摘要:

The rotation–vibration relaxation of a mixture of a diatomic gas (approximately simulating hydrogen) with an inert gas is studied both by direct integration, and by an approximate linearised normal-mode method. It is shown that although the linearised normal-mode approximation is a powerful aid to understanding these processes, its numerical accuracy is limited to high dilutions (e.g. 1% of X2in M) and to times shorter than the final relaxation time.Direct numerical integration of the relaxation equations for various mixture ratios shows that the plot of vibrational relaxation rate constant vs. mole fractionxis non-linear, and that the slope of this plot nearx = 0 can be correlated with the rates of the R–R processes,notthe V–V processes as is normally assumed. A brief discussion is presented of the conditions under which the linear mixture rule for relaxation is rigorously obeyed: as is the case for chemical reaction, these conditions are impossibly stringent.An appendix presents a comparison of the transition probabilities used in this series of papers with those recently obtained by Tarr and Rabitz for the relaxation of hydrogen in argon.

ISSN:0008-4042    

DOI:10.1139/v79-183

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Reaction of trimethylthioborate, B(SMe)3, with triisothiocyanatoborane, B(NCS)3, at room temperature gives mixtures containing B(SMe)3, the mixed compounds B(NCS)(SMe)2and B(NCS)2(SMe) in low concentration, and association compounds. The previous compounds cannot be isolated due to equilibria being set up. Mass spectrometry, infrared and nmr data are reported. Structures involving S–B donor–acceptor bonds between the monomers are proposed for the association compounds {B(NCS)2(SMe)}2, {B(NCS)2(SMe)}2{B(NCS)3}, and {B(NCS)2(SMe)}2{B(NCS)3}2. Reaction of these compounds with trimethylamine yields Me3NB(NCS)3and Me3NB(NCS)2(SMe). The same reaction with dimethylsulphide is incomplete and yields only Me2SB(NCS)3. Acidity strength decreases in the order B(NCS)3 > B(NCS)2(SMe) > B(NCS)(SMe)2 > B(SMe)3. This trend explains why dimerization of B(NCS)2(SMe) occurs whereas B(NCS)(SMe)2is unassociated.

ISSN:0008-4042    

DOI:10.1139/v79-184

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The electrical conductibilities of 19 1-1 MX electrolytes (M = alkaline, quaternary ammonium; X = perchlorate, halide, nitrate) in water–hexamethylphosphotriamide mixtures at 25 °C has been measured. The individual conductibilities of 17 monovalent ions in these mixtures were calculated using the hypothesis of ion equimobility in Bu4NBPh4. Following a critical review of the traditionally used methods, it has been shown that, from these results, Zwanzig's theory alone allows the objective assessment of ion–solvent interactions. However, this theory at its present state of development cannot be used to elucidate all the problems (because Zwanzig considers the displacement of the free ion) but it does distinguish the nature of the interactions between an ion and the solvent, depending on the mobility of that ion.

ISSN:0008-4042    

DOI:10.1139/v79-185

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The adsorption and association of cytidine sulphate have been studied by using phase-sensitive ac-polarography in acidic buffer solution (pH 3.24) at the dropping mercury electrode. At low bulk concentrations, adsorbed molecules of cytidine sulphate at maximal adsorption potential (−0.7 V) are orientated in 'dilute' adsorption layer planar to the electrode surface where the interaction of π-electrons with interface favours adsorption. At bulk concentrations above a threshold value (6.6 × 10−3 M), the stacking interactions between vertically oriented molecules lead to association and formation of a compact layer; and a pit is observed. The concentration dependence of the ac-capacity current at a maximal adsorption potential (−0.7 V) shows a two-step Frumkin isotherm due to association of the adsorbed molecules. The adsorption parameters are computed and discussed.

