Question

Which one is the strongest acid Ortho or para nitrophenol

Answer 1

  p-nitrophenol is more acidic than o-nitrophenol, which is more acidic than m-nitrophenol. The o- and p- nitrophenolate conjugate bases are more stable than the m-nitrophenolate, because the negative charge can be delocalized onto the nitro group, which is not possible with the meta. The ortho nitrophenol is less acidic than the para, because the -OH group in the meta- compound can form a hydrogen bond to the adjacent nitro group, which stabilizes it (makes it harder for the H+ to leave).