摘要:

Reactive silicon in waters was determined indirectly by counting101Tc after neutron activation of molybdosilicic acid (MSA) extracted with methyl isobutyl ketone (MIBK). The detection limit (defined as twice the standard deviation for the blank) was 0.2 ng mL−1. The relative standard deviation was 3% at the 10 ng mL−1level and 30% at the 1 ng mL−1level. Phosphate, arsenate, and ferric ions did not interfere by themselves. Interference from the reduction of molybdophosphoric acid by tannic acid was eliminated through the use of dichromate. The salt effect normally encountered in the analysis of sea water was examined with particular reference to silicate content of reagent salts used in preparing synthetic sea water.

ISSN:0008-4042    

DOI:10.1139/v85-429

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The synthesis of 2,2-dimethyl-5-hydroxychromene (1d) is described. The synthesis of the analogous 5,7-dihydroxy derivatives, using similar conditions, yields the adduct9derived via a Bucherer type reaction. X-ray analysis of9demonstrated that a pyrrolidine group was in the 7-position, and that the 5-hydroxyl group was involved in a strong intramolecular hydrogen bond to the 4-keto oxygen atom.

ISSN:0008-4042    

DOI:10.1139/v85-430

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A precise analysis of the1H nmr spectrum of toluene as a dilute solution in carbon disulfide yields a revised set of spectral parameters. The chemical shift of theparaproton lies 12.6 ppb to low frequency of that of theorthoprotons at 300 K. The ring proton chemical shifts are discussed and compared with1H and3H shifts observed in carbon tetrachloride. The long-range couplings between methyl and ring protons can be said to be quantitatively understood in terms of σ and σ–π electron transmitted mechanisms. The changes observed in these three couplings in phenylacetaldehyde can be quantitatively reproduced in terms of these mechanisms and also illustrate how these changes are direct measures of the conformational preferences in this molecule.

ISSN:0008-4042    

DOI:10.1139/v85-431

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

β-Tetrazolyl-trans-benzalacetophenones (T) isomerize upon heating into the corresponding azido-azomethines (A). These non-isolable products undergo various transformations depending on the reaction conditions. With organic bases such as triphenylphosphine or pyridine, their interception can occur. In aromatic solvents, a rearrangement involving loss of nitrogen leads to five-membered diazoted heterocycles:-N-benzoyl imidazoles and pyrazoles, via intermediate diazirines and oxazepines. Protic solvents have been found to facilitate the isomerisation of tetrazoles into azidoazomethines. Solvolysis of the azidooxazine and in some cases of the oxazinium species resulting from the equilibrium and reaction:are then observed.

ISSN:0008-4042    

DOI:10.1139/v85-432

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The reactions of trichloromethylium (CCl3+) with benzene and the lower alkyl aromatics (ArH) have been studied by high pressure mass spectrometry at pressures in the range 2–4 Torr and temperatures from 300 to 560 K. The only two primary products are the adduct ArHCCl3+and ArCCl2+, which is formed by loss of HCl from the adduct. The relative yields of adduct increase with increasing number of methyl substituents on the aromatic ring (benzene → mesitylene). The disappearance of CCl3+is kinetically second order with specific rate constants increasing from benzene to mesitylene, the latter reacting essentially at every ion–molecule collision. All rate constants are fairly large (>1010 cc molecule−1 s−1) and show negative temperature coefficients. ArCCl2+is unreactive but ArHCCl3+reacts further by proton transfer to ArH.

ISSN:0008-4042    

DOI:10.1139/v85-433

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The analysis of proton nuclear Overhauser effect data for piriprost, (6,9-deepoxy)-6,9-(phenylimino)-Δ6,8prostaglandin I1, indicates that the cyclopentene ring has the11Econformation. A long-range nOe effect indicates that the α-chain is folded near the pyrrole and the phenyl rings.

