Data presented in this paper constitute the first nonkinetic experimental observations of nonadditive and synergistic substituent effects on the homolytic strengths of labile sp3 C-H bonds and provide evidence for the significance of solvent-induced stabilization of appropriately substituted carbon-centered radicals.The nonadditivities present in the sp3 C-H bond strengths for donor-acceptor-substituted species 4 and 6 (2 and 4 kcal/mol, respectively), although small in magnitude, are best explained by postulating that DMSO interacts with the donor-acceptor-substituted radicals 4 -H* and 6 -H* in a fashion that results in an enhanced stabilization for these species.
Experimental SectionThe syntheses of 2-8 and 10 were carried out in our laboratories and have been described previously.15'16,31 9-Methylanthracene (1, crystallized from EtOH) and phenylacetonitrile (9, distilled) were purchased from Aldrich.All of the pAf" values in Table I have been published previously; appropriate references for these values are listed in Table I.Dimethyl sulfoxide was purified and potassium dimsylate was synthesized exactly as described by Matthews and Bordwell.39 Et4N+BF4w as recrystallized from acetone and was allowed to dry at 110 °C under vacuum prior to dissolution in DMSO. Et4N*C104" was recrystallized from ethanol/water and dried under vacuum overnight prior to dissolution in DMSO.
Kinetics of the Dehydration of the β-Cages of Sodium Faujasites as Studied by H NMR Spectroscopy. -The rate of water returning from the β-cages of Na-Y-type zeolite with Si/Al ¿ 2 into the supercages is determined as a function of temp. Si/Al-ratio and cation exchange and is found to be slow and only weakly dependent on the temp. (EA = 4.1 kJ/mol). This result, which contrasts with the strongly temp.-dependent rate of penetration from the supercages into the β-cages (Ea = 100 kJ/mol), is explained by assuming the formation of a water-ion complex with a rather special arrangement of the H2O molecule. Due to spatial constraints in the . beta.-cages the complex formation entropy is negative. -(BASLER, W. D.; LECHERT, H. T.; CARBOO, D.; KNOECHEL, A.; Ber.
Acetobromglucose (I) wird mit Silbernitrat (II) und Alkoholen (III) umgesetzt und hierbei werden Mischungen aus den Glucosiden (IV) und den Salpetersäureestern (V) erhalten.
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