I think the first one is trans. But the second one could be either of the two, I

Question

I think the first one is trans. But the second one could be either of the two, I'm not sure. I need someone to explain this. What would happen for the slower molecule to react? And is it cis or trans that undergo E2 reaction faster? These are the full questions (picture below)

Thank you!

PostLab Questions: l. Review the bromination of an alkene sections in your lecture text. Based on the mechanism presented, use ChemBio3D to predict the product of this reaction. Your answer must include the ChemDraw structures (with stereochemistry labeled) and ChemBio3D models (proper viewing angle, please) for each diastereomer to support your prediction. CO2H CO2H CO2H H Br CH2Cl2 trans-Cinnamic Acid threo erythro Fisher Projections of the stereoisomers of 2,3-dibromo-3-phenylpropanoic acid 2. Use Chem3D to determine which one of the molecules shown below undergoes E2 reaction with NaOCH2CH3 in CH3CH2OH considerably faster than the other. (A review of cyclohexane conformations may be helpful.) Identify this compound and explain. Also, explain what must happen for the slower molecule to react. Be sure to include a printout of all relevant 3D structures (proper viewing angle, please) CH CH CH CH Br Br

Explanation / Answer

Ans 1) threo is the trans product and erythro is the trans product because in threo the functional group are on opposite sides and in erythro they are on the same side.

Ans 2) In the E2 mechanism, a base abstracts a proton neighbouring the leaving group, forcing the electrons down to make a double bond, and, in so doing, forcing off the leaving group. the hydrogen to be removed must be anti to that of leaving a group. Hence, the first molecule will undergo faster.

also to react the other molecule, E1 elimination mechanism can take place which depends on the concentration of substrate. the rate determining step is the formation of cation.Finally there is no requirement for the stereochemistry of the starting material; the hydrogen can be at any orientation to the leaving group in the starting material

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