Molecular structure of heterocycles. V. solvent effects on the O-17 NMR chemical shifts of 5-trichloromethyl-5-hydroxy-4,5-dihydroisoxazoles

A multi-linear-regression analysis using the Kamlet-Abboud-Taft (KAT) solva tochromic parameters in order to elucidate and quantify the solvent effects on the O-17 chemical shifts of three 5-trichloromethyl-5-hydroxy-4,5-dihyd roisoxazoles [(1a) non-, (1b) 3-methyl- and (1c) 4-methyl-substituted] are reported. The chemical shifts of ring oxygen atom, O1, of compounds 1a,b,c show depen dencies (in ppm) on the solvent polarity-polarizability of -2.4 pi*, -6.9 p i*, -4.3 pi*; on the solvent hydrogen-bond-donor (HBD) acidities -0.3 alpha , 0.6 alpha, -2.3 alpha; and the solvent hydrogen-bond-acceptor (HBA) basic ities 4.8 beta, 3.5 beta, 6.8 beta, respectively. The chemical shifts of hy droxyl oxygen atom, O5, of compounds 1a,b,c show dependencies (in ppm) on t he solvent polarity-polarizability of 26.7 pi*. 18.37 pi*, 18.5 pi*; on the solvent hydrogen-bond-donor (HBD) acidities 2.8 alpha, 2.2 alpha, 1.2 alph a; and the solvent hydrogen-bond-receptor (HBA) basicities -12. 1 beta, -10 .2 beta, -14.1 beta, respectively. The net charge and dipole moment data, o btained from MO calculations, suggest that the solvent effects on compounds 1a-c are compatible with their electronic structure.