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Type: Artigo de periódico
Title: Conformational and electronic interaction studies of some p-substituted alpha-bromo-alpha-ethylsulfonylacetophenones
Author: Olivato, PR
Reis, AKCA
Zukerman-Schpector, J
Rittner, R
Dal Colle, M
Abstract: The preferred conformations of p-substituted alpha-bromo-alpha-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 v(CO) 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 c, conformer presents the alpha-ethyl sulfonyl and the alpha-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, c(2) conformer, both the a substituents assume a syn-clinal (gauche) geometry. The larger stabilisation of the c(1) conformer relative to c(2), in the gas phase, is attributed to the summing up of the n(Br)/pi(CO)* and sigma(C-Br)/pi(CO)(*) hyperconjugative interactions and OCOdelta-...SSO2delta+, H-CH2[SO2Et](...) O-CO(delta-) and OSO2delta-...CCOdelta+ orbital and electrostatic interactions, which are stronger for the c(1) conformer relative to c(2). In solution, only the more polar c(1) conformer has been detected, due to its stronger solvation energy relative to that of the c(2) conformer. The mean carbonyl frequency shifts (Deltav) close to zero, in CCl4, for the single v(CO) band of the title compounds 1-7 gives further support for its assignment to the c(1) conformer as both the quasi-cis conformer of the alpha-ethylsulfonylacetophenones and the gauche conformer of the alpha-bromocetophenones present (Deltav) 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 cl one, and it is stabilised intramolecularly by the same interactions responsible for the stabilisation of conformer cl 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](delta+..) O-SO2(delta-) and H[alpha-CH]delta+...OSO2delta-. (C) 2004 Elsevier B.V. All rights reserved.
Subject: infrared spectroscopy
conformational analysis
ab initio calculation
Country: Holanda
Editor: Elsevier Science Bv
Citation: Journal Of Molecular Structure-theochem. Elsevier Science Bv, v. 671, n. 41699, n. 97, n. 104, 2004.
Rights: fechado
Identifier DOI: 10.1016/j.theochem.2003.10.059
Date Issue: 2004
Appears in Collections:Unicamp - Artigos e Outros Documentos

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