Spectroscopic Features of Epoxides

IR Spectroscopy

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Epoxides, like ethers, generally have no easily distinguishable IR band but rather are identified based on:

• Knowledge that oxygen is present in the molecule;
• Absence of a C=O band (1650-1800 cm^-1)
• Absence of an O-H band (3200-3700 cm^-1

¹H NMR Spectroscopy

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As with ethers, there are signals for any proton on the oxygen-bearing carbon; however, the ring strain of the epoxide slightly changes the carbon hybridization and this the chemical shift. These now will occur further upfield, between 2-3.5 ppm and will couple normally to any neighbors. (the electron-withdrawing nature of the aromatic ring deshields the benzylic proton in the epoxide.)

¹³C NMR Spectroscopy

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Likewise, epoxides contain carbons bearing an oxygen which are deshielded, but occur a bit upfield of an ether, normally occur in the 30-60 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.