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I'm virtually all chemistry books I own say that benzene is more stable than the theoretical cyclohexatriene, by 150 kJ to be specific, due to the delocalization of pi electron density around the ring.

I've come across many explanations for this such as "spreading of charge minimizes repulsion" and "particle-in-a-box from quantum mechanics", but these explanations don't really seem satisfactory. If delocalization or spreading of charge does is in fact stabilizing, why doesn't it occur in every molecule? (I am aware that electrons are actually delocalized in every molecule but I'm referring to the uniform spread of charge that occurs in benzene.)

I feel that the statement that "delocalisation stabilises benzene" is misleading at the very least. The actual electronic distribution of any molecule is, by definition, the one with the lowest possible energy. So any inaccurate lewis structure must have a higher energy than the actual one. So shouldn't the correct statement be "benzene is more thermodynamically stable than cyclohexatriene because the actual benzene has delocalised π electrons while cyclohexatriene does not, so cyclohexatriene is an inaccurate and thus less stable electronic configuration"?

I've asked this question from my teacher but he says he's never heard of this.

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  • $\begingroup$ Not all molecules have proper conjugated pi bond system. $\endgroup$
    – Poutnik
    Sep 18 at 5:37
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    $\begingroup$ What you say of the lowest possible energy is correct. But I think the statement in question is less misleading than you feel. This is where it really leads: "Delocalisation stabilises benzene as compared to the theoretical cyclohexatriene, thus making the latter structure impossible, or in other words, inaccurate". How about that? $\endgroup$ Sep 18 at 8:45
  • $\begingroup$ I think my main issue is the implication that delocalization of charge is somehow a universal stabilizing factor, stemming from statements like "benzene is stabilized due to delocalization" that do not mention that this "stability" is only relative to an inaccurate description $\endgroup$ Sep 18 at 9:15
  • $\begingroup$ Yes. Common statements often have implicit parts. See Ivan Neretin. But the distilled juice is already in your question. So you are (were) over thinking. And yes delocalisation always take place, just not the one intended, that as per the Poutnik comment, needs structural requisites. $\endgroup$
    – Alchimista
    Sep 18 at 9:42
  • $\begingroup$ As you suspect, delocalisation isn't always more stable: see cyclobutadiene (4 pi electrons). $\endgroup$
    – orthocresol
    Sep 18 at 16:49

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