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Type: Artigo de periódico
Title: Keto-enol Tautomerism Of Some Ortho-substituted α-methylthio-α- Diethoxyphosphorylacetophenones
Author: Olivato P.R.
Rodrigues A.
Rittner R.
Abstract: The existence of the keto-enol equilibrium in diluted solutions of ortho-substituted α-methylthio-α-diethoxyphosphorylacetophenones X-PhC(O)CH[SMe][P(O)(OEt)2] (X=OMe 1, Me 2, F 3, Cl 4 and Br 5) has been detected through IR (νOH, νCO and νP=O) and NMR (1H, 13C and 31P) analyses. The enol form exists as a strong intramolecular hydrogen bonded 'conjugated chelate'. For compounds 1 and 3 for which the ortho-OMe and F substituents are almost coplanar with respect to the C=O group, their strong +M effect gives rise to a strong πX-πPhC(O) conjugation, which hinders the enolization of the α-methine hydrogen atom (circa ∼4% for the enol form). Similarly, the weaker πCH3- πPhC(O) hyperconjugative effect of the coplanar o-Me-PhC(O) moiety, in compound 2, is responsible for a slightly larger amount of the enol form (circa ∼22%), while for 4 and 5, the Cl and Br substituents lead to deviation from planarity in relation to the C=O group and only the strong -I effect plays a significant role, being responsible for the presence of larger amounts of the enol form (>50%). © 2004 Elsevier B.V. All rights reserved.
Rights: fechado
Identifier DOI: 10.1016/j.molstruc.2004.06.020
Date Issue: 2004
Appears in Collections:Unicamp - Artigos e Outros Documentos

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