Q5 In the box below you are given the pKa values for a series of compounds the least acidic is cyclohexanol pKa 16 0 The pKa value for phenol is 10 0 and two series of substituted phenols are given 2 fluorophenol 3 fluorophenol and 4 fluorophenol have pKa values of 8 7 9 3 and 9 9 respectively 2 nitrophenol 3 nitrophenol and 4 nitrophenol have pKa values of 7 2 8 4 and 7 2 respectively Note both F and NO2 are strong electron withdrawing groups OH OH OH OH OH X X X pKa values cyclohexanol phenol 16 0 10 0 2 X phenol 3 X phenol 4 X phenol 8 7 9 3 9 9 X F 7 2 8 4 7 2 X NO2 a Briefly explain using words AND illustrations why phenol is literally and actually a million times more acidic than cyclohexanol 5 points 7 b Briefly explain using words and illustrations as you feel necessary the trend observed in the acidity of 2 3 and 4 fluorophenol 5 points c Briefly explain and illustrate why the trend observed in the acidity of 2 3 and 4 nitrophenol is different to that observed for the analogous series of phenolic compounds containing fluorine 5 points 8 EXTRA CREDIT The pKa values for 4 cyanophenol I and 4 nitrophenol II are approximately the same i e the phenolic protons bold in each of these compounds are equally acidic In contrast however the dimethyl substituted compounds differ significantly in their acidity the dimethyl cyano compound III is much more acidic than the dimethyl nitro compound IV Explain using both words and drawings as you feel appropriate this observation in the box below 15 points Hint think resonance OH OH OH OH vs vs Me Me Me Me CN NO2 CN NO2 I II III IV 7
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