2001•Spectroscopy LettersRequires access
MOLECULAR STRUCTURE OF HETEROCYCLES. V. SOLVENT EFFECTS ON THE 17O NMR CHEMICAL SHIFTS OF 5-TRICHLOROMETHYL-5-HYDROXY-4, 5-DIHYDROISOXAZOLES†
Marcos A. P. Martins, Rogério Antônio Freitag, Nilo E. K. Zimmermann, Adilson Paulo Sinhorin, Wilson Cúnico, Giovani P. Bastos, Nilo Zanatta, Hélio G. Bonacorso
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Abstract
A multi-linear-regression analysis using the Kamlet- Abboud-Taft (KAT) solvatochromic parameters in order to elucidate and quantify the solvent effects on the 17O chemical shifts of three 5-trichloromethyl-5-hydroxy-4, 5-dihydroisoxazoles [(1a) non-, (1b) 3-methyl- and (1c) 4-methyl-substituted] are reported. The chemical shifts of ring oxygen atom, O1, of compo- unds 1a, b, c show dependencies (in ppm) on the solvent polarity-polarizability of −2.4π*, −6.9π*, −4.3π*; on the solvent hydrogen-bond-donor (HBD) acidities −0.3α, 0.6α, −2.3α; and the solvent hydrogen-bond-acceptor (HBA) basicities 4.8β, 3.5β, 6.4β, respectively. The chemical shifts of hydroxyl oxygen atom, O5, of compounds 1a, b, c show dependencies (in ppm) on the solvent polarity-polarizability of 26.7π*, 18.3π*, 18.5π*; on the solvent hydrogen-bond-donor (HBD) acidities 2.8α, 2.2α, 1.2α; and the solvent hydrogen-bond-acceptor (HBA) basicities −12.1β, −10.2β, −14.1β, respectively. The net charge and dipole moment data, obtained from MO calculations, suggest that the solvent effects on compounds 1a-c are compatible with their electronic structure.