ISSN:0008-4042    

DOI:10.1139/v79-186

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Extractive-free aspen wood meal was subjected to autohydrolysis at 195 °C for 5 min to 2 h, and the lignin extracted with 90% dioxane. Extracted autohydrolysis lignin was found to be higher in carbon but lower in hydrogen and oxygen content than aspen milled wood lignin. The methoxyl content was also lower than the reference lignin. These differences have been attributed to condensation and incorporation into the lignin of non-lignin components. A lignin extractability curve with a maximum delignification at autohydrolysis time of 30–40 min was found. From molecular weight distribution studies the ratio of high molecular weight to low molecular weight materials varied for the different extracted lignins and reached a maximum at autohydrolysis time of 40 min. A mechanism of depolymerization/repolymerization of the lignin via carbonium ions has been proposed.p-Hydroxybenzoic acid is postulated as contributing to the extractability of aspen lignin by acting as a blocking agent.

ISSN:0008-4042    

DOI:10.1139/v79-187

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The•CO2−radical has been generated by photolysis of a solution of sodium peroxydisulfate containing sodium formate and by hydrogen abstraction using TiCl3and H2O2in the presence of sodium formate. In both cases, the inclusion of DMPO resulted in the formation of a spin adduct withaN = 15.8 G,aβH = 19.1 G, andg = 2.0058 which is assigned to the•CO2−adduct. In addition the DMPO adduct of SO4−•is presented. Finally, it is shown that DMPO can react with anionic radicals and that the resultant spin adducts are themselves highly dissociated.

ISSN:0008-4042    

DOI:10.1139/v79-188

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Reaction of 2-amino-3-nitropyridine with acid chlorides in the presence of dimethyl sulfoxide and a tertiary base, such as pyridine, unexpectedly yielded the aminalN,N′-bis(3-nitro-2-pyridinylimino)methylene5. A similar aminal6formed when 2-amino-5-nitropyridine was treated under the same conditions. However, simple aminopyridines such as 2-aminopyridine or 2-amino-6-methylpyridine gave only the 2-N-methylenethiomethyl derivatives. It was proved that the aminals are formed by the attack of a suitable base on theN-methylenethiomethyl intermediates with expulsion of methyl mercaptan. The formation of these unusual aminals may be explained to be taking place via a Pummerer type rearrangement.

ISSN:0008-4042    

DOI:10.1139/v79-189

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Several diimines have been synthesised from the reaction of substituted imines with sodium in dry ether followed by bubbling in oxygen and subsequent protonation. A probable mechanistic route for the formation of products through the dimerisation of initially formed anion radicals is presented and an alternative route, through the dimerisation of radicals formed by hydrogen abstraction from starting imine, has been excluded by substituent labelling experiments. Ketone hydrazones on treatment with sodium in ether and subsequent air oxidation gave substituted diazomethanes in excellent yields (88–95%).

ISSN:0008-4042    

DOI:10.1139/v79-190

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The mass spectral fragmentation patterns of bis(trimethylsilyl)- and bis(trimethylgermyl)carbodiimides are compared. Metastable confirmed transitions involve elimination of neutral fragments apparently containing Si=N and/or Si=C bonds. The fragmentation pathways are similar for the germyl analogue but no proof of a fragment containing a Ge=C bond was observed.

ISSN:0008-4042    

DOI:10.1139/v79-191

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A method was devised for estimating relative contributions to atom recombination from the bound complex and triple collision mechanisms. The method is based on three assumptions: a collinear model is valid, recrossings of a suitably chosen transition state surface equally affect both contributions to the recombination rate, and the two contributions correspond to crossings of parts of the transition state surface which differ only in total energy. Ratios of the rate constants for recombination by the two mechanisms were calculated for a classical model of Br and I atom recombination in rare gases. The ratios had already been obtained for the model from three-dimensional trajectory calculations. The results disagreed by as much as a factor of ten for helium as the third body, but they were within 50% or better for xenon. It was argued that the discrepancies are largely due to a breakdown of the second of the foregoing assumptions. The formula for the rate constant for recombination by both mechanisms together was extended to three dimensions at the expense of introducing an adjustable parameter. The extended formula was found to give results in agreement with the trajectory calculation to within 30% or better.

ISSN:0008-4042    

DOI:10.1139/v79-192

出版商:NRC Research Press    

年代:1979

数据来源: NRC