摘要:

NF3is found to form a type I clathrate hydrate with a Pm3ncubic unit cell dimension of 11.91 Å at 110 K and a dissociation pressure of 16.5 atm at 0 °C. Dielectric studies below 100 K give, for reorientation of the NF3dipole in the structure I cages, an average activation energy of 0.79 kcal mol−1. Well-resolved absorption peaks arising from NF3incorporated in small and large cages of the structure II hydrate formed with SF6give activation energies of 1.05 and 0.29 kcal mol−1, respectively.19F nmr lineshapes show in addition the presence of faster reorientation about the NF3symmetry axis which is not completely removed even at 1.6 K. The pronounced effect of molecular oxygen impurity on the nmr linewidths at high magnetic fields and very low temperatures is discussed.

ISSN:0008-4042    

DOI:10.1139/v84-204

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

An X-ray crystallographic study of merosinigrin confirmed the structure as 1,2-S,O-(1R,2S-1-cyano-2-methyl-1,2-ethanediyl)-1-thio-β-D-glucopyranose. The compound crystallizes in the space groupP1 witha = 6.699(1),b = 9.347(1),c = 5.328(2) Å, α = 103.56(2), β = 109.14(3), γ = 86.71(1)°, andZ = 1. The structure was refined by full-matrix least-squares techniques to a final agreement value ofR = 0.031. Merosinigrin provides what appears to be the first example of the anomeric effect in a thiane (1,4-oxathiane) system with cyano as the polar substituent.

ISSN:0008-4042    

DOI:10.1139/v84-205

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Some ruthenium(III) complexes Ru(porp)(L)X and [Ru(porp)L2]X, (porp = dianion of octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP); L = PPh3, P″Bu3; X = Br, Cl) have been prepared from the precursor complexes Ru(porp)L2or Ru(porp)(CO)L using as oxidant the halogens, or air in the presence of the hydrogen halides. The X = PF6salts can be made using Et3O+PF6−as oxidant. Ruthenium(II) porphyrin π-cation radical intermediates have sometimes been detected. The X-ray crystal structure of Ru(OEP)(PPh3)Br, the first reported for a ruthenium(III) porphyrin, reveals that metal is displaced 0.049 Å from the plane of the pyrrole N atoms towards the phosphine. The Ru(OEP)(py) Br and [Ru(OEP)(py)CH3CN]PF6complexes have been synthesized from Ru(OEP)(CO)py. The ruthenium(III) complexes are low-spin as shown by magnetic and esr data. Optical and1H nmr data, the latter showing large paramagnetic shifts, are also presented.

ISSN:0008-4042    

DOI:10.1139/v84-206

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Aqueous solutions of sodium dibutylphosphate (NaDBP) give rise to lamellar liquid crystalline phase between 280 and 340 K for NaDBP concentrations ranging from 3 to 4 mol L−1. The orientation and dynamic behaviour of several paramagnetic probes such as the vanadyl ion, tempoamine, tempone and tempobutanamide dissolved in this phase have been investigated by esr.The vanadyl ion binds to the phosphate group, forming a complex, thezmagnetic axis of which is on the average perpendicular to the lamellar plane. The molecular mobility at the H2O/DBP−interface is given by the reorientation correlation time of thezaxis, which is derived from the total width of the spectrum, using the empirical relation. The parametersa = 2.95 × 10−11 s andb = −1.42 are obtained from the viscosity dependence of the esr line widths and of the anisotropic hyperfine couplings.The tempone and tempoamine are localized in the polar domains of the mesophase, reorienting rapidly about the N—O direction which is, on the average, parallel to the director of the lamellar plane. The anisotropic motion of these radicals is assigned to hydrogen bonding which occurs, according to the cases, with water molecules or phosphate groups. Some correlations are established between the esr of spin probes and2H and31P nmr experiments on substrate molecules.

