The Mills-Nixon effect on enol-enol tautomerism in β-dicarbonyl compounds and on annular tautomerism in NH-pyrazoles: A semi-empirical study

✍ Scribed by Mar Ramos; Ibon Alkorta; José Elguero

• Book ID: 104207429
• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 306 KB
• Volume: 53
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(96)01052-6

✦ Synopsis

AMI semiempirical calculations, both AH and AS, were carried out on the enol/enol tautomerism of 2513-diketones and 813-ketoaldehydes. In the first case, q~AGex p was determined by Hansen (Magn. Reson. Chem. 1996, 34,467) and his values correlate reasonably well with 8AGcalc, 8AGexp = -0.23 + 0.29 8AGealc, r 2 --0.83. The calculated differences in energy are linearly related to some geometrical characteristics of the ketoenoi, namely the angles about the substituent on the central carbon.

To check if this geometrical dependence is related to the Mills-Nixon effect, parallel AM1 calculations on the tautomerism of ~-ketoaldehydes and 3(5)A-disubstituled NH-pyrazoles were carried out confirming the influence of the Mills-Nixon effect on the enol/enol tautomerism of ~-dicarbonyl compounds.