Explain why diethyl ether does not have a UV spectrum, even though it has lone-pair electrons.

Can we say that π* molecular orbital does not exist because there are no π-bonded electrons in diethyl ether?

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    $\begingroup$ Its uv spectrum is most likely due to non bonding lone pair to $\sigma^*$ or $sigma\to \sigma^*$ orbitals which may be too far into the uv (<215 nm for ether) to be measured properly on a typical spectrophotometer. $\endgroup$ – porphyrin Nov 27 '20 at 8:50
  • $\begingroup$ @porphyrin Ad hoc find on pages 61 and 62 of this presentation for cooled solid forms of diethyl ether: home.strw.leidenuniv.nl/~ewine/photo/workshops/2015-02/… $\endgroup$ – Buttonwood Nov 27 '20 at 11:51
  • $\begingroup$ @Buttonwood, this should have been a v. interesting talk. The effects of the solid state vs. gas phase are understandable in general terms but being specific for any individual case must be hard. $\endgroup$ – porphyrin Nov 27 '20 at 19:33
  • $\begingroup$ @porphyrin The setup of the substrate (close to Knudsen cell like deposit of a substrate on a sample holder cooled well below the melting point of substrate) and subsequent (cycles of) annealing by controlled heating reminded me on impedance / broadband dielectric spectroscopy in soft matter research about relaxation processes in solid matter / supercooled liquids. Maybe the VUV spectroscopists deposit on comb electrodes anyway to record complementary data on the other side of the electromagnetic spectrum, too ... $\endgroup$ – Buttonwood Nov 28 '20 at 10:56

We can measure the UV-Vis spectra for π → π* or n → π* electronic transitions (other transitions are forbidden according to selection rule) [1, pp. 577–578]. But in diethyl ether, being a saturated compound, it has no π-bonds. This successfully dismisses the idea of having π* orbital. And, as there is no π* orbital, we can not have a transition to the π* orbital resulting in no UV-Vis absorption spectra.


  1. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Vyvyan, J. R. Introduction to Spectroscopy, 5th ed.; Cengage Learning: Stamford, CT, 2015. ISBN 978-1-285-46012-3. (PDF)

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