Stilbene generally comes in two possible stereoisomers: cis and trans. When reac

Question

Stilbene generally comes in two possible stereoisomers: cis and trans. When reacted with bromine, the trans isomer makes two enantiomers, which are superimposable diastereomers of the same form, meso. The cis form makes another mixture with two non-superimposable structures which have very different properties compared to the meso mixture.

a) Would the mixture containing the meso form have a specific melting temperature or a mixture of temperatures?

b) What is the name of the type of differential mixture formed from the cis form where the compounds are not superimposable but are present in equal amounts?

c) How could you differentiate whether you had the cis or trans form as your starting material (give at least one example of a technique you could use):

Explanation / Answer

a, The mixture containing the meso form have specific melting poing.

b, It is called a racemic mixture, because it has equal amount of the two enantiomers.

c, By comparing NMR coupling constants. Cis and Trans alkenes have different coupling constants. Cis (6-14 Hz) and Trans (11-18)

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