Week_5.2_PurpleBook_Answers

Week_5.2_PurpleBook_Answers - 123 More Anomeric Effect Week...

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b) The two conformers of the nitrite ester shown below have slightly different bond lengths (as indicated). (Note that both conformations are entirely planar. How are the bond lengths different between A and B ?) NO O H 1.19 Å 1.39 Å There is an important orbital interaction in conformation B which is not present in conformation A : Olp donating into σ * N–O 1. Each of the following observations can be explained by a frontier molecular orbital ( FMO ) argument. Provide such an explanation for each observation. Be sure to label the relevant donor-acceptor interactions and provide a clear diagram showing the interacting orbitals. (An energy-level diagram is not expected.) 1.17 Å In conformation A the orbitals are not aligned properly for this lone pair -> σ * donation. which makes the N=O bond longer and the central N–O bond shorter NO O R NO O R More Anomeric Effect 1.43 Å B A H 3 C O CH 3 O H 3 C O O CH 3 a) The following ester prefers conformation A rather than conformation B .( Hint :Cons ider all the lone pairs in the molecule. A "steric" argument is not acceptable.)
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This note was uploaded on 05/01/2008 for the course CHEM 51 taught by Professor Gribble during the Spring '08 term at Dartmouth.

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Week_5.2_PurpleBook_Answers - 123 More Anomeric Effect Week...

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