11.* (1995 1 3) Consider a hydrocarbon, X (molecular formula C5H8) which is optically active. This substance manifests all three hybridization states of carbon (sp, sp2, and sp3). Reaction of X with H2 over Pd metal catalyst forms n-pentane. Such reactions do not break carbon-carbon bonds. A. How many sites of unsaturation are in X? B. Draw three dimensional structural formulas for X and for any stereoisomers of X. Can you distinguish between the stereoisomers using the information given here? C. Are there any chiral carbon centers in X? D. Indicate the hybridization states of each carbon in X by drawing an arrow from the symbols, sp, sp2, and sp3 to these carbon atoms.
12.* (1994 1 3) Below are two structures (X and Y) for 2,3-difluorobutane. The first structure is shown in Newman projection; the second is a "sawhorse" representation. True or false?
A. X and Y are identical representations of a single stereoisomer. B. X is optically active. C. Y is optically active. D. X and Y have different boiling points. E. The conformations represented by X and Y are eclipsed. F. The proper name for Y would be R,S (or S,R).
13.* (1994 1 5) The reactive compound 1,4-dibromobuta-1,2,3-triene has the molecular formula C4H2Br2. Show line-bond structures, hybridization state of each carbon, shape of molecule, and any stereoisomers and whether they are chiral.
14.* (1994 1 6) Two structures for thalidmoide are shown below.
A. Which of the following terms describe these substances: B. Designate each of these compounds as R or S. C. How many sites of unsaturation are found in thalidomide? Identify these. D. Are there any aromatic groups in thalidomide? Explain.
15.* (1993 1 4C) Which substances would you rather try to resolve into optical isomers (enantiomers)? Expain. (R,S)-2,3-diaminobutane and (S,R)-2,3-diaminobutane or (S,S)-3,4-diaminohexane and (R,R)-3,4-diaminohexane
16.* (1990 F 8) A student wanted to resolve 2R, 3S-butane-2,3-diol. What advice would you offer this student in carrying out this experiment?
17.* (1990 F 9) E-b-farnesene, the aphid alarm pheromone, is produced in the leaves of the Bolivian potato which is not attacked by aphids.
A. Is it chiral? B. Exhaustive hydrogenation saturates all of th olefinic bonds but no skeletal rearrangement occurs. Write structural formulas for the products of hydrogenation and comment on optical activity. C. Is there any conjugation in this molecule? D. Where does the "E" come from?
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