3. (6 pts) Provide an acceptable name for each of the following molecules: OH

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1 CEMISTRY MIDTERM # 2 answer key June 07, 2005 Statistics: Average: 71 pts (71%); ighest: 99 pts (99%); Lowest: 45 pts (45%) Number of students performing at or above average: 15 (48%) 1. (11 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 carbocations are most stable; (T) Tertiary radicals are most stable; (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 s of hydrogenation; (T) ydrogenation is always a syn-addition process; (F) E-isomers are always more stable than Z-isomers; (F) Trans-cyclopentene is more stable than cis-cyclopentene; (T) ydroboration-oxidation yields the anti-markovnikov product; 2. Circle ALL that apply: A. (3 pts) E2 elimination reactions are characterized by a. Use of strong bases ; b. Stereoelectronic effects ; c. Formation of carbocations; d. Rearrangements; B. (3 pts) The regiochemistry of alcohol dehydration is determined by the: a. Zaitsev rule ; b. ammond postulate; c. Markovnikov rule; d. Lewis octet rule; C. (3 pts) Free-radical bromination: a. ccurs via a polar mechanism; b. Is a chain reaction; c. Requires an initiation step; d. ccurs fastest at primary positions; 3. (6 pts) Provide an acceptable name for each of the following molecules: 2-ethyl-1-pentene 3-vinylcyclopentanol trans-cycloheptene methylenecyclohexane 2,3-dimethylcyclopentene 5-bromo-6-methyl-5-hepten-3-ol 4. (5 pts) Provide the structural formula for each of the following molecules: I (Z)-3-methyl-2-octene vinylcyclopropane allyl iodide (Z)-2-bromo-2-pentene Trans-1,2-dibromoethylene

2 5. (5 pts) Assign E or Z configuration to each of the following compounds. D NT name the compounds! C 3 N C F C(C 3 ) 3 Z N E E 2 N Z Z 6. (3 pts) Indicate (Circle) the more stable species in each pair. Do not explain! or or 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; 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; (24 pts) Predict the principal organic product(s) in each of the following reactions. Draw the correct stereoisomeric product, wherever applicable.

3 P S 2 pyridine 2 light + RR 3 P C 4 NaC 2 C 3 C 3 C 2 1) B 3.TF 2) 2 2 / - MCPBA C 2 2 1) 3 2) (C 3 ) 2 S 9. Suggest an appropriate set of reagents/conditions and write an equation for each of the following transformations: A. (3 pts) Propane to 2-bromopropane; B. (3 pts) Cyclohexanol to cyclohexene; 2 light 2 S 4 C. (3 pts) 1-butanol to 1-bromobutane; P 3 D. (3 pts) 1-pentene to 1-pentanol; 1. B 3.TF / (4 pts) Acid-catalyzed dehydration of 2,2-dimethylcyclohexanol produces 1,2-dimethylcyclohexene as the major product. Write an equation and suggest a mechanism to explain this occurrence.

4 methyl shift 11. (4 pts) Suggest a DETAILED mechanism for the following reaction. + C C3 + C C C 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 2 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 2 5 C

5 C 3 C C 3 C 2 5 NaC 3 C 3 C 3 C 2 5 this hydrogen and chlorine are anti-coplanar and can be eliminated there are no β-hydrogens that are coplanar to chlorine. E2 elimination cannot occur 2 C 3 C 2 5 C 3 C (2 pts) Suggest the appropriate reagents/conditions in the following two-reaction sequence. 3 P 4 1) 3 2) 2, Zn (3 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-1,2- dibromocyclohexane, trans-2-bromocyclohexanol and trans-1-bromo -2-chlorocyclohexane. Suggest a detailed mechanism that accounts for the formation of ALL three products.

6 2 Na