摘要:

The vibrational distribution in the OH created by the reaction of O(1D2) atoms with NH3has been recorded directly using low pressure infrared emission spectroscopy. The relative kinetic energy of the reagents is Boltzmann at 300 K. The OH product vibrational levels are populated statistically, indicating that the reaction probably involves a long-lived ONH3intermediate. There is some evidence that this may not be the case at higher reagent translational energies.

ISSN:0008-4042    

DOI:10.1139/v86-380

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The electroreduction of bivalent metal cations may proceed by a CEE mechanism with a heterogenous chemical reaction on the electrode surface. The applications of the convolutive linear sweep voltammetry and chronoamperometry to study that mechanism are presented. The behaviour of the electrochemical reactions was simulated using an implicit finite difference technique for different values of kinetic parameters. The simulated curves were analysed and an agreement between the introduced and obtained data was found.

ISSN:0008-4042    

DOI:10.1139/v86-381

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The three possible subterminally 6-O-phosphorylated trimannosides (2–4) found on the asparagine-linked carbohydrate chains of lysosomal enzymes have been chemically synthesized as their 8-methoxycarbonyloctyl glycosides, R = (CH2)8COOCH3. The key step in the syntheses involves glycosylation of suitably protected α-D-mannopyranosides5–7with the phosphorylated mannobiosyl donor 2-O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-3,4-di-O-benzyl-6-O-di-phenylphosphoryl-α-D-mannopyranosyl chloride (14), which produced mixtures of α- and β-linked trisaccharidic products. Compounds2(αDMan(1 → 2) αDMan 6-phosphate(1 → 2)αDManOR),3(αDMan(1 → 2)αDMan 6-phosphate(1 → 3)αDManOR), and4(αDMan(1 → 2)αDMan 6-phosphate(1 → 6)αDManOR) are being used in a study of the targeting of enzymes to the lysosomes by phosphomannosyl receptors.

ISSN:0008-4042    

DOI:10.1139/v86-382

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

On the basis of the effects of the hydroxyl group on the13C nuclear magnetic resonance chemical shifts of the olefinic carbons, a new parameter was defined and a new rule was proposed for the assignment of the stereochemistry of secondary six-membered cyclic allylic alcohols.

ISSN:0008-4042    

DOI:10.1139/v86-383

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Depending on molybdenum, phenol, and acid concentrations, and time and the method of solution preparation, molybdenum and phenol can react in several ways. In 96% sulphuric acid Mo(VI) can be reduced to Mo(V) by adding solid phenol to the solution. In other cases molybdenum and phenol form stable or unstable complexes which can be in equilibrium with each other. For excess phenol the recorded spectra show two bands at around 600 and 423 nm; the first one, decreasing with time, is ascribed to the formation of an unstable complex of phenol and Mo(VI). At approximately equal concentrations of molybdenum and phenol the band at 423 nm does not appear, but two time-dependent absorption maxima are formed at 600 and 470 nm with a well defined isosbestic point at 505 nm. The complex is unstable because of the sulphonation of phenol. In 80% sulphuric acid molybdenum and phenol form a stable 1:1 complex which absorbs at 480 nm; its pKsvalue is 1.44 ± 0.03 at room temperature.

ISSN:0008-4042    

DOI:10.1139/v86-384

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The regioselective alkylation of 1,4,5-trihydroxy-9,10-anthraquinone via reaction of its leuco compound is significant for the synthesis of anthracyclinones. In the presence of pyrrolidine in toluene solution, the leuco compound3selectively forms the 4-pyrrolidino enamine11, which undergoes deamination to give 1,5-dihydroxy-9,10-anthraquinone. If an aldehyde is added, however, the enamine is alkylated, eventually yielding the 3-alky 1-1,4,5-trihydroxy-9,10-anthraquinone. Both of the above reactions of3give high yields with 100% regioselectivity. The enamine intermediate11has been trapped by oxidation to 4-pyrrolidino-1,5-dihydroxy-9,10-anthraquinone, which, after reduction, undergoes the same reactions as3giving either the alkylation or deamination product. The selective formation of11is explained in terms of an enhancement of carbonyl group electrophilicity by a relay of hydrogen bonds.

ISSN:0008-4042    

DOI:10.1139/v86-385

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The synthetic utility of hydrosilanes under the influence of trimethylsilyl-based reagents as new reducing systems is described. 1,1,3,3-Tetramethyldisiloxane (TMDS) reagent in combination with iodotrimethylsilane or bromotrimethylsilane produces alkyl halides from aldehydes in good to excellent yields. Polymethylhydrosiloxane (PMS) in the presence of iodotrimethylsilane also produces benzyl iodides in excellent yields. On the contrary, PMS reagent was found unsuitable for the synthesis of benzyl bromides. Similarly, TMDS reagent in combination with trimethylsilyl triflate produces symmetrical ethers from aldehydes without concomitant formation of competitive products. Under similar conditions, PMS reagent failed to provide the expected symmetrical ethers and Friedel–Crafts products were formed. Reduction of quinones to hydroquinones is also described.

ISSN:0008-4042    

DOI:10.1139/v86-386

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The protonation of the three nucleic acid bases, cytosine, uracil, and thymine, and of related 4-amino-2,6-dimethylpyrimidine and 2-hydroxypyridine has been studied by1H and13C nuclear magnetic resonance and ultraviolet spectroscopies mostly in 0.18–18 Maqueous sulfuric acid. The experimental data have been interpreted on the basis of the excess acidity method. The pKnvalues as well as the assigned protonation sites are discussed and contrasted with other data.

ISSN:0008-4042    

DOI:10.1139/v86-387

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

An ellipsoidal cavity model has been used to study the energy changes in occupied molecular orbitals induced by solute–solvent electrostatic interactions. Some benzene derivatives have been selected as solutes. Calculations have been carried out at the CNDO andabinitioSTO-4G levels. Important variations in the molecular orbital sequence, involving a change in the HOMO nature, have been observed. A perturbation analysis is employed to understand the orbital evolution from gas phase to solution.

ISSN:0008-4042    

DOI:10.1139/v86-388

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Using the Hartree–Fock method and, in some cases, the second order Moller–Plesset perturbational method, with 4-31G, 4-31 + G, and 4-31 + G* basis sets, a first approach to the study of the mechanism of electrochemical reduction from formaldehyde to ethanol is presented. The total energy and optimized geometry of each of the molecules involved are also given. A proton–electron–proton–electron type mechanism is proposed.

ISSN:0008-4042    

DOI:10.1139/v86-389

出版商:NRC Research Press    

年代:1986

数据来源: NRC