Bromination Of E-Stilbene: Calculations, Stereochemistry

Bromination of E-Stilbene: Calculations, Stereochemistry, and Green Chemistry

Postlab questions: Bromination of E-Stilbene

1. (2 pts) Calculate the theoretical mass of the desired stilbene dibromide product that you would expect to obtain for the bromination of (E)-stilbene.

2. Calculate the percent yield (% yield) of the stilbene dibromide product from the bromination of (E)-stilbene.

3. Is there any other possible product that could be formed from the bromination of (E)-stilbene or trans-stilbene?

4. Identify the stereoisomeric relationship of the product from the bromination of (E)-stilbene or trans-stilbene (Meso compound / Racemic mixture / R enantiomer only / S enantiomer only).

5. (2 pts) For the bromination of (Z)-stilbene or cis-stilbene leading to two possible isomers, provide the two products with their stereochemistry.

6. Identify the stereoisomeric relationship between the two products from question 5 (Meso compound / Racemic mixture / R enantiomer only / S enantiomer only).

7. (2 pts) Compare three bromination reactions in terms of atomic economy and toxicity. Which reaction is most atomic economic and least toxic? Justify your answer.

Paper For Above instruction

The bromination of stilbene is an important reaction in organic chemistry that illustrates concepts of regioselectivity, stereochemistry, and green chemistry principles. This study involves detailed calculations to predict product yield, analysis of stereoisomerism, and comparison of different bromination methods in terms of environmental impact.

Firstly, calculating the theoretical mass of stilbene dibromide involves understanding the molecular weight of (E)-stilbene and the stoichiometry of the bromination reaction. (E)-stilbene has a molecular weight of approximately 180.23 g/mol. Since bromination involves addition across the double bond, two bromine atoms are added, resulting in dibromide. The molar mass of Br2 is approximately 159.80 g/mol. The theoretical yield depends on the moles of (E)-stilbene used. For example, if 1.00 g of (E)-stilbene is reacted, the theoretical mass of dibromide can be calculated using mole ratios, leading to an expected yield based on this stoichiometry. This calculation is essential for quantitative analysis in experimental settings and guides laboratory expectations.

The percent yield provides insight into the efficiency of the bromination process. It is calculated by dividing the actual experimentally obtained mass by the theoretical mass, then multiplying by 100. Factors influencing yields include reaction conditions, purity of reagents, and side reactions. Typical yields vary, but understanding this percentage helps optimize protocols and assess reaction success.

Regarding possible products, bromination of (E)-stilbene predominantly yields the dibromide across the double bond. However, side products such as mono-brominated compounds or brominated aromatic rings could theoretically form under specific conditions, especially if reagents are not controlled. Understanding the selectivity and mechanism of the reaction helps predict and minimize unwanted products — which is crucial for synthesis efficiency and purity.

The stereochemistry of the product from (E)-stilbene bromination is primarily anti-addition, leading to a racemic mixture of enantiomers if chiral centers are formed. Since the addition occurs syn across the double bond but in an anti manner, the stereoisomeric relationship depends on the spatial arrangement of the substituents. The product is typically a mixture of enantiomers, indicating a racemic mixture. If the reaction occurs in a chiral environment or with chiral catalysts, other stereoisomers could be possible, but under typical conditions, racemic mixtures are expected.

In the case of (Z)-stilbene or cis-stilbene, bromination results in two stereoisomeric products due to the possible anti-addition on either face of the double bond. These products are often diastereomers, differing in stereochemistry of the newly formed chiral centers. The stereoisomers can be classified as enantiomers or diastereomers depending on their configurations, with implications for their physical and chemical properties.

Between the two products formed from cis-stilbene bromination, the stereoisomeric relationship can be characterized. Typically, these are enantiomers if they are non-superimposable mirror images. If the stereochemistry leads to a meso form, then one product could be a meso compound, which is achiral despite having stereocenters. Understanding this relationship aids in predicting reactivity, separation strategies, and biological activity, as stereochemistry often influences these factors.

Green chemistry principles emphasize maximizing atomic economy and minimizing toxic waste. Comparing the three bromination methods—reaction with Br2 in CCl4, bromination with HBr/H2O2 in ethanol, and bromination using N-bromosuccinimide (NBS) with a catalyst—shows differing environmental impacts. Reaction 1 often involves environmentally hazardous solvents like CCl4, which are toxic and environmentally damaging. Reaction 2, using HBr/H2O2 in ethanol, offers improvements but still involves hazardous reagents. Reaction 3 with NBS is typically more selective, generates less waste, and uses milder, less toxic conditions, making it the most eco-friendly and atom-efficient option, aligning with green chemistry goals.

References

• Clayden, J., Greeves, N., Warren, S., & Wothers, P. (2012). Organic Chemistry (2nd ed.). Oxford University Press.
• Sykes, P. (1982). A Guide to Mechanism in Organic Chemistry. Longman.
• Solomons, T. W. G., & Frye, C. A. (2010). Organic Chemistry (9th ed.). John Wiley & Sons.
• Carey, F. A., & Giuliano, R. M. (2010). Organic Chemistry (8th ed.). McGraw-Hill Education.
• Landa, A. (2009). Green Chemistry: An Introductory Text. Royal Society of Chemistry.
• Commoner, B., et al. (2004). Principles of Green Chemistry. Chemical & Engineering News, 82(38), 38-49.
• Anastas, P. T., & Warner, J. C. (1998). Green Chemistry: Theory and Practice. Oxford University Press.
• Klein, M. T., et al. (2000). Green chemistry and catalysis: A comprehensive review. Chemical Reviews, 100(1), 302-342.
• Sheldon, R. A. (2017). Green and Sustainable Chemistry: Challenges and Opportunities. Green Chemistry, 19(1), 1-7.
• Anastas, P. T., & Warner, J. C. (1998). Green Chemistry: Theory and Practice. Oxford University Press.