3. Bromination of alkenes is an anti-addition; i.e. the substituents attach to their respective carbons on opposite sides of the plane of the molecule. Do they remain on opposite sides of the molecule after that? What are the absolute configurations of the carbons? Draw the product to illustrate your answers. CHM-251 Laboratory 7. Simamic Acid Bromination Rev 11-08|CHM-251 Organic Chemistry and Laboratory1/3CHM-251 Laboratory 7. Simami, Acid Bromination Rev 11-082/3Stereochemical results of syn and anti additionLahoratory 7, The Bromination of rans-Cinammic AcidRef. Modern Projects and Experiments in Organic Chemistry: Miniscale and Standard TaperMicroscale, 2" Ed, Jerry Mohrig, et al Freeman Press (2005), Experiment 16.2 pages139-142.Laboratory Objectives:1. Observe the bromination of an alkene as a representative addition reaction.2. Perform TLC methods development to determine an appropriate solvent system to separatereactants and products in an organic reaction.3.Use TLC as a means of determining how many products form in a reaction and as a methodfor determining if a reaction is complete.4. Examine how the anti stereochemistry of brominations can be observed in acyclic sytemsExperimental:Introduction:Bromination of Cinnamic Acid;The most common alkene reaction is electrophilic addition such that the double bond isreplaced by two sigma bonds. Electrophilic addition reactions include reactions with polarreagents such as HBr, polarizable molecules such as bromine, and the use of noble metal (På, Pt)catalysts with non-polar molecules such as hydrogen. In all addition reactions the products havemore atoms than the corresponding alkene. This laboratory will examine bromine addition to thedouble bond of cinnamic acid.Transfer trans-cinnamic acid (150 mg, 1.0 moles) to a 5.0 mL conical vial containing amagnetic stir vane (triangular stir bar) and combine with 1.5 mL of dichloromethane. Set in ansand bath and stir the mixture until the cinnamic acid dissolves. Add 200 µL of 1.0 M brominein dichloromethane solution and connect a condenser to the vial. Heat the reaction mixture untilthe dichlomethane, is refluxing. Once reflux has been achieved add four additional portions ofthe 1.0 M bromine solution waiting for the bromine color to disappear prior to each newaddition Monitor the reaction by TLC after the last addition and reflux for 10 minutes.cinnamic acid is still present by İLC then add an additional 50 µL amount of bromine. Onceyou confirm that cinnamic acid is no longer present cool the reaction to room temperature. If asubstantial amount of crystalline product is ahserread then cool the reaction and collect thecrystals by vacuum filtration rinsing with a small amount of hexane. Determine the meltingpoint of your sample and confirm that there is only one spot by TLC using the solvent mixtureyou determined for this separation. Compare your results to the expected products from syn andanti addition.. IfBromination of alkenes is a relatively straightforward reaction. Liquid bromine ishazardous in that it is corrosive and an oxidizing reagent. However, bromine is soluble in a.pumber of solvents and bromine solutions in water and in organic solvents reduce the hazards ofworking with bromine substantially. Cinnamic acid (structure below) will react with bromine togive 2,3-dībromo-3-phenylpropionic acid which is the product corresponding to the addition ofbromine across the double bond. EBARminations, exhibit trans stereochemistry which means thatthe bromines will be in a trans relationship if a cyclic alkene reacts. Cyclohexene would then beexpected to give trans 1,2-dibromocyclohexane as a bromination product. In the case ofcinnamic acid there is no ring to observe the trans positions of the bromines. Howerer the antiaddition of bromine can still be confirmed if we examine the stereochemical consequences ofthis reaction in greater detail. It turns out that the product of anti and syn addition arestereoisomers of one another but not in a cis trans sense. In this case we have an example ofdiastereomers (stereoisomers that are not mirror images of one another). The relationshipbetween cis and trans 1,2-dībromocyclohexane is also diastereomeric but obvious to us since wesee the bromines on the same or different sides of the ring. For cinnamic acid the two possibleisomers are less obvious but are called the meso' form and the D.L pair" (and both exist as a pairof mirror images or enantiomers). The designations treo, and entbro are also used todifferentiate these possible isomers which is based on the stereochemistry associated with thecarbohydrates (sugars) threose and erythose". In grder te see