摘要:

Kinetics have been studied for the decomposition of Rh(CO)Br52−tocis-Rh(CO)2Br2−in aqueous HBr solutions at 60 °C under a carbon monoxide atmosphere. A hydrolysis step leads to formation of rhodium(I) which is stabilized as the dicarbonyl; this dicarbonyl then reacts with Rh(CO)Br52−in an autocatalytic process to give more Rh(CO)2Br2−via a mixed valence [RhI … Br … RhIII] bridged intermediate. Ferric ion may be reduced according to the net reaction:using the bromorhodate(III or I) complexes as catalyst, and the kinetics of this process are also reported.

ISSN:0008-4042    

DOI:10.1139/v77-080

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The high resolution1H nmr spectra of the substituted flavine, 3-N-methyltetraacetylriboflavine (3-Me-TARF), and its non-aqueous solution complexes with Gd(fod)3, Eu(fod)3, MoCl4, and MoCl4•2CH3(CH2)2CN, were studied in order to try to discern the binding sites of the flavine as it attaches to the molybdenum. Evidence was found that all three metal atoms, Gd(III), Eu(III), and Mo(IV), are attached in solution not only by the primary binding (chelating) sites of the flavine,viz., the O-4 and N-5 atoms, but also by an acetyl oxygen atom, at the C-4′ site of the ribityl side chain. 300 MHz spectra of the 3-Me-TARF have permitted the coupling constants for the side chain methine and methylene protons to be obtained.

ISSN:0008-4042    

DOI:10.1139/v77-081

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Dielectric absorption studies have been made of group relaxation of acetophenone, 1,4-diacetylbenzene,4-acetylbiphenyl, and 2-acetylfluorene in a polystyrene matrix, and two rigid molecules have also been examined. For acetyl group relaxation in acetophenone, ΔHE = 29.6 ± 0.6 kJ mol−1and ΔSE = 26 ± 3 JK−1mol−1(95% confidence intervals). The energy barrier for acetyl group relaxation is of the same order as that obtained from nmr data. Our results for acetophenone differ appreciably from the values reported for the gaseous phase by the far-infrared approach and from those by the dielectric absorption of aromatic ketones in benzene solution. The enthalpies of activation for acetyl group relaxation in 1,4-diacetylbenzene, 4-acetylbiphenyl, and 2-acetylfluorene are 29, 30, and 32 kJ mol−1, respectively, which values are identical within their experimental errors. These three substances have also been examined as pure solids, yielding enthalpies of activation for acetyl group relaxation of a similar magnitude.

ISSN:0008-4042    

DOI:10.1139/v77-082

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Ozonization of methylenecyclohexane in various solvents gives several peroxides and the ozonide in competing reactions. All products can be adequately explained by adaptation of the Criegee theory, without invoking a Baeyer–Villiger reaction of carbonyl solvents. Solvent effect on product proportions is not linked with dielectric constant or enol content, but appears to be a zwitterion solvation effect.

ISSN:0008-4042    

DOI:10.1139/v77-083

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The alkaline condensation ofp-hydroxyarylglycerol-β-aryl ether units in lignin with other phenolic structures and the subsequent reactions of the condensation products have been elucidated using appropriate model compounds. It is shown that the primary condensation of simple phenols (2,6-xylenol or resorcinol) into the α-position of phenolic compounds of the β-aryl ether type is followed by an aryl participation (A1-3) reaction resulting in the cleavage of the β-aryl ether bond and formation of the corresponding stilbene derivative. When resorcinol is used as reaction partner, the condensation is also followed by the cleavage of the β-aryl ether linkage through another type of neighbouring group participation reaction involving the phenolate anionorthoto the site of condensation and giving rise to the corresponding aryl-coumaran derivative.The consequences of these findings for the course of alkaline delignification processes are briefly discussed.

ISSN:0008-4042    

DOI:10.1139/v77-084

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The structure of isoflavipucine2a, a remarkable rearrangement product of the antibiotic flavipucine1, is proposed on the basis of spectral data and chemical and mechanistic considerations.

ISSN:0008-4042    

DOI:10.1139/v77-085

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

13C chemical shifts and13C–31P couplings are reported for 15 dialkylphosphonocyclohexanes. Data are compared to those for three related hydroxyphosphonates. Both direct and vicinal13C–31P couplings are useful stereochemical probes. Materials with equatorial phosphorus exhibit one bond couplings larger byca. 5 Hz than their axial counterparts. Vicinal couplings follow an approximate dihedral angle dependence but are attenuated by OH substitution. In addition to the expectedgauche-γ shielding effects, pentavalent phosphorus substituents induce minor (ca. 1 ppm) upfield shifts at carbons to which they bear ananti-periplanar relation.

ISSN:0008-4042    

DOI:10.1139/v77-086

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A series ofter-butyl peresters having a general formula corresponding to I were synthesized.The thermally initiated rates of decomposition of these peresters were determined at several temperatures and the activation parameters for these thermolyses were calculated.The rates of decomposition were relatively insensitive to the substituents and followed the order I > C2H5 > C6H5S > H > Br > Cl. The activation parameters and product studies were consistent with a simple two bond scission mechanism and no evidence could be found for neighboring group participation in these homolyses.

ISSN:0008-4042    

DOI:10.1139/v77-087

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Carbon-13, proton nuclear spin–spin coupling constants have been measured for a number of 4-substituted isothiazoles. The observed values are compared with those measured in other heterocyclic systems and those calculated in the parent and related heterocyclics using finite perturbation theory and semi-empirical molecular orbital theory at the CNDO/2 and INDO levels of approximation.

ISSN:0008-4042    

DOI:10.1139/v77-088

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Two types of reactions occur when hexaaquoiron(III) ion is irradiated at 254 nm in the presence of alcohols. Firstly, a charge transfer transition from a water centred orbital to an iron centred orbital produces OH•radicals which go on to abstract hydrogen from the alcohols. Secondly, |the reaction with the charge transfer excited states of iron(III) species can lead to outer sphere oxidation of the alcohols. In this paper, these reactions have been studied in detail for the diol ethylene glycol in aqueous solutions. It has been found that the quantum yield of acetaldehyde, the major product of hydroxyl radical reactions with ethylene glycol, is 0.09 and the yield of formaldehyde, the major product of the direct charge transfer reaction, is 0.05 in 1 Methylene glycol. The quantum yields for these major products, as well as minor products, such as glycolaldehyde and succinaldehyde, have been determined at several concentrations of ethylene glycol and iron. A detailed reaction scheme for the photolysis has been developed.

ISSN:0008-4042    

DOI:10.1139/v77-089

出版商:NRC Research Press    

年代:1977

数据来源: NRC