Question

Part A: Molecular Modeling 1. Models of 1,2-Dibromoethene Br, H Br Br C= C H Br trans-1, 2-dibromeoethene cis-1, 2-dibromoethene A (trans) B (cis) Figure 7.2. Geometric Isomers. Procedure Part A Construct a model of 1,2-dibromoethene (CHBr=CHBr) so that if viewed from above and in front, see Figure 7.2. Answer all questions on report sheet. 1. Are the models superimposable? 2. Are A and B stereoisomers? Are they enantiomers or diastereomers? 3. Name A, use the E-Z system. 4. Name B, use the E-Z system. 5. Without breaking bonds, try to convert A to B, what prevents A from being converted to B? 6. How could A be converted to B by breaking only one bond? Replace one bromine atom with a hydrogen atom in each model. 7. Are the models superimposable now? 8. Name the molecule they represent. 9. What is there about this molecule that prevents it from showing cis-trans isomerism? 10. What structural feature is necessary if an alkene is to exist in cis and transforms? 11. Indicate which of the following substances can exist as cis-trans isomers: 1-chloropropene, 2-chloropropene, 1-pentene, 2-pentene. Show these structures.
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Answer 1

Find the model in attached image file. Answers are given here

1. No the models are not superimposable.

2. A and B are stereoisomers as they occurs in space or three dimensionally. No, they are neither enantiomers nor diastereomers. They are geometrical isomers not optical.

3. E-1,2-dibromoethane.

4. Z-1,2-dibromoethane.

5. Without breaking bonds no one can convert A to B or vice versa. A and B are configurational isomers which can only be interchanged by breaking and making bonds. The presence of double bond between carbon prevent the phenomena.

6.A can be converted to B if we break any of C=C double bonds. Then both the carbon attached in single bond and so rotation in bond possible. If rotation in C-C axis possible we can convert structure A to B.

7. No, the models are still not superimposable.

8. Now the molecules represent single structure which will be Bromoethene or 1-Bromoethene.

9. The same substitution single carbon prevents them to posses cis-trans isomerism. If there is two H substitution in single C then it cannot show geometrical isomerism.

10. For cis trans isomerism there should be same group in different double bonded carbon that means structure should be like Cab=Cab.

11. No structure can posses cis-trans isomerism. Find the structures in attached image file.

Part A - Above view trans- esomer. isomer k front view, CH3 De=chce -Chloro propene te - G=CH₂ He=CH-CH₂ - CH₂ - CH3 - pentene 2-chbro propene HC-CH=CH-CH₂ - CH3 32- Pentene. ce