On carbon-13 spectra of thio- and dithiocarboxylic acids triorgano group 14 metal esters

Abstract

The thiocarbonyl carbon chemical shifts of thio- and dithiocarboxyl acid triorgano group 14 metal esters have been studied in comparison with the carbonyl chemical shifts of the corresponding carboxylic and thiocarboxylic acid derivatives. Triorgano group 14 metal groups cause remarkable downfield shifts of the carbonyl and thiocarbonyl carbon chemical shifts in the esters. The thiocarbonyl carbon chemical shifts of the dithio esters ( i-C 3H 7CS 2EMe 3, E = group 14 element) are correlated linearly with the Allred-Rochow electronegativity of the metals, and with their ππ* transition energies except for the silyl esters. The 13CO chemical shifts of trimethyltin isobutyrate appear at the lowest field in the carboxylic acid triorgano group 14 metal esters (RCOOER′ 3, E = group 14 metal). The unusual downfield shifts reflect the polymetric structure of the tin esters. The empirical equation (δ(CS) = 1.45 δ(CO)−46.5 ppm) predicting 13CO and 13CS chemical shifts, which has been proposed by Kolinowski and Kessler, can not be applied for these triorgano group 14 metal esters and ortho substituted benzoates and thio- and dithiobenzoates.