Exam 2 FS10 - 1. (20 pts) (4 pts each) For each pair of...

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2 1. (20 pts) (4 pts each) For each pair of isomeric structures in the grid below, circle the more stable one, and provide a brief explanation. If you need more space, continue below (e.g. if you need to draw additional structures, etc.) Compounds Explanation OH O O O O H OH We saw that hydrogenation of a triple to a double bond is ca 10 kcal/mol more exothermic than double bond H2ation In 1,3-disubstituted cyclohexanes, the cis relationship keeps both groups equatorial. In general ! bonds are stronger the " bonds, and the 6-membered ring is no more strained than an open chain. O is much more electronegative than C, so putting (-) charge there, and spreading it out by resonance delocalization over two O's is by far better than putting it on C. Double bonds prefer more to be more substituted, so left structure with one tetrasubstituted double bond is better.
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3 2. (20 pts) Reaction of cis-2-butene with Br 2 as shown at right yields A and B : (a) (4 pts) Write the arrow-pushing mechanism for reaction of the alkene with Br 2 to form A and B . Be sure to make clear 3-D drawings. (b) (2 pts) Fill in the structure of B . (c) (2 pts) Name A , being sure to include stereochemical ( R & S ) configurations. Name: ( 2S,3S )-2,3-dibromobutane (d) (2 pts) On the template at right, make a Newman projection of compound A as seen by the eyeball shown above. (e) (2 pts) Besides A and B , there is a third stereoisomer of this formula, C , not formed by the above reaction . Draw it in the box using the same style as the original drawing above of A . (f) (3 pts) On the templates at right, draw Fischer projections of compounds A-C above. Label stereogenic C sites as R or S.
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Exam 2 FS10 - 1. (20 pts) (4 pts each) For each pair of...

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