4
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My reasoning for the somewhat implausible "$\mathrm{sp^2}$" character of the hydrogen between these two oxygens on the enol structure of the right comes from recognizing that if it were, then we would have 6 $\mathrm{sp^2}$ atoms with 6 π-electrons, so maybe that extra bit of instability from having a higher orbital on hydrogen could be sort of taken care of by being stable like an aromatic compound and forming a hydrogen bond.

So how could I go about figuring out if this is true, either with MO theory or something else?

dicarbonyl

(source: ucdavis.edu)

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  • $\begingroup$ So are you asking whether the hydrogen $2p$ orbitals are involved in bonding? $\endgroup$ – bon Sep 3 '15 at 16:41
  • $\begingroup$ Yes, I think so, or if they are occupied ever, for instance would I expect this compound to experience a chemical shift when put into a magnetic field similar to an aromatic compound. $\endgroup$ – user19026 Sep 3 '15 at 16:46
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    $\begingroup$ Not a chance. 2p are just too far away. Look at the energy levels diagram. $\endgroup$ – Ivan Neretin Sep 3 '15 at 16:52
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    $\begingroup$ Wait a minute. Diborane is electron-deficient, but this thing is not. See, we had a normal 2-electron O-H bond, then another O went in with its lone pair (2 more electrons). If anything, this should be a 3-center-4-electron construction. $\endgroup$ – Ivan Neretin Sep 3 '15 at 17:17
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    $\begingroup$ @IvanNeretin Yes, I agree, I should have written "3-center-4-electron" in my earlier comment. Thanks for catching that. $\endgroup$ – ron Sep 3 '15 at 20:19

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