Discussion and Conclusion: Addition reaction of Alkenes: Bromination of (E)-Stilbene 1. Addition reaction is a reaction that involved two molecules that combine to make a larger product. Addition reaction has two main types, electrophilic addition and nucleophilic addition. An electrophilic reaction is when the pi bond of a molecule is removed to make two covalent bonds that are bonded to two new molecules. A nucleophillic addition is a reaction that removed the pi bond from a molecule and adds covalent bonds with two new compounds. Halogenation or most commonly known as bromination is a reaction that breaks a pi bond and adds a halogen or in this case, a bromine to the molecule.
This addition of the bromine can be very steroselective. Stereoselectivity can come from steric and electronic effects. Steric effect arise when two atoms ar brought close together, the resulting push of electrone clouds is what creates the significant change in shape. The steric and electronic chemistry affect the way the halogen react with the molecule. E-Stilbene is a hydrocarbon with a double bond and with phenyl groups attached to each side of the double bond in a such a way that the configuration is in the trans formation.
Stilbene has two isomers, tran stilbene, and cis stilbene, which is more unstable than trans stilbene. Z-stilbene has a melting point of 5-6 degrees C and E-stilbene has a melating point of 125 degrees C. The bromination of E-stilbene theoretically results in an all meso product. The mechanism suggests that when the bromine is attacked by the pi bond, it will add to on of the carbons. The other bromine adds to the other carbon but on the opposite side so that only the meso compound is made.
During the reaction the bridged halonioum intermediate is very important in desscussing the results in the actual experiment. Although the meso compound dominated because it is the most stable, the d/l compounds of stilbene...