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If $\ce{C2O4}$ is very unstable no matter the configuration(that is the structure based on the bonds) and especially unstable in the form that has an oxyanion and a carbocation than how come other carbon oxides are much more stable despite the charges like $\ce{CO}$ for instance.

There are 2 possible structures with octets for this. They are

1) $\ce{C=O}$ with the carbon having 1 lone pair and the oxygen having 2 lone pairs. No charges here.

2) $\ce{C≡O}$ with $\ce{C}$ having 1 lone pair and $\ce{O}$ having 1 lone pair making the oxygen positive and the carbon negative.

This one is an important but very unstable structure.

Why is it so unstable? It is because while carbon isn't so determining as to what charge it prefers, Oxygen is and it really hates being positive because it wants to be either neutral or negative since it is more electronegative than everything else except fluorine. This is why $\ce{H3O+}$ isn't really $\ce{H3O+}$ but rather an ion in a complex of ions is because of how oxygen hates being positive.

So why are other carbon oxides more stable than $\ce{C2O4}$ when they too have very unstable structures like $\ce{CO2}$ having as a resonance structure a single bond to 1 oxygen making it negative, a triple bond to the other making it positive, and the carbon staying neutral? And if every carbon oxide is either unstable no matter the structure or has unstable resonance structures than why do carbon oxides with just carbon and oxygen exist?

And would adding hydrogens to a carbon oxide make the carbon oxide even more stable? By this I mean that with the fact that carbon oxides tend to be unstable and hydrocarbons tend to be stable would a carbon oxide with hydrogens added to it be less stable than a hydrocarbon but more stable than a carbon oxide?

Is this how come glucose is so stable and 6 $\ce{CO}$s bonded together would be extremely unstable just like $\ce{C2O4}$ is?

Sorry if it is too many questions but it is all about 1 thing, Carbon Oxides.

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  • $\begingroup$ On the bonding in $\ce{CO2}$ is partly an answer by me here: chemistry.stackexchange.com/q/10976/4945 $\endgroup$
    – Martin - マーチン ♦
    Jul 31, 2014 at 15:13
  • $\begingroup$ thats just about the standard 2 C=O bonds. CO2 also has an unstable resonance structure like this: O-C-=O(-= means triple bond). 1 oxygen being positive and the other being negative with the carbon staying neutral is unstable. It is sort of like how in CO the triple bond resonance structure is unstable because of how the carbon is negative and the oxygen is positive. $\endgroup$
    – Caters
    Jul 31, 2014 at 15:15
  • $\begingroup$ First thing you need to understand is, that the real bonding situation lies between all possible resonance structures. A resonance structure is only a concept, so that the human brain can begin to understand the bonding in such molecules. These structures do in no way represent any physically observable quantity. The bonding especially in these very small molecules is very complicated and complex and hard to comprehend. That's why we need simpler models to explain them. Btw, do you mean $\ce{^{\ominus}O-C#O^{\oplus}}$? $\endgroup$
    – Martin - マーチン ♦
    Jul 31, 2014 at 15:24
  • $\begingroup$ yes that is what I mean for the unstable resonance structure of CO2. $\endgroup$
    – Caters
    Jul 31, 2014 at 15:30
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    $\begingroup$ There are plenty of other carbon oxides - for example mellitic anhydride and graphite oxide have been known since the 1800s. $\endgroup$
    – Ben Norris
    Aug 1, 2014 at 1:38

1 Answer 1

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Why is $\ce{C2O4}$ unstable?

Have you tried drawing it?

I get four different kinds of structures for it:

  1. $\ce{(O=)O^{.}C-CO^{.}(=O)}$
  2. $\ce{(O^{.})2C-C(O^{.})2}$
  3. $\ce{O#C-O-CO^{.}(=O)}$
  4. $\ce{O#C-O-O-C#O}$

They are unstable for the following reasons:

  1. Biradical
  2. Tetraradical (This won't really exist anywhere near anything else.)
  3. Radical
  4. Peroxo bond, very easy to break homolytically.

All of these compounds can easily decompose to give (the thermodynamical Mariana trench) carbon dioxide: $$\ce{C2O4 -> 2CO2}$$

That is why it is so unstable.

Reduce 'em!

And would adding hydrogens to a carbon oxide make the carbon oxide even more stable?

Yes. If you start reducing the compounds above, you will end up with ketones and water (because geminal hydroxy groups tend to give water and ketones), or even alcohols (if you continue reducing).

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