Axial and equatorial cyclohexylacyl and tetrahydropyranyl-2-acyl radicals. An experimental and theoretical study.
Axial and equatorial cyclohexylacyl and tetrahydropyranyl-2-acyl radicals gave distinct EPR spectra thanks to surprisingly large beta-hydrogen atom hyperfine splittings that enabled them to be characterized and monitored. DFT computations indicated that the axial species (X = CH(2)) had a higher barrier to rotation about the (O)C(alpha)-C(beta) bond. The computed difference Delta H degrees for the axial and equatorial radicals (R = H, X = CH(2)) was 0.8 kcal mol(-)(1).
Restricted Rotation in a-Carbonyl Radicals
Les spectres r.s.e. de radicaux tertiaries a-carbonylCs, R,R,CCOR, (R,R2R3 = H, alcoyle) a 24°C en solution aqueuse ont rCvClCs qu'il existe une rotation completement empCchee autour du lien C-CO. L'effet est identifie par differentiation des constantes h.f.s. pour substituants R, et R2 equivalents. Les intermediaires radicalaires sont formes par des processus d'abstraction directe de fragmentation radicalaire et d'elimination reductive. [Traduit par le journal]
Thorium in monazite sand; separation and determination by precipitation from homogeneous solution
A new method is described which consists of three steps: (1) decomposition of the monazite sand with perchloric acid; (2) separation of thorium and the rare earths by hydrolysis of methyl-oxalate in acid solution; and (3) separation of thorium from the rare earths by hydrolysis of urea in the presence of formic acid. The authors consider the method to be accurate and rapid.