摘要:

Lithium is atomised in an air–acetylene flame within a longitudinal magnetic field. Birefringent and dichroic signals are separately measured using a pulsed hollow cathode source. The arrangement is found to give isotopic selectivity and is useable down to concentrations of about 10 μg/mL. The signal ratio of birefringence: dichroism is found to be approximately independent of sample concentration at the high and low extremes of the calibration curve. However, severe distortions occur at intermediate concentrations. In addition, a reversal of signal magnitudes is observed between6Li and7Li. This effect is attributed primarily to a distortion of the source profile as a result of self-absorption.

ISSN:0008-4042    

DOI:10.1139/v87-152

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The1H nuclear magnetic resonance spectra for CCl4solutions are analyzed for 2-(thioethyl)phenol, 2,3-dimethoxyphenol, and 8-hydroxythiochroman. The chemical shifts of the hydroxyl protons in these compounds, in 2,3-dihydroxyanisole, and 2-hydroxybenzyl methyl ether are discussed in terms of stereospecific intramolecular OH hydrogen bonds to lone-pair electrons on oxygen and sulfur. The O—H … O hydrogen bonds can be adequately discussed in terms of equivalent lone pairs on oxygen. There is very little difference between the hydrogen bond energies for 2,3-dihydroxyanisole and 2,3-dimethoxyphenol. In the latter the central hydrogen bonded methoxy group lies nearly perpendicular to the ring plane. The O—H … S hydrogen bonds are best described in terms of nonequivalent, 3sand 3p, lone pairs on sulfur. It is estimated that an O—H … H 3shydrogen bond is at least 8 kJ/mol weaker than an O—H … 3phydrogen bond. The former is predominant in the thiochroman derivative and the latter in the thioethylphenol, in which the thioethyl group prefers a plane perpendicular to the benzene ring. The long-range benzylic coupling constants in the thiochroman derivative indicate inversion of the saturated ring between distorted half-chair conformations. The boat conformation can be ruled out.

ISSN:0008-4042    

DOI:10.1139/v87-153

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Two fractions of (soluble) manganese in Lake Ontario water have been detected and measured with the aid of sequential preconcentration on the polyacrylic ester resin, XAD-7, and Chelex-100. One fraction, consisting of free Mn(II), was retained on the XAD-7 column; the second fraction, consisting of one or more unidentified forms, was retained on Chelex-100. After elution from the columns, the concentration of manganese in each fraction in the lakewater was determined by graphite-furnace AAS. Because both fractions are retained by Chelex-100, the second fraction could also be determined by difference on passage of two separate aliquots through Chelex-100 and XAD-7. Analysis of samples from three locations in the western basin of Lake Ontario showed that about 12–22% of total (soluble) manganese was present as free Mn(II).

ISSN:0008-4042    

DOI:10.1139/v87-154

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

A versatile thin layer spectroelectrochemical cell employing specular reflection of the incident light beam from the electrode surface is described. Its application to in-situ uv–vis and FTIR characterization of the products of electrochemical reactions and to thin layer voltammetry and coulometry as well as conventional cyclic voltammetry is demonstrated for the oxidation of tetraphenylporphinatozinc in dichloroethane/tetrabutylammonium perchlorate solution. The advantages and disadvantages of this type of cell as compared to more conventional sandwich type optically transparent thin layer electrodes are discussed.

ISSN:0008-4042    

DOI:10.1139/v87-155

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Evidence has been obtained by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) for the existence of hydronium ions on the surfaces of hydrated single crystals. The band near 1740 cm−1due to the ν4(e) bending vibration of the hydronium ion has been identified on silicon, germanium, thallium bromide iodide (KRS-5), and zinc selenide single crystals. The protonating capability of these hydronium ions was demonstrated with pyridine derivatives.

ISSN:0008-4042    

DOI:10.1139/v87-156

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Dialkyldithiocarbamate derivatives (R2NCS2)nM of a number of metals (M = Fe, Co, Ni, Cu, Ag, Zn, Cd, In, Tl) have been synthesised in good yield by electrochemical oxidation of appropriate sacrificial anodes in non-aqueous solutions of either the corresponding tetraalkylthiuram disulphide (R2NCS2)2(R = Me, Et) or a mixture of carbon disulphide plus the secondary amine R2NH (R = Et,i-Pr; R2NH = piperidine). Similar experiments with solutions of (EtO)2P(S)SH (= HL) gave MLn•derivatives (M = Fe, Co, Ni, Cu, Ag, Au, Zn, Cd, Hg, Ga, In, Tl) while in the presence of HL + 1,10-phenanthroline, MLn•phen derivatives were obtained for M = V, Mn, Fe, Co, Zn, and Ga.

