| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 5229432 | Tetrahedron | 2007 | 7 Pages |
Multinuclear magnetic resonance and IR spectra prove that although 2-(diacylmethyl)pyridines and 2-(diacylmethyl)quinolines are β-diketones, their proton transfer product present in chloroform solution is not ketoenol but enaminone (earlier opinions were contradictory). Quinoline derivatives are less zwitterionic by character than the respective pyridyl congeners. The β-diketone form itself may also be rarely present in the solution. X-ray data show that 2-(2(1H)-pyridinylidene)-1H-indene-1,3(2H)-dione, i.e., enaminone tautomer of 2-(pyridin-2-yl)-2H-indene-1,3-dione, is also the only form present in crystal. Ab initio calculations show that the enaminone is usually more stable than other tautomeric forms. Values of geometry based aromaticity index HOMA (harmonic oscillator model of aromaticity) confirm that the zwitterionic structure really contributes to the enaminone forms detected.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide
