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My textbook (NCERT Chemistry. Part I. Textbook for Class XI [1, p. 106]) states that

Resonance stabilizes the molecule as the energy of the resonance hybrid is less than the energy of any single canonical structure

by giving two examples: $\ce{O3}$ and $\ce{CO2}.$

While I can see that clearly in case of $\ce{O3}$ molecule, I can't see that how resonance lead to lowering of energy as in case of $\ce{CO2}$ as two of its canonical structures have formal charge separation, while the one without formal charge separation seems to be more stable than the other two and hence the overall resonance hybrid.

It looks to me that the structure of $\ce{CO2}$ without formal charge separation is the correct one but spectroscopic data suggests that it has to be a resonance hybrid.

What am I missing?

References

  1. Ashok Srivastava; Kalyan Banerjee; Gautam Ganguly; Naresh Yadav; Mathew John; Rajender Chauhan. Chemistry. Part I. Textbook for Class XI; NCERT: New Delhi, 2006. ISBN 81-7450-494-X.
andselisk
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Aditya
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    What the book means is probably that the actual structure of CO2 has a bond length shorter than that of a "typical" C=O bond (in carbonyls, around 123 pm; in CO2, 116 pm; in CO, in which a pure triple bond is present, 113 pm), so it has a partial triple bond character, as the canonical forms with charge separation suggest –  Dec 29 '19 at 13:49
  • @The_Vinz I like your about me column :) – Zenix Dec 29 '19 at 14:53

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