Which of the underlined protons in each pair absorbs farther downfield in NMR spectrum $C H_{3} C H_{2} C H_{3}$ $CH_3CH_2CH_3$ or $C H_{3} O C H_{3}$ $CH_3OCH_3$ ?

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Answer 1 · 2015-07-31T14:23:25

The ${CH}_{3}$ $"CH"_3$ protons in ${CH}_{3} {OCH}_{3}$ $"CH"_3"OCH"_3$ absorbs further downfield.

The ${CH}_{3}$ $"CH"_3$ group in ${CH}_{3} {OCH}_{3}$ $"CH"_3"OCH"_3$ is deshielded by the electronegative $O$ $"O"$ atom.

Deshielding shifts the absorption downfield.

So we predict that the methyl protons in dimethyl ether should absorb further downfield than the methyl protons in propane.

This prediction is confirmed by their NMR spectra.

The chemical shift of the methyl groups in propane is δ = 0.9, while for dimethyl ether the chemical shift is δ = 3.2.

Which of the underlined protons in each pair absorbs farther downfield in NMR spectrum CH3CH2CH3CH_3CH_2CH_3 or CH3OCH3CH_3OCH_3?