simple question (take two)

[MalibuPreMD]

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I asked this in the wrong forum and it was quickly locked. Apologies for that.

Anyway, simple question: I do not understand why carbonyl's are such strong bonds while simultaneously having a high potential energy. An example to illustrate my confusion. In orgo we learned that enol's quickly tautomerize to their carbonyl form. If you add their energies of dissociation, however, the carbonyl has a higher energy (not much, 50 kJ/mol I think), and is more EN (which also increases their energy). Furthermore, Oxygen is a smaller atom than carbon so there should be more energy derived from charge repulsion (more overlap of electric clouds). I know that c=o > c=c but I cannot rationalize why.

I thinks its the third day of school and I need something to stress out about... ugh.

 

[silverlion]

This is amazing! I was lying on my couch an hour ago contemplating the same question...but with lesser detail in head.

i was thinking of bond energies in general as well. There was a thread somewhere on examcrackers that addressed the question: Is an ionic bond stronger or is the covalent bond stronger. the answer was that objectively the ionic bond is stronger but then this question is rarely objective. Ionic and covalent bond strengths are always subjective and relative to a context that needs explanation.

My dreamy couch logic on the C=O vs C=C question was that while there is no electronegativity difference between the two carbons in a C=C bond there is hardly any ionic charecter in it...(If you would recall..books usually make it a point to mention the fact that no bond is completely covalent or completely ionic...) Now in the C=O bond the electronegativity difference causes an unsymmetrical charge distribution. This would introduce an electrostatic attractive force between the two atoms and therefore cause the bond to be shorter...thus stronger!!

Even though this makes some sense I am not quite convinced with the explanation myself...I would suggest something though ...Dont look too much into the electronic repulsion because of ths smaller size of oxygen....Simply look into electronegativities...I say this because when you go from basic knowledge to slightly higher level implications of the knowledge the whole point is to use the larger concepts...if you mix too many things into an explanation (like talking about electronegativities as well as the size of the atoms etc) then you are confusing yourself and making the logic a bit redundant...