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Unformatted text preview: 8 17. (4 pts) Select the reagent and solvent combination which would result in the fastest rate of substitution (R = CH 3 in all cases). I 25 o C ? a) ROH, HMPA b) RS , H 2 O c) RO , H 2 O d) RS , DMSO e) RSH, H 2 O Comments: S N 2 reactivity patterns are tested here. The difference is to select the best nucleophile (charged and polarizable) and the best solvent (polar aprotic). There are several examples of this type of questions in the practice set: TS4: 58, 59-62, PE4A: 22-25. 18 . (4 pts) What is the best representation of the lowest energy conformation of (1 R )(2 S )-1,2- dichloro-1-methylcyclohexane? Cl CH 3 H H Cl CH 3 Cl H 3 C Cl Cl a) b) c) d) H Cl H H Cl CH 3 H H Cl H H H Cl H H 3 C Cl e) H H H H H H Fischer projection H H Comments: This is another version of the question that was on every exam in the practice set concerning representation of stereochemistry (including your exam 2). The best way to approach the problem is to build a model (or assign absolute configurations to the drawings). The only consideration is that in the build a model (or assign absolute configurations to the drawings)....
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- Fall '07