Bromination of an Alkene PDF

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Professor: Gita Venkatakrishnan...

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Bromination of an Alkene Abstract The purpose in conducting this experiment was to determine the more abundant product formed from three possible stereogenic isomers. This was done by performing a bromination of an alkene, in this case E-Stilbene, with pyridinium tribromide to produce 1,2-dibromo-1,2diphenylethane. The possible isomers which could form were the R and S isomers of the product in a racemic mixture and a meso compound. In this case, based on the stereochemistry of the molecule, the meso compound was hypothesized to be greatest abundance and was proved by analysis of IR spectrum gathered from the product. After conducting this experiment, 0.1888g of product was formed which was a yield of 50.1%, the melting point of the product was between 230 and 245 degrees Celsius, and the atom economy was calculated to be 67.6%.nu Post Lab Questions 1. Using the formula 2n where n is the number of stereogenic isomers, four isomers can be assumed. Two of them exist as a racemic mixture of 1,2-dibromo-1,2-diphenylethane and the other “two” are a meso isomer though it is counted only as one isomer because the compounds are superimposable on their mirror images. 2. The meso compound is most likely to be produced because of the stereochemistry being more favorable than the racemic mixture due to inhibition by the molecule. 3. The meso compound was produced and can be inferred from the IR spectrum analysis. 4. The atom economy for this reaction was 67.6% and this was found by dividing the molar mass of the desired product by the molar masses of the reactants. Discussion

Based on gathered data on the product formed by this reaction, it is within reason to say that the compound formed was meso-1,2-dibromo-1,2-diphenylethane. This is determined from the measured melting point range IR spectrum analysis. The melting point of the alkene reactant was 124 degrees Celsius while the melting point of the product was between 230 and 245 degrees Celsius which signifies a significant change. The IR spectrum also provides information supporting the change of the product as there is a C-H stretch at 2980.87 cm-1, indicating the presence of an alkane instead of the original alkene. Beyond this data, the percent yield and atom economy were also calculated for this experiment. These being 50.1% and 67.6% respectively. Sources of error in this experiment include loss of product while transferring vessels, insufficient or excessive amounts of heat when boiling the solution, and loss when vacuum filtering....