The Characteristic Values of Chemical Shifts

Approximate values of chemical shifts for different kinds of protons are listed in Table 15.1. (A more extensive compilation can be found in the Study Guide and 

In a similar environment, the signal for a methine proton occurs at a higher frequency than the signal for methylene protons, which occurs In turn at a higher frequency than the signal for methyl protons. 

An H NMR spectrum can be divided into seven regions, one of which is empty. If you can remember the kinds of protons that appear in each region, you will be able to tell what kinds of protons a molecule has from a quick look at its NMR spectrum. 

The signal for the a protons of 2-methoxypropane is the one at the lowest frequency because these protons are farthest from the electron-withdrawing oxygen. The b and c protons are the same distance from the oxygen, but the signal for the c protons appears at a higher frequency because, in a similar environment, a methine proton appears at a higher frequency than do methyl protons. 

Which of the underlined protons (or sets of protons) has the greater chemical shift (that is, the higher frequency signal)  

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