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Lecture 5

BCH 119S Lecture 5: Lab 5 stilbene

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BCH 119S

Systematic Investigation of the Synthesis of stilbene dibromide Through bromination of E-stilbene Raven Cortright †*Conrad Fjetland †* †Department of Chemistry and Biochemistry, University of Texas, 1 University Station, Austin, TX 78712 *[email protected] Introduction The purpose of this lab was to react Br2 and E-stilnene to obtain stilbene dibromide. The pi bond in the E-stilbene attacks as a nucleophile to create a carbocation intermediate that reacts witht the bromine atoms to form stilbene dibromide. Once the product was made, it was vacuum filtrated, recrystilized, and a melting point was taken. The melting point was a test to insure purity and proper stereochemistry of the desired product. The main reaction is shown below. Because the reaction is not stereospecific, the products are mixed with D and L enantiomers. Certain conditions are required for this reaction to proceed. E-stilbene, the trans ethylene isomer, attacked nucleophilicaly the Br2 to create the carbocation intermediate and bromine anion. The bromine anion then bonds to the carbon to form stilbene dibromide.Alkenes are fairly reactive, making them very important in synthesis. Pi bonds are weaker than sigma bonds and is energetically favorable for pi bonds to attack in electrophilic addition reactions. Meso-stilbene dibromide is the isomer that is most likely, more likely than the diastereomer. During the formation of the carbocation intermediate, the attack can occur in two forms. An acylic intermediate can be formed when the bromine bonds to a just one carbon, which results in a .If both bromines bond to the carbons of the alkene, a cyclic intermediate is formed instead which results in a meso compound. Depending on the attack, the carbon or the bromine will have the positive charge. Bromination of E-stilbene is actually considered non stereospecific because it results in both meso and the D, L enantiomers. The meso product is predicted when the cyc
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