CHEM210_Fall2008_Exam2_Answer_KEY - Name Page 1 I(26 points...

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Name _____________________ Page 1 I. (26 points) A. Vincamine is an alkaloid natural product that is used as a nootropic agent (a class of drugs that treat impaired cognitive abilities) to combat the effects of aging. It acts as a vasodilator, and increases blood flow to the brain. The structure of vincamine is provided below. (a) Circle all of the tetrahedral carbon stereocenters and clearly assign the stereochemical configuration for each stereocenter ( R or S ). N N H O O H 3 C OH Vincamine 9 S S S each stereocenter circled with correct R/S label = 3 each circle around an atom that is not a stereocenter = –1 (b) Check the boxes next to all (c) Draw the enantiomer of vincamine true statements about vincamine: Vincamine Is a chiral molecule. Has a chiral enantiomer. Has one meso stereoisomer. Has an achiral diastereomer. Has six chiral diastereomers. Is not optically active. 3 5 N N H O O H 3 C OH no partial X X X –2 for noncritical transcription error. Otherwise no partial. B. Using lines, dashes, and wedges to indicate stereochemistry when appropriate, draw the structure of ( E )-(2 S ,6 R )-6-bromo-5,5-diethyl-1-iodo-7-methyloct-3-en-2-ol. 9 I HO H H Br –2 for each error in stereochemistry, regiochemistry, or substituent type wedges/dashes on ethyl groups are optional
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Name _____________________ Page 2 O CH 3 O 2 N H 3 C H 3 CO OSi(CH 3 ) 3 A H H H H H 3 C K eq <1 =1 >1 K eq circle one answer in the box above 14 correct answer circled = 2 for each structure: correct connectivity = 2 THEN : chair shape including clear axial/equatorial bonds = 2 THEN : correct stereochemistry = 2 –2 once for incorrect enantiomer if consistent betwen both chair forms O O H OSi(CH 3 ) 3 H OCH 3 H NO 2 H 3 C CH 3 O 2 N H CH 3 OCH 3 H OSi(CH 3 ) 3 (b) How many signals (peaks) will appear in the 13 C NMR spectrum of A? 3 9 no partial B . For each of the pairs of molecules drawn below, place letters in the corner boxes corresponding to all accurate descriptions of the relationship between the two molecules. A enantiomers B diastereomers C different conformations of the same molecule D identical conformations of the same molecule E constitutional isomers F stereoisomers G different molecules H both are optically active I neither is optically active (a) H 3 C CH 3 HO Br H HO CH 3 Br CH 3 H
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  • Fall '08
  • Wolfe
  • H3C, Organic reaction, Electrophilic addition, Electrophilic aromatic substitution, aromatic substitution reaction

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