Effect of intramolecular and intermolecular exchange processes on the1H NMR spectra of 2-chloro-1,3,2-dioxarsolanes

The 1H and 13C NMR spectra of solutions of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxarsolane (1) and 2-chloro-1,3,2-dioxarsolane (2) are reported as a function of temperature, concentration and solvent. These data indicate rapid intramolecular conformational averaging for (1) and (2) under all the conditions investigated. Additionally, intermolecular conformational averaging processes are shown to be present. The kinetic parameters for intermolecular exchange were obtained from line shape analysis of the 1H NMR data. These results indicate the intermolecular exchange to be bimolecular in nature, involving a four-centered transition state. The OCH2CH2–O torsional angle of (2) has been calculated from the analysis of its AA′BB′ 1H NMR spectral patterns, obtained at low concentrations in the absence of intermolecular exchange.