In the bromination of stilbene experiment, trans-stilbene (E-stilbene) is used. If cis-stilbene (Z-stilbene) was used, would the product be an enantiomer or diastereomer of the product obtained with trans-stilbene. Explain why.ÂÂ
q1. In the bromination of stilbene experiment, trans-stilbene (E-stilbene) is used. If cis-stilbene (Z-stilbene) was used, would the product be an enantiomer or diastereomer of the product obtained with trans-stilbene. Explain why.ÂÂ
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q2. If the literature melting point of the product in the bromination of stilbene (trans-stilbene + Br2 in cyclohexane) is 239-241oC, and a student obtained a melting point of 229-233oC for their product when carrying out the experiment, what conclusion can be drawn.
q3. In the bromination of stilbene when adding the cyclohexane why does the product precipitate out of cyclohexane?
The Correct Answer and Explanation is :
q1. In the bromination of stilbene, using cis-stilbene (Z-stilbene) instead of trans-stilbene (E-stilbene) would yield a product that is a diastereomer of the product obtained with trans-stilbene. This outcome arises because the stereochemistry of the starting material influences the stereochemistry of the product. When trans-stilbene undergoes bromination, it predominantly forms meso-stilbene dibromide, a compound with a plane of symmetry and no chiral centers. In contrast, bromination of cis-stilbene leads to a racemic mixture of enantiomers, as the addition of bromine occurs in an anti fashion, resulting in two non-superimposable mirror images. Therefore, the product from cis-stilbene is a diastereomer of the product from trans-stilbene. (ChemEurope)
q2. If the literature melting point of the product in the bromination of stilbene is 239-241°C, and a student obtained a melting point of 229-233°C, it suggests that the product is impure. Impurities typically lower and broaden the melting point range of a compound. The observed melting point is lower than the expected range, indicating the presence of contaminants. To confirm the identity and purity of the product, the student should consider purifying the compound through recrystallization and re-measuring the melting point. (Rose-Hulman Institute of Technology)
q3. In the bromination of stilbene, the addition of cyclohexane serves as a non-polar solvent that helps in the precipitation of the product. The product, 1,2-dibromo-1,2-diphenylethane, is less soluble in cyclohexane than in the reaction mixture, leading to its crystallization upon cooling. This precipitation facilitates the isolation of the product from the reaction mixture. The use of cyclohexane also aids in washing away soluble impurities, thereby enhancing the purity of the final product. (Boston College)