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What are the resulting conjugate acid and base of phenol and 4-nitrophenol
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Irfan Aslam
What are the resulting conjugate acid and base of phenol and 4-nitrophenol
You can find the stronger acid by comparing the stability of their conjugate bases.
4-nitrophenol has the NO2 group (showing both electron withdrawing inductive and resonance effect) at the para position which will pull the electron pair away from the O- group. As you can see there is an additional resonance structure in its conjugate base giving it more stability.
Phenoxide ion shows one resonance form less making it less stable. Also it has no group which will inductively pull away the negative charge (which NO2 does very well), therefore we can conclude that 4-nitrophenol will in fact be the the stronger acid and protonate phenol.
You can find the stronger acid by comparing the stability of their conjugate bases.
4-nitrophenol has the NO2 group (showing both electron withdrawing inductive and resonance effect) at the para position which will pull the electron pair away from the O- group. As you can see there is an additional resonance structure in its conjugate base giving it more stability.
Phenoxide ion shows one resonance form less making it less stable. Also it has no group which will inductively pull away the negative charge (which NO2 does very well), therefore we can conclude that 4-nitrophenol will in fact be the the stronger acid and protonate phenol.
Unfortunately, this counting method, while it has been incredibly popular, is not based on any scientific rigor. You also only show the most prominent structures, but not all of them; the ionic ones are all missing. Nevertheless, while you can compare acidity based on $\mathrm{p}K_\mathrm{a}$ values, the remaining question is still: to what extent would/will a proton transfer happen. You also completely neglect whether or not the potonated forms will be stable enough to account for ionisation.More
You can find the stronger acid by comparing the stability of their conjugate bases.
4-nitrophenol has the NO2 group (showing both electron withdrawing inductive and resonance effect) at the para position which will pull the electron pair away from the O- group. As you can see there is an additional resonance structure in its conjugate base giving it more stability.
Phenoxide ion shows one resonance form less making it less stable. Also it has no group which will inductively pull away the negative charge (which NO2 does very well), therefore we can conclude that 4-nitrophenol will in fact be the the stronger acid and protonate phenol.
pKa(4-nitrophenol) = 7,15
pKa(phenol) = 9,95
You can find the stronger acid by comparing the stability of their conjugate bases.
4-nitrophenol has the NO2 group (showing both electron withdrawing inductive and resonance effect) at the para position which will pull the electron pair away from the O- group. As you can see there is an additional resonance structure in its conjugate base giving it more stability.
Phenoxide ion shows one resonance form less making it less stable. Also it has no group which will inductively pull away the negative charge (which NO2 does very well), therefore we can conclude that 4-nitrophenol will in fact be the the stronger acid and protonate phenol.
pKa(4-nitrophenol) = 7,15
pKa(phenol) = 9,95
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