I need help with questions 1-4. I added pictures of the entire lab for backgroun

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I need help with questions 1-4. I added pictures of the entire lab for background. In question 1, I'm now sure how you would be able to distiguish between the mechanisms. Would it involve the IR spectrum? In question 2, I'm not sure why. I just know not to calculate it with bromine. Is it because bromine is the catalyst? 3 & 4 not sure how to answer.
I have tried to teach myself to understand and asking my professor but he is no help. Experiment 13: Bromination of (E)-Stilbene Determination of the Stereochemistry of Addition Reading from Klein: Chapter 9, Section 8. Reaction: Br2 CHyC½ (Stereochemistry to be determined) IMPORTANT! Do the pre-lab exercises on page 69, writing come to lab. your answers in your notebook, before yotu Introduction and background Chemists who study reaction mechanisms classify them in a number of ways.A reaction reaction is regioselective if a the other could theoretically produce two or more constitutional isomers, but only one is the major prode example, treatment of 1-hexene with HCI produces only 2-chlorohexane. Little to no possible isomeric product, is formed stereospecificity. A stereospecific reaction is one where r stereolsomeric products, For example, hydrogenation Another term used to describe chemical reactions is of an alkene is stereospecific. If one carries out the hydrogenation of 3-m (25,3 ethyl-2-phenyl-2-pentene, the are obtained depend on whether the (Z) or (E) isomer is used. If the (2) isomer is used, the y alkane products are the (25,35) and (2R3R) isomers. On the other hand, if the (E) isomer is used, then the R) and (25,3R) isomers are the only products formed. Therefore,this reaction is completely stereospecific. The hydrogenation of alkenes is a stereospecific reaction. H2 CH CHs catalyst(2535) (253s) plus (2R,3R) (ZD-isomer CH H2 catalyst (25,3R)plus (2R,3S) In this experiment, you will carry out the bromination of (E)-stilbene (1 2-diphenyl-ethene). The product 1,2-dibromo-1,2-diphenylethane, is also known as stilbene dibromide. The product has two stereocenters, and there are three possible stereoisomers: (IR2R), (IS25) and (lR25). Note: only three isomers are possible because the (1R 25) and (1S2R) compounds are actually the same has an internal plane of symmetry, making this isomer a meso compound. Four possible mechanisms for the addition reaction are suggested on the next page. You will identify the product(s) of the bromination reaction and then use this information to determine whether the bromination reaction is stereos whether the reaction proceeds via syn or anti addition. (E)-isomer substance: a meso compound. The structure and if it is

Explanation / Answer

1.  It can be determined experimentally. It is either Mechanism 1 generated to a high mixture or formation of products or Mechanism 4 gave the mixture of the product.

Temperature or catalyst could also be another factor.Some temperatures or catalyst may service the mechanism and vice versa.

2.  Because the addition or elimination of bromide didnt disturb the mechanism. This time the bromide is acting as a spectator ion or reactants.

Shortage or excess of it wouldnt bring any change. The reaction is going to be the same as it was before unless otherwise stated.

3. The student will obtain dibromostilbene. The addition of bromine is another widely-used reaction.

4. Meso Compounds. This is because, it contain two or more equal substituted stereocenters.

It has an internal symmetry plane that divides the compound in half. These two halves reflect each other by the internal mirror. The stereochemistry of stereocenters should "cancel out".

This means, when we have an internal plane that separations the compound into two symmetrical sides, the stereochemistry of both left and right side should be opposite to each other, and therefore, result in optically inactive. Cyclic compounds may also be meso.

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