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CHEM 20 Midterm: Practice-Exam-1C

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turquoisegnu128

9 Jan 2019

School

Harvard University

Department

Chemistry and Chemical Biology

Course

Professor

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Document Summary

Important notes: this exam consists of 8 problems on 8 pages, plus this cover sheet, and one page for scratch work at the end of the exam, all answers must be written in the spaces provided. Answers written on the back of a page will not be graded. Anything written on the scratch page will not be graded: you are allowed to use a set of molecular models for this exam. Name: each of the following transformations can be carried out in one or two steps. Fill in the reagents required for each step. If a second step is not needed, please put an x through the second box. a) b) c) d) Name: fill in the boxes with either the reactant or the product (as appropriate) of each of the indicated transformations. Be sure to indicate the stereochemistry if it is relevant. a) b) c) c: o3, h2o2.

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Related Questions

This is a practice test and I really need help figuring out what reactants produce this products. I am not sure if I am correct on the first one but I tried to draw a secondary alcohol producing a ketone via oxidation. Any help would be greatly appreciated.

questions 12-21

STEREOISOMERISM WITH MOLECULAR MODELS models regularly in your courve to view three-dimenstional structures as an aid to predicning behavior and reactivity. This exercise is dexigned to familiarize you wih stereaisomerism.As you build the madlels insdractor for credit befare leaving Your instractor may provide a key below, questians are posed that you should answer in your notebook You will need to show your work to your Enantiomers and Diastereomers Review the definitions of chirality center, enantioners, diastercomers, meso, and the symmetry elements (plane, axis, and center of symmetry). A chiral molecule cannot have a plane of symmetry, a cester of symmetry or an axis of symmetry greater than two-fold (i.e, mo less than 180Â° rotation). Leaming to recognize these clements, or the lack of them, is a skill best developed with models 1. Build a model of a tetrabedral carbon with three iferent grours atachod. (For consistency with thesc instructions use black, red, and two green atoms for these groups and use bonds of all the same length.) What elements of symmetry does this model have? 2. Is this model chiral 3. Build a second model that is a miror image of the first Compare the models; are these models superimposable? . If these models were actual molecules, how would you descrihe the relatiorship between them? S. Replace one green atom on each model with a blue atom such that they are mitror images of each other. What elements of symmetry do the models have 6. Are the models saperimposable? 7. Are the models chiral? 8. How would you describe the relaionship between molecules represented by these models? 9. Use the two models you have already built for this exercise. Exchange the pasitions of the green and blue aboms on on of the models so that the two models are now ideutical (superimposabile) Remove lbe black substituent from each model and join, with a single bond, the two carbons that still ave three substituents on each. How many chirality ceaters does this model have? 10. What elements of symmctry does this model bave? 11. Is the molecule chiral? 12. Construct a mirror imnge of the last model made and then cormpare the two models. Are the models 13. If these models were actual molecules, bow would you describe the relaionship between them? 14. Can one enantiomer be chiral and the other achiral? Why or why not? 15. Take gnc of the two models you have alrcady built. Switch the positions of the green and hlue substitvents that are attached to the saue carbou;, leave the other carbon unxbainged Now compare the two modcls again. Are the models still stcreoisomers? 16. Are they mirror images? 17. If these models were actual molecules, how would you describe the relationship between theu? 18. Now focus on the one model whnse substituents you switched. Does this model have any chirality centers How many? 19. What elements of symmetry does this model have? 20. Is this model chiral? Explain why or why not. 21. Draw a dash-wedge reprscntation of this model in both an clipsed and a staggered conformation, as shawn. Assume that red oxygen, green chlorine, blue nitrogen, and black cabon. Identity any chiral centers with an astcrisk. Rank the substituents on each chirality cente and assion each chirality center its correct sbsolute configuration (R or S) Staggered Organic Chemistry Leb Masual Harper College, Fall 2010 Eclipsed