817. (4 pts) Select the reagent and solvent combination which would result in the fastestrate of substitution (R = CH3in all cases). I25oC?a)ROH, HMPA b) RS–, H2O c) RO–, H2O d) RS–, DMSO e) RSH, H2O Comments: SN2 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 conformationof (1R)(2S)-1,2-dichloro-1-methylcyclohexane? ClCH3HHClCH3ClH3CClCla)b)c)d)HClHHClCH3HHClHHHClHH3CCle)HHHHHHFischer projectionHHComments: 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
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