CHEM 239 exam_answers_Exam_3_key

CHEM 239 exam_answers_Exam_3_key - W £1 ? WET} if?...

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Unformatted text preview: W £1 ? WET} if? Chemistry 239 Autumn, 2007 Exam 3 Answer Key Your name: Student #: Sign here to indicate your approval of public return of your paper: 1 (24 pts.) Give structures or names for the compounds below. Ho OH H H H H H H CHZOH Z'naphthOI D-galactitol D-gluconic acid Fischer projection Fischer projection 2,3,4-tri-O-methyI-D-allose H HHJH \ / \ , / CZC ~ C17C / I \CHZ/ \(CH2)7C02H CH3(CH2)12C02H CH3(C3Hz)4 steroid ring system 2 (6 pts.) Complete a balanced equation for a proton transfer between the reactants below, label the stronger and weaker acids involved, and indicate whether the position of equilibrium is favorable (to the right) or unfavorable (to the left). MeNH3+ + on—Q—O' 2:2. MeNHZ + OzN—Q—OH weaker acid linoleic acid show stereochemistry I stronger acid 4—— [PKA "' 10] unfavorable [pKA < 10] ;. Chem 239 Autumn, 2007 Exam 3 Answer Key p. 2 3 (24 pts.) In the reactions below fill in the missing items (starting material[s], reagents and conditions over the arrow, or main organic product[s]). COZ A H30+ ———> Me H —> Me O H heat pressure COZH CHO ,cozH ' l:l-l-—+—OH:|‘1 [HiOHJ4 CHZOH' COZH show chair for cyclic hemiacetal with stereochem also 440ch , n _/'\g 4 (8 pts.) Draw the structure of the alditol that would‘th formed/from D—lyxose below. Indicate whether the alditol would be opticallv‘a'ctive or not. Can you draw the structure of a different aldose that would give the same alditol as that from D—lyxose (explain)? V Ho CHZOH H H H the aldose to the right H H H I H (which is D-arabinose) ’ H V H would also give the H20“ I “20” same alditol optically active Chem 239 Autumn, 2007 Exam 3 Answer Key p. 3 ————.—____....___..___..________________ 5 (12 pts.) A branched polysaccharide is hydrolyzed by a—glycosidase enzymes but not by ‘ B~glycosidase enzymes. Methylation followed by hydrolysis gives mainly—2,3,4- tri—O—methyl-D—mannose, along with a small amount of 2,3-di-O-methyl—D- \ mannose. Sketch the structure (showing all rings as‘chairS) of the branching point of the polysaccharide, as well as the repeating chain structures leading away from the branch point. 6 (6 pts.) Classify the terpene vitamin A (below) according to type of terpene (e.g., monoterpene, etc.) and outline how isoprene skeletons might form the structure. diterpene [,Czo] Chem 239 Autumn, 2007 Exam 3 Answer Key p. 4 7 (10 pts.) Show curved arrows for all steps in the mechanism to form the diene (below left) from the pyrophosphate (below right) shown. 8 (10 pts.) A naturally occuring monoterpene hydrocarbon reacts with 2 mol equivalents of hydrogen upon catalytic hydrogenation to give 1-methy1—4- isopropylcyclohexane. Ozonolysis of the monoterpene gives the products shown below (1 mol equiv. each). Propose a structure for the monoterpene . and show shorthand equations for both reactions. 1, 03 2. Zn, H+ H2, Cat- CIZHO + ‘ ...
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CHEM 239 exam_answers_Exam_3_key - W £1 ? WET} if?...

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