14C_f09_finalB_key

14C_f09_finalB_key - Chemistry 14C Fall 2009 Final Exam...

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Chemistry 14C Fall 2009 Final Exam Part B Solutions Page 1 Statistics : High score, average and low score will be posted on the course web site after exam grading is complete. The exam is ready to be picked up when these numbers are posted. A note about exam keys : The answers presented here may be significantly longer than expected from a student taking the exam. An exam key serves not only to reveal what was expected, but to instruct you as well. To see the projected course grade cutoffs, consult the grading scale on the Chem 14C course web page. The final grade cutoffs cannot be determined until after the final exam has been graded. 1. N F N NH O O HO N F N NH O O HO 2. Influence #1 : Resonance causes some or the entire molecule to be planar. Influence #2 : Resonance increases stability. Influence #3 : Resonance causes electron delocalization. 3. Coplanar The carboxylic acid and ring B have this geometry because it allows for conjugation between the C=O and the B ring aromatic electron cloud. 4. N F N N O O O H H 5. Ten 6. A, B, and C 7. Of the carbon stereocenters in penicillin G, two have the R configuration, one has the S configuration, and zero are not R or S . Not including the structure shown above, there are 2 3 - 1 = 7 penicllin G stereoisomers. 8. Several answers are possible. Invert at least one, but not all, of the stereocenters of penicillin G. For example invert only the stereocenter bearing the carboxylic acid: N S CH 3 CH 3 COOH N O H O 9. (d) No conclusions can be drawn concerning the drug properties of the enantiomer.
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Chemistry 14C Fall 2009 Final Exam Part B Solutions Page 2 10. The carboxylic acid of penicillin G is a stronger acid than acetic acid because the electron-withdrawing inductive effect of the nearby nitrogen atom stabilizes the penicillin carboxylate (the conjugate base of the
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This note was uploaded on 08/02/2011 for the course CHEM 14C taught by Professor Hardinger during the Fall '08 term at UCLA.

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14C_f09_finalB_key - Chemistry 14C Fall 2009 Final Exam...

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