Name: Date: Score: /72 INTRODUCTION TO ISOMERISM AND ALKENES EXERCISES 1. Draw the one constitutional isomer that is missing from column 1 of Model 1. (2 points) 2. Draw ten skeletal representations constitutional isomers missing from column 2 in Model 1 as you can. (Hint: Other than cyclohexane, there are 11 ways to draw a six-carbon backbone that contains a ring. Plus there are isomers of cyclohexane that do not contain a ring. ) (10 points) 3. Are any constitutional isomers missing from Column 3 in Model 1?
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A good way to answer this and similar questions is to start by drawing all possible carbon backbones. Then figure out how many different ways you can add the Br atom, or double bond. (3 points) 4. Draw as many constitutional isomers as you can with the formula C5H11F. (8 points) 5. Draw the structure of a six-carbon alkene (containing only C and H) with one ring and one double bond. (10 points) a. Draw a constitutional isomer of the structure you drew above with no rings. b. Explain the following statement found in many text books: “In terms of molecular formula, a ring is equivalent to a double bond. 6. Draw a skeletal representation of Z-2-hexene and E-2-hexene. (4 points) 7. Draw 1-butene. Why does it not make sense to specify either Z or E 1-butene while you must specify Z or E 2-butene to draw the correct molecule? (3 points) 8. Label each double bond E (trans), Z (cis), or neither. (It may help to draw in critical H’s. ) (4 points) 9. Label each double bond Z, E, or neither. (11 points) a. For each structure draw one constitutional isomer and all possible configurational stereoisomers. b. A “terminal” double bond is a double bond found at the end of a carbon chain (e. . , VIII and X). What generalization can you make about all “terminal” double bonds in terms of Z/E (or neither)? c. What is the relationship between Compounds III and IV above? 10. Name this molecule, draw and name its configurational stereoisomer, and construct an explanation for why naming this molecule using cis or trans (instead of E or Z) could lead to ambiguity. (4 points) 11. Draw another example of an alkene that cannot be named using the cis/trans nomenclature. (Such a molecule is not cis, trans or neither, but instead requires the E/Z nomenclature. (4 points) a. Draw the configurational stereoisomer of the molecule you drew above. (If it has no configurational stereoisomer, your original structure is not correct. ) b. Describe the characteristics of a molecule that falls outside the cis, trans or neither naming scheme and requires the E/Z naming scheme. 12. Double bonds do not rotate freely under normal conditions. The change from Z to E requires a reaction. This can occur in the presence of a catalyst or with the addition of a large amount of energy (e. g. , at high temperature). 4 points) One such reaction is diagramed below: (1) Add enough potential energy to break the double bond (Eact), (2) free rotation occurs at high energy transition state, then (3) reforming the double bond as a mixture of Z and E. Draw E-2-butene in one box and Z-2-butene in the other box, and explain your reasoning for the positioning of each compound. 13. Make up an example (not appearing in the previous activities) of a pair of molecules that are a) constitutional isomers, b) conformers, c) configurational stereoisomers. (6 points)
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