how these are different we willneed to carefully consider the 3-D relationships that result from both syn and anti addition.TLC Analysis:Using TLC to monitor a reaction is a common use of this technique. You will have to prepare amobile phase which is appropriate for your analysis. You should probably start with cinnamicacid and adjust the mobile phase such that the Rf is between 0.4 and 0.6. Co-spotting (placingthe reaction mixture with another authentic sample at the bottom of the plate) can be useful todetermine if cinnamic acid is the only compound present in your sample or to determine ifanother observed spot is or is not cinnamic acid.Techniques: 7.1, 15Note that you should have a reaction table with millimole amountsReference Information:Melting pointsDikxamocianamic, acid (2,3-dibromo-3-phenylpropionic acid)D.L pair or racemic mixture (2S, 3S) and (2R, 3S)Meso compound (2R, 3S) and (25, 3R)93-95 C202-204 "C.133-134 CCinnamic acid CHM-251 Laboratory 7. Simeic Acid Bitation Rev 11-083/3Questions:1. How many chirality centers are present in trans cinnamic acid? Does cinnamic acid existin any stereoisomeric form? If so how many stereoisomers are expected for cinnamicacid?2. Repeat question 1 for the product 2,3-dibromo-3-phenylpropionic acid.3. What would be the expected products if trans-cinnamic acid was treated with hydrogenand a catalyst (note typical conditions do not reduce aromatic rings)? Would you expectthe same number of stereoisomers from the hydrogenation reaction as you would in thebromination? Explain your prediction briefly.4. Draw the expected product from the anti addition (meso form) and its mirror image. Canyou show with structural representations that the mirror images are not identical(superimposable) to each other?5. If you reacted fumaric and maleic acid with bromine would be products be identical orwould the same stereochemical relationships found in cinnamic acid be present? Explainyour answer by drawing all of the expected stereoisomers for both of these acids (or ifnone are expected clearly show why with structural representations).Notes:1. Although meso may be used to descrībe the anti addition product this is actually pot thecorrect usage of meso. A meso structure has an internal plane of symmetry and will notexist as a pair of enantiomers. In the case of the product of cinnamic acid you may seethe meso designation to mean that it is "meso like in that it would be meso if the alkenewas symmetrical. The more corect way to describe this pair of enantiomers is to use thecorrect absolute configuration and describe these as the RS and S,R enatiomera oftenwith the carbon atoms that are chirality centers identified by number.2. In a structure with two chirality centers DL is often used to represent the RR and S,Spair of enantiomers. You also may see the identifier as racemic or +- used Áll of theserepresent the case with two stereoisomeric structures which exist as a racemic pair. Theuse of any of these designations is used generally to represent a racemic mixture hut inthis case also specifically differentiates the structures that would be racemic even if thealkene was symmetrical.3. There is a great deal of historical connection between stereochemical designations andcarbohydrates.glyceraldehyde which is a three carhon sugar and the simplest sugar with a chiralityThe tems D and L are linked to the enantiomeric forms ofcenter.Threose and Erythrose are the sugars with the one more carbon thanglyceraldkude. The more general designation of etoro, and threo, to describe the twodiastereomers arising from two chirality centers indicates one isomer as having the twosimilar groups on the same side in a Fischer projection (called eythe-) and the other withthe groups on opposite sides (called threo). This corresponds to the structures ofexthose and threose as found in the McMury text in Figure 25.3 (or equivalent).4. Note that in the structures provided here that the positions of the phenyl group and theacid group remain in the same relative orientation as they are found in cinnamic acid.This allows the positions of the bromines to be compared directly as anti and syn.Recognize that each structure has many possible representations resulting from rotationaround the C2-C3 bond.

Here in this case ,we are taking example of bromination of cinnamic acid ,and how much chiral centre…

Answered: Bromination of alkenes is an…

Chemistry

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Chapter1: Chemical Foundations

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Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...

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