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Type: Artigo de periódico
Title: Spectroscopic and theoretical studies of some p-substituted alpha-ethylsulfonylacetophenones
Author: Olivato, PR
Reis, AKCA
Filho, RR
Zukerman-Schpector, J
Rittner, R
Dal Colle, M
Abstract: The preferred conformations of p-substituted alpha-ethylsulfonylacetophenones, Y-PhC(O)CH2SO2Et (Y = OMe 1, Me 2, H 3, F 4, Cl 5, Br 6, CN 7 and NO2 8) are determined by v(CO) IR analysis, HF/6-31G** computations (1, 3, 5, 7 and 8) and X-ray diffraction for 5 and 7. The match between IR frequencies and intensities of the carbonyl doublet components in carbon tetrachloride (first overtone) and the results of the calculations indicates that the lower frequency component corresponds to the more stable gauche (g) conformer, while the higher frequency component is related to the quasi-cis (q-c) one. The gauche conformer (g) (ca. 85%) prevails over the quasi-cis conformer (q-c) population, and the q-c/g population ratio increases on going from electron-attracting to electron-donating substituents, both in the gas phase and in solution. These trends are discussed in terms of O(SO2)delta-...C(CO)delta+ charge transfer (CT), O(CO)delta-...S(SO2)delta+ (Coulombic interaction), (H\CH2(Et)\delta+...O(CO)delta), Hdelta+(2')((p-Ph))O-...((CO))delta and Hdelta+(6')((o-Ph))O-...((SO2))delta- hydrogen bonds and electrostatic interactions, along with the pi(CO)/sigma(C-S)* and pi(CO)/sigma(C-S) orbital interactions, which stabilise the g rotamer. The stabilisation of the q-c rotamer through O(CO)delta-...S(SO2)delta+ (CT), Hdelta+(2')((o-Ph))O-...((CO))delta- (CO H(CH2(Et)]delta+...O(CO)delta- hydrogen bond interactions is counterbalanced by O(CO)delta-...O(SO2)delta- electrostatic repulsion, which destabilises significantly this rotamer. The X-ray diffraction analyses show that 5 and 7, in the solid, adopt the cis (c') conformation, which is stabilised through intermolecular hydrogen bonds involving the acidic alpha-methylene Hdelta+(3A), H(3B) and m-phenyl Hdelta+(5')([m-Ph]) hydrogen atoms and the Odelta-(6), Odelta-(7) sulfonyl and Odelta-(1) carbonyl oxygen atoms. (C) 2004 Elsevier B.V. All rights reserved.
Subject: infrared spectroscopy
conformational analysis
ab initio calculations
X-ray diffraction analysis
Country: Holanda
Editor: Elsevier Science Bv
Citation: Journal Of Molecular Structure-theochem. Elsevier Science Bv, v. 677, n. 41699, n. 199, n. 209, 2004.
Rights: fechado
Identifier DOI: 10.1016/j.theochem.2004.01.032
Date Issue: 2004
Appears in Collections:Unicamp - Artigos e Outros Documentos

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