B. (2 pts) The regiochemistry of alcohol dehydration is determined by the: a. Zaitsev rule; b. Hammond postulate;

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1 CEMISTRY MIDTERM # answer key ctober 1, 008 Statistics: Average: 73 pts (73%); ighest: 98 pts (98%); Lowest: 3 pts (3%) Number of students performing at or above average: 36 (58%) Number of students performing at or below 55%: 11 (18%) Number of students performing at or above 90%: 14 (3%) 1. (9 pts) Mark as true (T) or false (F) the following statements. Do not explain! (T) Free-radical bromination is more selective than free-radical chlorination; (T) Tertiary radicals are the most stable radicals; (T) Free radicals are electron-deficient species; (T) E1 and S N 1 reactions are both stepwise processes; (F) Carbocations are formed in S N 1 reactions but not in E1 reactions; (T) More substituted alkenes have lower heats of hydrogenation; (T) ydrogenation is always a syn-addition process; (F) Trans-cyclopentene is more stable than cis-cyclopentene; (T) ydroboration-oxidation yields an anti-markovnikov product;. Circle ALL that apply: A. ( pts) E elimination reactions are characterized by a. Use of strong bases; b. Stereoelectronic effects; B. ( pts) The regiochemistry of alcohol dehydration is determined by the: a. Zaitsev rule; b. ammond postulate; C. ( pts) Free-radical bromination: a. ccurs via carbocation; b. Is a chain reaction; c. Formation of carbocations; d. Rearrangements; c. Markovnikov rule; d. Lewis octet rule; c. Requires an initiation step; d. ccurs fastest at primary positions; 3. (3 pts) Provide an acceptable name for each of the following molecules: 3-vinylcyclopentanol trans-cycloheptene methylenecyclohexane 4. (4 pts) Provide the structural formula for each of the following molecules: I vinylcyclopropane allyl iodide (Z)--bromo--pentene Trans-1,-dibromoethylene 5. (5 pts) Assign E or Z configuration to each of the following compounds. D NT name the compounds! C 3 N C C(C 3 ) 3 N N Z E E Z Z F

2 6. (6 pts) For each of the following species, complete the Lewis structure and provide two additional valid resonance forms. Use the curved arrow formalism to show the flow of electrons. Rank the resultant resonance structures. N N N N N N 1 3 maximum # of bonds no incomplete octet at N maximum # of bonds 1 3 same # of bonds as 1 but charge on a less electronegative center fewer bonds, greater than 1 or 7. Consider isomeric pentenes (C 5 10 ). A. (5 pts) Draw the structures of all isomers. Indicate the isomer, which you would expect to be the most stable. most stable B. (6 pts) For the most stable pentene isomer: a. Write the equation and predict the structure of the product(s) of acid-catalyzed hydration; 3 b. Write the equation and predict the structure of the product(s) of hydroboration-oxidation; 1. B 3.TF. / - c. Write the equation and predict the structure of the product(s) of reaction with chlorine in water;

3 8. (4 pts) Predict the principal organic product(s) in each of the following reactions. Draw the correct stereoisomeric product, wherever applicable. 3 hν, Δ hν C 3 Δ RR 3 P 4 heat C 4 NaC C 3 1) B 3.TF C 3 C ) / - MCPBA C 1) 3 ) (C 3 ) S 9. Suggest an appropriate set of reagents/conditions and write an equation for each of the following transformations: A. ( pts) Propane to -bromopropane; hν, Δ B. ( pts) Cyclohexanol to cyclohexene; S 4 Δ C. ( pts) 1-pentene to -pentanol; D. ( pts) 1-pentene to 1-pentanol; 3 1. B 3.TF. / (4 pts) Acid-catalyzed dehydration of,-dimethylcyclohexanol produces 1,-dimethylcyclohexene as the major product. Write an equation and suggest a mechanism to explain this occurrence. 3 methyl shift - - 3

4 11. (4 pts) Suggest a DETAILED mechanism for the following reaction. 3 C 3 C 3 3 C 3 C C 3 1. (6 pts) Suggest synthetic sequences (more than one reaction!!) for the following conversions. Use any necessary organic or inorganic reagents. A. Chlorocyclohexane to trans--bromocyclohexanol; NaC 5 C 5 B. Isobutyl iodide to t-butyl chloride. I NaC 5 C (4 pts) The two isomeric structures given below behave very differently when reacted with NaC 3 /C 3. Compound 1 yields a single product of elimination, while does not react at all. Provide a detailed structural rationalization for these facts and draw the structure of the product of elimination derived from 1 (No lengthy verbal explanations please! More structures, fewer words!). C 3 C 3 C 5 C 5 1 C 3 C 3 C 5 1 C 3 C 5 NaC 3 C 3 C 5 this hydrogen and chlorine are anti-coplanar and can be eliminated C 3 there are no β-hydrogens that are coplanar to chlorine. E elimination cannot occur C 5 C 3 C 5

5 14. (3 pts) Draw all constitutional isomers formed by monochlorination of the following alkane with /hν: 15. (3 pts) Among the isomers of pentane (C 5 1 ), identify the structure that yields a single product of monochlorination. Isomers of C 5 1 : hν 16. ( pts) BNUS PRBLEM (In order to receive credit for this problem, it has to be solved entirely!!). When cyclohexene is allowed to react with bromine in an aqueous solution of sodium chloride, the following products are obtained: trans-1,- dibromocyclohexane, trans--bromocyclohexanol and trans-1-bromo--chlorocyclohexane. Suggest a detailed mechanism that accounts for the formation of ALL three products. Na -