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Alkene Addition

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Lab 1: Alkene Addition


Lab 1 involved using experimental methods to determine and further understand the process of alkene addition, specifically through the bromination of (E)-stilbene. Within this process, a polarized electronic deficient bromine is added across an electron rich nucleophilic double bond, forming a three membered ring positively charged bromonium ion. The remaining bromide ion acting as a nucleophile attacks either side (top or bottom) of each carbon making up the double bonds from the opposite (anti) or same side (syn) of the positively charged bromonium ion ultimately opening up the ring system. The anti reaction results in a meso compound while syn addition forms the racemic product. In some cases a mixture of both meso and racemic products may result. The goal of this experiment was to identify the final favored intermediate product. Such a determination was made through comparison between experimental and known scientific literature regarding such properties as unique stereochemistry and melting point values for each possible product.


Experimental Details:

Reactants and Products MW (g/mol) Quantity (g or mL) Mass/MW (mol) Mp (C) Bp (C)

Acetic acid 60.05 4 mL 0.0666 16.5 118-119

meso-1,2-dibromo-1,2-diphenylethane 340.07 0.297 g (yield) 0.0009 (yield) 241 NA

Racemic-1,2-dibromo-1,2-diphenylethane 340.07 NA NA 113

pyridinium bromide perbromide 319.84 0.390 g 0.0012 135-137 NA

E-stilbene sample 180.25 0.2 g 0.0011 122-124 NA

pyridinium bromide perbromide observation addition produced cloudy deep orange color

Addition: methanol 2 1-mL portions, with excess

Final product white crystalized product


Theoretical yield:

(number mol -1,2-dibromo-1,2-diphenylethane = Mass of 1,2-dibromo-1,2-diphenylethane) / (MW of 1,2-dibromo-1,2-diphenylethane)

(0.0011 mol) x (340.07 g/mol )= 0.374 g meso-1,2-dibromo-1,2-diphenylethane

Percent yield:

Actual yield / Theoretical yield * 100

(0.297g) / (0.374g ) x 100= 79.41% yield of meso-1,2-dibromo-1,2-diphenylethane




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