摘要:

Muonium atoms have been observed inn-hexane,c-hexane, and tetramethylsilane at 295 or 273 K by the MSR technique. The yield of muonium in these non-polar liquids is found to be quite comparable to that observed previously in water, methanol, and ethanol. This suggests that neither the dielectric constant of the medium nor the free-electron mobility has a major influence on the formation process. This in turn supports the view that muonium formation does not mainly result from intraspur reactions in the terminal spur of the muon's track.The chemical lifetime of muonium in these hydrocarbons is curtailed by spurious impurities so that high purity is required. In addition, however, there may be a chemical reaction between muonium and the hydrocarbon itself because the maximum lifetime found increases in the order of increasing bond energy. Reaction rate constants with added solutes have also been measured, and these observations open up the possibility of studying hydrophobic solutes and extending hydrogen-isotope studies to biologically-important media.

ISSN:0008-4042    

DOI:10.1139/v80-385

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The reaction of vitamin B12swith 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane results in the formation oftrans-4,4′-dichlorostilbene in a two-step process. In the first step, there is a nucleophilic attack by the cobalt(I) at C-1 resulting in the displacement of chloride ion and formation of an alkyl cobalamin with a chlorine atom on the α-carbon. The second step is a cobalt chloride α-elimination which proceeds through a carbenoid type intermediate that readily rearranges to the product.

ISSN:0008-4042    

DOI:10.1139/v80-386

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The crystal structure of 1-O-acetyl-17-p-bromobenzoylsideritol (ent-1α-acetoxy-16β-hydroxy-17-p-bromobenzoyloxyatis-13-ene) is presented. This crystal structure establishes unequivocally the structure of sideritol (1).

ISSN:0008-4042    

DOI:10.1139/v80-387

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

It is argued that account should be taken of Rydberg states when the course of photochemical reactions is interpreted through correlation diagrams based on the principle of conservation of orbital symmetry. This is expected to be important for molecules whose lowest excited state has Rydberg character and a symmetry different from that of the lowest valence-shell type excited state.

ISSN:0008-4042    

DOI:10.1139/v80-388

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Values of the phenolic hydroxyl content of the lignin in the secondary wall and cell corner middle lamella of the tracheids in black spruce wood were found by ultraviolet microscopy to be 0.12 and 0.06 PhOH/C9respectively. The overall value for the lignin in black spruce wood was 0.10 PhOH/C9.

ISSN:0008-4042    

DOI:10.1139/v80-389

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The crystalline conformation of inulin a (2→1)-β-D-fructofuranan has been determined based on conformational analysis coupled with X-ray and electron diffraction data. The energy contour maps as a function of three torsional angles, ψ, ω in the backbone were calculated taking into account van der Waals, torsional, and electrostatic interactions. Although several minima were observed, only two models are possible when one considers the information obtained from the diffraction data. The two models correspond to five-fold helices, one 54(left-handed) and the other 51(right-handed) with an advance per monomer of 2.16 Å, but with different conformational angles: ω = 60° and 180° respectively. Compared to the crystalline state torsion angles of polyethylene oxide analogs of inulin, large differences are noted. Steric interactions of the substituents and the exoanomeric effect are believed responsible for the observed conformational differences.

ISSN:0008-4042    

DOI:10.1139/v80-390

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The acid-catalysed hydrolysis of lactams of ring size 4–7, and ofN-ethylacetamide, has been studied at various temperatures in 0–70% aqueous sulfuric acids. The kinetics have been analysed by means of ther-hydration parameter treatment and the transition-state activity coefficient (TSAC) approach. Except for the β-lactam, all substrates show a strong positive rate dependence on water activity, indicating a tetrahedral intermediate type of mechanism, similar to that found for simple (acyclic) amide hydrolyses; only the β-lactam shows a negative rate – water activity dependence, which is interpreted in terms of a unimolecularmechanism, involving rate-determining acylium ion formation. Similarly, all substrates except the β-lactam show a pronounced destabilization of the transition-state as acidity is increased, typical of oxonium ion species. The behaviour of the β-lactam resembles that of methyl mesitoate hydrolysis. Basicity constants for lactams of ring size 4–9 show a definite dependence on ring size, with the δ-lactam being unusually basic. Both rate and pKdependence on ring size are discussed in terms of ring strain and steric effects. The activation parameters, particularly ΔS≠, are fully consistent with the conclusions drawn concerning transition-state hydration.

ISSN:0008-4042    

DOI:10.1139/v80-391

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Cholesteryl palmitate (CP) bas been incorporated into vesicles of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine/20 mol% cholesterol, in amounts up to 5 mol%. By means of31P lanthanide induced shifts the average diameter of these vesicles was calculated to be ~270 Å.The2H spectral linewidths of selectively deuterated CP incorporated into liquid crystalline dipalmitoylphosphatidylcholine vesicles are ≤ 150 Hz, implying a low degree of order for the ester acyl chain. Addition of 20 mol% cholesterol to the vesicles increases the linewidths which, nevertheless, remain ≤ 185 Hz. The corresponding2H longitudinal relaxation times (≤ 450 ms) indicate that the fast segmental motions of the ester chain are slower than for the phospholipid chains.

ISSN:0008-4042    

DOI:10.1139/v80-392

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

15N nuclear magnetic resonance chemical shifts and one-bond15N—31P couplings are reported for a series of fiveN-arylphosphoramidates and fourN-arylphosphorimidates. Results are interpreted in terms of an extensively delocalized N lone pair in the phosphoramidates, withpπ–pπdonation into the aromatic ring being dominant overpπ–dπdonation from nitrogen to phosphorus.

ISSN:0008-4042    

DOI:10.1139/v80-393

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The regiospecific (π2 + π4) cycloaddition reaction ofN-carbonyl-1,2-dihydropyridines2with nitrosobenzene afford a mixture of 3-phenyl-2-oxa-3,6-diazabicyclo[2.2.2]oct-7-ene rotamers3and4. Rotamers3and4, which differ in configuration at the carbonyl to nitrogen (amide) bond, exhibit dual resonances for C(1)H, C(5)H, and the N(6) acetyl (methoxycarbonyl) substituents. An1H nmr temperature study indicated that rotamers3aand4acoalesce at about 100 °C.

ISSN:0008-4042    

DOI:10.1139/v80-394

出版商:NRC Research Press    

年代:1980

数据来源: NRC