ISSN:0008-4042    

DOI:10.1139/v85-434

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Nitro-olefins bicycloannulate the α′-enolates of α-cyclohexenones and α-cyclopentenones by initial addition at −78 °C, followed by further reactioninsituin the presence of hexamethylphosphoramide in refluxing tetrahydrofuran to give tricyclo[3.2.1.02,7]octan-6-ones and tricyclo[2.2.1.02,6]heptan-3-ones in a single synthetic step. The reactions with 1-nitropropene and with a nitro-olefin having a more complex β-substituent are stereoselective, forming predominantly the tricyclic diastereomer in which the group derived from the β-substituent of the nitro-olefin issynto the carbonyl bridge. Based on the isolation of intermediates and side products, the mechanism of the bicycloannulation is shown to proceed via sequential kinetically controlled conjugate addition of the enolate to the nitro-olefin at low temperatures, thermodynamically controlled intramolecular Michael addition at higher temperatures to give a bicyclo[2.2.2]octanone intermediate, and hexamethylphosphoramide-assisted expulsion of the nitro group as nitrite ion with formation of the cyclopropane ring. For the first time this type of bicycloannulation has been applied to cyclopentenones, and a one-step synthesis of tricyclenone has been carried out to demonstrate the synthetic utility of this new reaction.

ISSN:0008-4042    

DOI:10.1139/v85-435

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The inclusion of clay (bentonite) (ca. 0.08–0.64 wt.%) in the lyotropic mesophase formed by potassium dodecanoate + KCl + 2H2O has been observed by2H nmr not to alter the type I CM character of the phase. Relaxation of the mesophase director has been analyzed in terms of two processes over a range of2H2O concentrations. A slow process with rate constants of ca. 2 × 10−4 − 8 × 10−4 s−1exists for the phase with clay over2H2O concentrations of 63.9–65.9 wt.%. A tenfold increase in the rate constant with an increase in the2H2O content from 62.5 to 65.5% was observed for the ternary phase at 302 K.

ISSN:0008-4042    

DOI:10.1139/v85-436

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The kinetics of autoxidation of linoleic acid in dimyristoylphosphatidylcholine (DMPC) bilayers were studied at 30 °C and pH 7 under 760 Torr O2. Reactions were initiated using either the lipid-soluble di-tert-butylhyponitrite (DBHN) or water-soluble azobis(2-amidinopropane)•HCl (ABAP). Rates of chain initiation,Ri, were measured with a lipid-soluble antioxidant, a-tocopherol, or a water-soluble one, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (Trolox). The slightly higher oxidizability obtainedcompared to methyl linoleate in chlorobenzeneis attributed to a moderate polar solvent effect on ionized linoleate near the bilayer surface. A low initiator efficiency,e = 0.0895 for DBHN in DMPC, is attributed to the cage effect in the bilayer of high microviscosity. Similar autoxidation experiments on methyl linoleate in DMPC bilayers gave a lower oxidizability, indicating that the ester is sequestered deeper in the hydrophobic region of DMPC than is ionized linoleate. Some absolute rate constants are determined using the rotating sector technique for linoleic acid in 0.50 MSDS micelles, and egg lecithin and dilinoleoylphosphatidylcholine (DLPC) bilayers. A hundredfold decrease in the termination rate constant, 2ktfor DLPC bilayer compared to homogeneous solution is attributed to chain termination in a bilayer region of high polarity. A concomitant reduction (up to tenfold) in the propagation rate constant,kp, is attributed to diffusion of polar peroxyl radicals away from the oxidizable region of the bilayer.

ISSN:0008-4042    

DOI:10.1139/v85-437

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The interaction of the two isomeric pentosesD-(−)-ribose andD-(−)-arabinose with the Ca2+ion in aqueous solution is studied with the help of two types of electrochemical cells (with and without liquid junction) including a liquid-membrane Ca2+-selective electrode. Some of theD-(−)-ribose isomers contain a sequence of hydroxyl groups which can interact specifically with the cation. The measurement of the Gibbs free energy of transfer of Ca2+between water and the sugar solutions allows one to calculate a characteristic pair-interaction parameter. This specific interaction can also be characterized by its association constant: β1 = 0.93. The two approaches are studied and their coherence is shown.

ISSN:0008-4042    

DOI:10.1139/v85-438

出版商:NRC Research Press    

年代:1985

数据来源: NRC