Identification of an unknown surfactant

The large peak at 3.7 ppm corresponds to the ethoxylate protons ( c ). The small difference in chemical shift between c and d protons is due to a second-order effect both protons are deshielded by the electron-withdrawing inductive effect of an oxygen atom two bonds away, but the c protons feel the additional effect of the oxygen atom on the other side, i.e. three, bonds away, and therefore have higher chemical shift. 

Finally, the end cap methylene ( b ) resonates as a singlet at 3.9 ppm—further downfield of the ethoxylate protons because of the carbonyl carbon, which has an additional deshielding effect. Residual water in the solvent (D2O) can also be seen at 4.7 ppm. 

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