ISSN:0008-4042    

DOI:10.1139/v84-207

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Nitrogen-14 quadrupole interactions have been observed in the nonexchanging amino proton1H nmr spectra of rigorously purified liquid mono- and dimethylamines over the temperature range −82 °C to +81 °C. The proton lineshapes have been analyzed to yield14N spin-lifetimes (τ) as a function of temperature. Activation energies and correlation times for molecular reorientation in the liquids have been calculated from these data and the results compared with those from14N nmr measurements.

ISSN:0008-4042    

DOI:10.1139/v84-208

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

We examine Flory's RAfmodel of polymerization for a finite closed system ofNmonomers. Monomers haveffunctional groups of type A. Random stepwise reaction between A's, regardless of ring formation, bonds the monomers together.We give exact statistics for the resulting polymer distribution and verify the results of the Falk and Thomas computer simulation. AsN → ∞, Flory's modification of the Stockmayer distribution gives the distribution of finite polymers, and cyclization is confined to the gel.Similar results hold for Flory's AgRBf−gmodel.

ISSN:0008-4042    

DOI:10.1139/v84-209

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Reaction of solvated electrons with nitrobenzene, N, is nearly diffusion controlled in both pure solvents;kN ~ 1010 dm3/mol s. The value ofkNis approximately proportional to the inverse viscosity η−1in the pure solvents, and in the mixed solvents at different temperatures. However, on going from zero to 74 mol% water at the same temperaturekNis independent of the 40% increase of η. Electron diffusion in the mixed solvents is not a simple function of fluidity.Reaction with the inefficient scavengers tryptophane (kS ~ 109 dm3/mol s) and phenol (kS ~ 107–108 dm3/mol s) correlates inversely with the electron optical absorption energy. The latter is related to the trap depth in the solvent; electrons in deeper traps have less tendency to react with molecules of low electron affinity.Addition of 3 mol% 2-PrOH to water at 296 K increases the value of Gϵmaxby 16%, although the value in pure 2-PrOH is three-fold smaller than that in pure water. The increase is attributed to an increase in the free ion yield, caused by an increase in the product of the electron thermalization range and the microscopic dielectric constant of the fluid between the ion and electron, averaged over the time that they exist as a correlated pair. Addition of a small amount of alcohol to water increases the orderliness of the water structure.

ISSN:0008-4042    

DOI:10.1139/v84-210

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The crystal and molecular structure of the title compound are described. Crystals are orthorhombic, space groupPna21,a = 10.977(3),b = 6.489(2),c = 9.811(2) Å,Z = four molecules per cell. Atom C(4), to which the hydroxyl group is attached, appears to have been moved outwards (away from hydroxyl). This resembles similar movements inchair–chairbicyclo[3.3.1]nonanes where intramolecular repulsion is thought to be responsible. In the present molecule, however, the more likely cause is the presence of an intermolecular hydrogen bond.

ISSN:0008-4042    

DOI:10.1139/v84-211

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The Photo-Fries rearrangement of eight anilides on the surface of dry silica gel has been examined. The rearrangement occurs quite cleanly, giving somewhat more of theparaisomer than that obtained in methanolic solution. A test for intermolecularity on the silica gel surface showed that, as in solution, the radical pair intermediates do not separate. This contrasts with the behaviour of a previously reported dibenzyl ketone derivative.

ISSN:0008-4042    

DOI:10.1139/v84-212

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The influence of heat treatment and of added coadsorbates on the surface photophysics of pyrene and naphthalene adsorbed on silica gel is reported. When the silica gel surface is partially dehydroxylated, the distribution of pyrene or naphthalene is inhomogeneous, as indicated by multiexponential fluorescence decay and broad emission spectra. Addition of polar coadsorbates renders the surface more homogeneous with singlet lifetimes approaching solution values. The pretreatment and addition of coadsorbates, in the case of pyrene, also influence the relative importance of dynamic excimer formation vis-a-vis ground state association.

ISSN:0008-4042    

DOI:10.1139/v84-213

出版商:NRC Research Press    

年代:1984

数据来源: NRC