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Final - Fall 200609 - d There is only 1,2-adduct possible...

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9 20 . (4 pts) What is the major organic product of the reaction shown below? 1. MCPBA 2) HBr, Et 2 O ? Br Br OH OH Br O e) a) b) c) d) OH OH Comments: This question tests for understanding of acid-catalyzed reactions of epoxides. The epoxide formed with MCPBA is protonated and opened with Br acting as the nucleophile. As discussed in class the behavior is analogous to that observed for bromonium ions, i.e. Markovnikov’s regiochemistry. Similar problems include: TS4: 73, or book p. 651. 21-22 . In general, different isotopes of the same atom have almost indistinguishable reactivities. Consider the reaction of 1 equivalent of D-Cl with 1,3-cyclopentadiene where D = 2 H. D-Cl 21 . (2 pts) Which is true about this reaction? a) The 1,2-adduct is the kinetic product, and the 1,4-adduct is the thermodynamic product. b) The 1,4-adduct is the kinetic product, and the 1,2-adduct is the thermodynamic product. c) The kinetic and thermodynamic products are the same, except for isotopic substitution.
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Unformatted text preview: d) There is only 1,2-adduct possible in this reaction. e) There is only 1,4-adduct possible in this reaction. 22. (2 pts) How many isomers, including stereoisomers, form in this reaction? a) 2 b) 4 c) 6 d) 8 e) 16 D-Cl D D Cl Cl D D Cl Cl 1,2-1,4-Comments: This question is about conjugate addition. A simple drawing of the two resonance structures of the allylic cation is all that is needed to draw the products. As can be seen the 1,2- and 1,4- adducts are the same, except for the isotopic substitution. Since the deuteration (addition of D + ) can happen from either face of the ring, and the addition of Cl – to the planar carbocation can also happen from both faces, all stereochemical outcomes are possible on both chiral centers in each adduct, giving 8 total isomers. Similar problems include: PE4A: 8 and homework 14.26. Counting isomers (including stereoisomers) is standard on our exam)....
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