Chapter 16, Problem 16.49SP

The proton NMR chemical shifts of the hydrogens in pyridine are shown. These are typical aromatic chemical shifts, except that the ortho protons (on the carbons bonded to nitrogen) are deshielded to δ8.60. A suitable oxidizing agent (such as a peroxyacid) can add an oxygen atom to pyndme to give pyridine N-oxide. The effect of this added oxygen atom is to shift the ortho protons upfield from δ8.60 to δ8.19. The meta protons are shifted downfield from δ7.25 to δ7.40. The para protons are shifted upheld, from δ7.64 to δ7.32. Explain this curious effect, shifting some protons upfield and others downfield.