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170 Organic Chemistry Solutions Manual Problem 6 In the chapter, we established that electron-withdrawing groups direct meta. Among such reactions is the nitration of trifluoromethyl benzene. Draw out the detailed mechanism for this reaction and also for a reaction that does not happen the nitration of the same compound in the para position. Draw all the delocalized structures of the intermediates and convince yourself that the intermediate for para substitution is destabilized by the CF₃ group while that for meta substitution is not. NO₂ NO₂ F₃C Purpose of the problem Making sure that you really do understand why groups like CF₃ are meta-directing. Suggested solution Just do what the question says! You need to do this once to convince yourself. In the mechanism for meta substitution, the positive charge in the intermediate is not delocalized to the carbon atom carrying the CF₃ group. + + NO₂ NO₂ NO₂ NO₂ NO₂ H H H In the mechanism for para substitution, the positive charge in the intermediate is delocalized to the carbon atom carrying the electron-withdrawing CF₃ group. This intermediate is unstable and is not formed. + H H H NO₂ NO₂ NO₂ NO₂ NO₂ + unstable Problem 7 Draw mechanisms for the following reactions and explain the position(s) of substitution. OH CI Br Br Br HNO₃ Br₂ CI AICI₃ NO₂ NO₂ Purpose of the problem Further exercises in explaining the position of substitution.