Dehydrohalogenation of meso-S tilbene Dibromide: Diphenylacetylene You will be p

Question

Dehydrohalogenation of meso-Stilbene Dibromide: Diphenylacetylene

You will be performing a standard E2-elimination reaction. The product you formed the previous week contains 2 bromides, which we know to be good leaving groups. In the presence of a strong base, such as a hydroxide base (OH-) or NaNH2, a proton on an adjacent carbon to the bromide will be removed. This deprotonation pushes the electrons that were formerly in the CH bond to form a carbon-carbon double bond. Since meso-stilbene dibromide contains two bromides, this process occurs twice leading to a triple bond. This reaction is stereospecific as it requires that the leaving group and the proton be anti-periplanar to one another. Double dehydrohalogenations are useful reactions for the synthesis of alkynes. The vicinyl halide could be isolated if a molder base is used or the reaction is run at lower temperature. High heat is required to obtain the alkyne due to the second elimination occurring via a syn pathway which has a much higher barrier than the anti pathway.

how can I write summary and anaysis using my date

my mp is 59-62%which is clsoe to diphereylacetylene melting point

percent yield is 20%   

Explanation / Answer

1,2-dibromo-1,2-diphenylethane/ meso stilbenedibromide on reaction with Base such OH- or NH2- which induced elimination of HBr via one- step concerned mechanism given 1-bromo-diphenylethene at low temperature while heating second dehydrohalogenation yield diphenylacetylene. It is stereo specific reaction.

While the melting point is 59-63 oC which is closed to diphenylacetylene with 20% yield.

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