4
$\begingroup$

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?

$\endgroup$
4
  • 2
    $\begingroup$ 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
6
$\begingroup$

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.

Reference

  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)
$\endgroup$
0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.