conversion of a carbonyl group into an alkene group. The first half of the reaction can be justified using frontier molecular orbital theory. The lowest unoccupied molecular orbital of the carbonyl group is attacked by the highest occupied molecular orbital of the Wittig reagent.  This reaction forms a four membered ring involving oxygen and phosphorus.  The ring is broken resulting in the formation of an alkene.