# Does alcohol hydrogen in the enol tautomer of a β-dicarbonyl have sp² character?

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?

(source: ucdavis.edu)

• So are you asking whether the hydrogen $2p$ orbitals are involved in bonding? – bon Sep 3 '15 at 16:41
• 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. – user19026 Sep 3 '15 at 16:46
• Not a chance. 2p are just too far away. Look at the energy levels diagram. – Ivan Neretin Sep 3 '15 at 16:52
• 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. – Ivan Neretin Sep 3 '15 at 17:17
• @IvanNeretin Yes, I agree, I should have written "3-center-4-electron" in my earlier comment. Thanks for catching that. – ron Sep 3 '15 at 20:19