Sketch the Lewis structure of all trans-2,4,6-octatrienoic acid.

(a) Consider the delocalized π electrons. Employ the particle-in-a-box model. Drawing on your knowledge about the occupation of orbitals in atoms what is the highest occupied state? Sketch the occupation of the energy levels with electrons using ↑ and ↓.

I wondered if the electron lone pairs on the oxygen atoms also counted as π electrons since resonance structures exist where these lone pairs can be delocalised over the molecule.

all trans-2,4,6-octatrienoic acid

If so, how would this correspond to using them to find the length of the conjugated system because wouldn’t that give extra length where there was no double bond?

  • 1
    $\begingroup$ No, discard them. Also, are you sure that such resonance structures exist? $\endgroup$ Mar 2 at 21:48
  • $\begingroup$ Which oxygen do you mean? The carbonyl oxygen (=O) lone pairs are orthogonal and cannot participate in the resonance. The carboxyl oxygen (-OH) can participate in resonance to some extent, but since the question asks about particle in a box model, you can't really consider that. $\endgroup$
    – S R Maiti
    Apr 3 at 21:49
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    $\begingroup$ In UV-Vis spectroscopy, these two electron pairs on carbonyl-O and alcohol-O are named n electron pairs because these are not shared with the extended $\pi$ electron system. $\endgroup$
    – Buttonwood
    May 29 at 18:06

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