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Which of the underlined protons in each pair absorbs farther downfield in NMR spectrum #CH_3CH_2CH_3# or #CH_3OCH_3#?

Answer 1

The #"CH"_3# protons in #"CH"_3"OCH"_3# absorbs further downfield.

The #"CH"_3# group in #"CH"_3"OCH"_3# is deshielded by the electronegative #"O"# atom.

Downfield absorption is shifted by deshielding.

Therefore, we anticipate that compared to methyl protons in propane, methyl protons in dimethyl ether should absorb farther downfield.

Their NMR spectra support this prediction.

Propane's methyl groups have a chemical shift of δ = 0.9, whereas dimethyl ether has a chemical shift of δ = 3.2.

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Answer 2

Ellie Adams

The underlined proton in CH₃OCH₃ absorbs farther downfield in the NMR spectrum.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.