Final - Fall 200602

Final - Fall 200602 - reaction of the epoxide shown below?...

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2 3. (4 pts) In the reaction shown below, the carbon marked by a dot (•) is 13 C isotope that can be distinguished from “normal” carbons ( 12 C) by a special kind of spectroscopy. H 2 SO 4 Which structure shows the correct position of 13 C in the product of the carbocation rearrangement shown above? a) b) c) d) e) Comments: This question is an example of a carbocation rearrangement. An almost identical case was discussed in detail in class (check October 20 News), and numerous similar examples were in practice set (see for example TS4: 28, PE4B: 4, Book: 6.49). A simple pencil-and-eraser technique is enough to answer this question. 4. (4 pts) What is the crucial intermediate with the correct mechanistic arrows for the ring-opening
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Unformatted text preview: reaction of the epoxide shown below? O ? 2. H 3 O + Product 1. CH 3 MgBr O H + O O O a) b) c) d) H 3 C MgBr H 3 C MgBr H 3 C MgBr H 3 C MgBr Comments: This is an example of nucleophilic ring opening of epoxides. It was sufficient to recognize that this is an S N 2 reaction, with the release of ring strain, providing the driving force. S N 2 reactions take place on the back-side of the leaving group ( σ * C-O bond is the LUMO) and on the less sterically crowded carbon. Grignards as strong bases cannot coexist with acids (excluding (a) as an option). Similar example was in TS4: 74....
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This note was uploaded on 01/12/2010 for the course PSYCH 100 taught by Professor Matchock,robert during the Fall '07 term at Penn State.

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