Spectroscopic Features of Ethers

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IR Spectroscopy

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Ethers and epoxides generally have no easily distinguishable IR band but rather are identified based on:

There are actually assignable C-O bands between 1300-1000 cm-1 in this molecule. Because there are often overlapping fingerprint-type bands nearby, assignment can be impossible without comparing the isotopically labeled (18O) compound.

1H NMR Spectroscopy

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As with alcohols, there is a signal for any proton on the oxygen-bearing carbon; this will occur between 3.3-4.5 ppm and will couple normally to its neighbors. Note that MTBE has two oxygen-bearing carbons; one has hydrogens (and shows the highlighted signal); the other has NO hydrogens but only methyl substituents (which appear normally, upfield).

Again, click on any signal to highlight the proton responsible for it.

13C NMR Spectroscopy

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Like alcohols, ethers contain carbons bearing an oxygen which are deshielded and normally occur in the 50-80 ppm region; a carbon with more than one oxygen may be further downfield. Epoxide carbons come at higher field (45-55 ppm) because of the effects of ring strain, as is seen in the 1H NMR.

Mass Spectroscopy

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The radical cation of MTBE is so unstable we do not see a parent ion (m/z = 88). Instead, "α-cleavage" leads to loss of a methyl group and a peak at m/z = 73.

Look at spectra of epoxides