For example, the protons of a methyl group which is bonded to a saturated carbon atom absorb at δ=0.67 - 1.83 ppm, those3 of a methyl group bonded to nitrogen absorb at δ =2.16 - 3. 33ppmand those of a methyl group bonded to oxygen absorb at δ = 3.33 - 4.00 ppm.