ISSN:0008-4042    

DOI:10.1139/v87-157

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Reaction of (E,Z)-or (E)-2-anisyl-1,2-ditolyl[2-13C]vinyl bromides ((E,Z)- or (E)-6-Br-2-13C) with HOAc–AgOAc gave a 1:1 mixture of (E)- and (Z)-2-anisyl-1,2-ditolyl[1,2-13C]vinyl acetates ((E,Z)-6-OAc-1,2-13C), with about 37.4% scrambling of the label from C-2 to C-1 arising from degenerate 1,2-anisyl shifts in the 2-anisyl-1,2-ditolyl[2-13C]vinyl cation (6-2-13C). No detectable amount of 1-anisyl-2,2-ditolylvinyl acetate was formed, indicating no nondegenerate 1,2-tolyl shift in cation6to give the more stable 1 -anisyl-2,2-ditolylvinyl cation (10) in the reaction with HOAc–AgOAc. Reaction of (E)-6-Br-2-13C with 2,2,2-trifluoroethanol (TFE) in the presence of 2,6-lutidine gave as major product 1-anisyl-2,2-ditolyl[1,2-13C]vinyl 2,2,2-trifluoroethyl ether (10-OTFE-1,2-13C) and a 1:1 mixture of (E)- and (Z)-2-anisyl-1,2-ditolyl[1,2-13C]vinyl 2,2,2-trifluoroethyl ethers ((E,Z)-6-OTFE-1,2-13C) as minor products, the ratio of10-OTFE to (E,Z)-6-OTFE being about 80:20. Scrambling on the13C label in the major product,10-OTFE-1,2-13C, was 48.8 ± 0.9% and scrambling in the minor products, (E,Z)-6-OTFE-1,2-13C, was 47.2 ± 1.4%. The present work with cation6completes the series of nine possible triarylvinyl cations, with various combinations of phenyl (Ph),p-tolyl (Tol), and (or)p-anisyl (An) as the three aryl groups, that can give rise to degenerate 1,2-aryl shifts across the double bond, and the present results are discussed in conjunction with data from previous work on the other eight triarylvinyl cationic systems.

ISSN:0008-4042    

DOI:10.1139/v87-158

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The static13C nmr powder pattern for solid ammonium thiocyanate is analyzed to obtain the13C chemical shielding anisotropy, 321 ± 7 ppm, and the13C–14N dipolar splitting, 1295 ± 25 Hz. Slow magic angle spinning15N nmr experiments are analyzed to obtain a nitrogen chemical shielding anisotropy of 415 ± 15 ppm. The13C–14N dipolar splitting leads to an effective C—N bond length of 1.19 ± 0.01 Å, in good agreement with the value of 1.176 Å reported from accurate X-ray and neutron crystallographic studies. In solid NH4NCS absolute values of the average shielding constantsand ctare 52 and 34 ppm, respectively. Comparison of calculated and observedvalues indicates that intermolecular interactions decrease the13C and15N shielding constants by approximately 10 and 30 ppm, respectively.

ISSN:0008-4042    

DOI:10.1139/v87-159

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The need for a rapid method for detecting sulphate sulphur in coconut and caffeine in manufactured tea initiated a study to compare high performance liquid chromatography with classical methods. We compare the methods in their applicability in rapid and selective analysis of coconut water, plant tissues, and soil, as well as of caffeine in tea samples from different regions. We present a statistical correlation between the methods and discuss the significance of our results.

ISSN:0008-4042    

DOI:10.1139/v87-160

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Rotational correlation times for the end-over-end rotation of theC3symmetry axis of the nitrate anion in the temperature range 3–80 °C are studied by nuclear magnetic resonance spectroscopy for a variety of nitrate salts in aqueous solution. The counterion is found to retard the rotation of the anion in the following order: Sc3+ > La3+ > Pb2+ > Ca2+, Sr2+ > Al3+, K+, Na+, (CH3)4N+ > Zn2+, Mg2+, Li+, NH4+, H3O+. This relative order is discussed in terms of the association of the nitrate ion with the cation. Oxygen-17 nmr spin-lattice relaxation times in combination with14N nmrT1values are used to derive rotational diffusion constants for the in-plane rotations of the nitrate anion. In all cases the in-plane rotations are found to be slower than the corresponding end-over-end motion.

ISSN:0008-4042    

DOI:10.1139/v87-161

出版商:NRC Research Press    

年代:1987

数据来源: NRC