Bromination Of Trans-Cinnamic Acid And Trans-Stilbene.

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Bromination of trans-cinnamic acid and trans-stilbene
Determining how a mechanism takes place is crucial in order to define a mechanism. In this experiment, a mechanism was determined based on the purified product’s melting point. This was accomplished by comparing the acquired melting point with the one provided by Professor Link. (Q1) When 0.252 g of trans-cinnamic acid was mixed in 2.5 mL glacial acetic acid and introduced to 0.434g pyridinium tribromide, the resulting product reflects an addition reaction. In general, reactions take place to achieve its lowest Gibb’s free energy because it’s at this point where a structure is most stable; in this case, the reaction is an addition of bromine into alkenes. (Q2)
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The melting point range was close to the anti structure, but because it was a widened range it is speculated that the syn structure was also present. (Q9) However, this does not mean the other mechanisms are completely discarded. Upon recrystallizing the pure product, a gross mistake potentially skewed the results; non-DI water from the ice bath was introduced to the crystallized product by mistake. Recrystallization of the pure product was redone, but random ions from the ice bath could have infiltrated the crystal lattice of the pure product thereby widening the melting range. Also, the melting range could have been affected by the temperature intervals used; time was running out and the Digi-Melt was programmed to increase in intervals of 10°C instead of 5°C. This could have affected the melting range observed significantly; slow and steady probes to be a better method. (Q10) Both the percent yield (106.5%) and recovery (54.75%) are not ideal numbers; ideally, percentages should be close to 100% but not over or under. As mentioned above, (in Q9), a gross mistake occurred where non-DI water got into the pure product as it was recrystallizing; the flask’s buoyancy caused it to tip over and the non-DI water from the ice bath got inside the pure product. This affected the data as electrolytes from the ice bath could now be part of the crystal lattice of the pure
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