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|Type:||Artigo de periódico|
|Title:||Conformational And Electronic Interaction Studies Of Some P-substituted α-bromo-α-ethylsulfonylacetophenones|
Dal Colle M.
|Abstract:||The preferred conformations of p-substituted α-bromo-α- ethylsulfonylacetophenones Y-PhC(O)CH(Br)SO2Et (Y=OMe 1, Me 2, H 3, Cl 4, Br 5, CN 6 and NO2 7) are determined by νCO IR analysis; HF/6-31G** ab initio computations and X-ray diffraction (for 3). In the gas phase, compound 3 shows the existence of two stable conformers. The more stable and more polar c1 conformer presents the α-ethylsulfonyl and the α-bromo substituents in syn-periplanar (quasi-cis) and syn-clinal (gauche) geometries, respectively, with respect to the carbonyl group. For the second, less stable and less polar, c2 conformer, both the α substituents assume a syn-clinal (gauche) geometry. The larger stabilisation of the c1 conformer relative to c 2, in the gas phase, is attributed to the summing up of the n Br/π*CO and σC-Br/ π*CO hyperconjugative interactions and OCOδ-⋯SSO2δ+, H CH2[SO2Et]⋯OCOδ- and OSO2δ-⋯CCOδ+ orbital and electrostatic interactions, which are stronger for the c 1 conformer relative to c2. In solution, only the more polar c1 conformer has been detected, due to its stronger solvation energy relative to that of the c2 conformer. The mean carbonyl frequency shifts (Δν) close to zero, in CCl4, for the single νCO band of the title compounds 1-7 gives further support for its assignment to the c1 conformer as both the quasi-cis conformer of the α-ethylsulfonylacetophenones and the gauche conformer of the α-bromocetophenones present (Δν) values close to zero. X-ray diffraction analysis for 3 indicates that it exists in the solid state in the c′1 conformation, which is reasonably close to the c 1 one, and it is stabilised intramolecularly by the same interactions responsible for the stabilisation of conformer c1 in the gas phase. Furthermore, these molecules form centro-symmetric dimers in the crystal, which are stabilised through two pairs of intermolecular hydrogen bonds, i.e. H[o-Ph]δ+⋯OSO2δ- and H[α-CH]δ+⋯OSO2δ-. © 2004 Elsevier B.V. All rights reserved.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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