Provide the arrow-pushing mechanism for the reaction shown below.

Triphenylphosphine can be used to open epoxides via nucleophilic substitution. The initial substitution product (a betaine) quickly cyclizes to a 4-membered ring (oxaphosphetane) that collapses to triphenylphosphine oxide and an alkene. Draw the arrow-pushing mechanism for the reaction of trans-3,4-epoxyhexane and triphenylphosphine to produce hex-3-ene. Identify the specific stereoisomer of the product.

Determine an appropriate carbonyl compound and a Wittig reagent to form (Z)-5-ethylhept-3-en-2-one.

What is the primary significance of the Wittig reaction in organic synthesis?

Why does the Wittig reaction exhibit regiospecificity but not stereospecificity?