Week_3_PurpleBook2007

Week_3_PurpleBook2007 - 59 Cyclohexanes Week 3 1. Look at a...

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Cyclohexanes 2. Draw each of the following dimethyl cyclohexanes (on the planar ring), then identify whether the substituents would be either: "Axial and Equatorial" or "Both Equatorial" 1,2-cis 1,3-cis 1,4-cis 1,2-trans 1,3-trans 1,4-trans 3. Draw each of the following in the most stable chair conformation: 1. Look at a chair. Notice the axial and equatorial substituents. Pay close attention to the parallel lines! Week 3 59
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CH 3 3 CH 3 CH 3 H H Bicyclic Compounds and Bredt's Rule 1. Draw each of the following bicyclic compounds in a good "perspective" drawing. 2. The molecule trans -cyclooctene is known to exist. (It is chiral, by the way). Why is the analagous molecule -cyclohexene unstable? = H H -cyclooctene (planar representation) -cyclooctene (perspective representation) H H -cyclohexene???? 3. Draw each of the following bicyclic alkenes in a good "perspective" representation. Only one of these three compounds actually exists. Which one, and why? Week 3 60
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1. Consider the following molecule: a) This molecule is expected to have two relatively stable "chair" conformations. Draw clear representations of the two different conformations in the boxes below. (The boxes have been arbitrarily labeled A and B .) In addition, please be sure to draw the isopropyl substituent in its best conformation in each case. b) Which of the two chair conformations is more stable? (circle one of the statements below) Chair Conformations CH 3 H 3 C CH 3 1) A is more stable than B. 2) Both conformations are equally stable. 3) B is more stable than A. Cl AB Week 3 61
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Principles of Reaction Stereochemistry 1. Each of the following statements is false . Discuss why the statement is false. Then make the statement true by changing only the u n d e r l i n e d word or phrase. Two molecules which are d i a s t e r e o m e r s should be expected to have the same melting point. Two molecules which are e n a n t i o m e r s would exhibit different rates of reactivity with an achiral reagent. An achiral starting material can react with an achiral reagent to give a s i n g l e c h i r a l p r o d u c t . Two molecules which are enantiomers would exhibit i d e n t i c a l reaction rates when reacting with a chiral reagent (such as a biological enzyme). When an achiral starting material is treated with an achiral reagent to yield a pair of d i a s t e r e o m e r s ,bo th products must always be produced in equal amounts. Week 3 62
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