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Leading Question: Develop a tutorial for your classmates on the Wittig reaction.

                   The Wittig reaction, seen in step 3 of the mechanism, allows alkenes to be produced from aldehydes or

               ketones using a phosphonium salt. This reaction involves three steps. First, the ylide (a compound with

               opposite charges on adjacent atoms) resonance contributor of the phosphonium salt attacks the

               carbonyl group of the starting material in a reversible reaction, forming a tetrahedral intermediate.

               Then, the negatively-charged oxygen atom attacks the positively-charged phosphorus atom, forming a

               four-membered ring. Finally, a ring-opening occurs, producing the products shown below.

Source:

“Wittig Reaction.” Organic Chemistry Portal. Web. 31 March 2015.

                                                       General Mechanism: