摘要:

Some rate data are reported for deuterium exchange between water and hydrogen using series of platinum–silica catalysts. Three different methods of preparing catalysts were used to give different series of metal particle sizes. Within each series, the particle size was increased by sintering batches in air, at temperatures up to 700 °C. These methods produced platinum particles ranging from 5 to 250 Å in diameter. Metal surface areas and particle sizes were measured by hydrogen chemisorption, X-ray diffraction, and electron microscopy.The specific rates,i.e., rates per unit surface area of platinum varied by a factor of three within each series, reaching a maximum for sintering temperatures of about 500 °C. These maximum rates, measured at 127 °C with a water-to-hydrogen ratio of 0.31, varied from 1.9 × 10−8to 5 × 10−8 mol D2 cm−2s−1. Thus no effect of particle size on rate was observed, and the differences noted are ascribed to other effects of the methods of preparing the catalysts.

ISSN:0008-4042    

DOI:10.1139/v71-572

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

Crystals of dichlorobis(4-methylpyridine)zinc(II), Zn(4-CH3Py)2Cl2, are monoclinic, space groupP21/c, witha = 14.294(13),b = 7.885(8),c = 13.473(11) Å, β = 100.60(5)° and 4 molecules in the unit cell. The final atomic parameters were obtained from a block-diagonal least squares refinement using anisotropic thermal parameters. The hydrogen atom positions were established but the parameters were not refined. The final agreement residual for 1348 observed reflections isR = 0.043. The zinc atom is tetrahedrally coordinated.

ISSN:0008-4042    

DOI:10.1139/v71-573

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

A new ligand, 2,3-di(2-pyridineN-oxide) quinoxaline and its complexes with copper(II), cobalt(II), and nickel(II), have been prepared. A detailed investigation of the magnetic and spectral properties of these compounds has led to some tentative suggestions as to their structures.

ISSN:0008-4042    

DOI:10.1139/v71-574

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

The stereochemistry of dehydrogenation of the primary carbinol group ofD-galactose byD-galactose oxidase has been determined. UsingD-galactose-6-dand methyl β-D-galactopyranoside-6-d, it has been established that the reaction involves removal of thepro-S6-hydrogen atom. This conclusion is based on product analysis, and on the relative impact of the deuterium isotope effect on oxidation rates of substrates having differentR:Sdeuteration patterns. The absolute configurations at C-6 of these substrates have been determined by selective chemical transformations to products of known configuration. The rotational conformation of the 6-carbinol group ofD-galactose and its possible relationship to the specificity of the enzyme are discussed, as well as the stereochemistry of reductive deuteration ofaldehydosugar derivatives.

ISSN:0008-4042    

DOI:10.1139/v71-575

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

The n.m.r. spectra of eight 1,2-dihaloalkanes have been determined in solvents of differing polarity. The relative rotamer stabilities for each compound have been deduced from the variation of the difference and sum of vicinal coupling constants with solvent. Variations in geminal and long range coupling constants with solvent are also attributed to conformational changes.

ISSN:0008-4042    

DOI:10.1139/v71-576

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

2,3-Diphenylindenone oxide1undergoes thermal 1,3-dipolar cycloadditions via a carbonyl ylide with symmetrical olefinic dipolarophiles to give (i) withcisaddends mixtures ofendoandexoadducts in whichendoadducts generally predominate in agreement with results obtained with 1-cyclohexyl-6-(cyclohexylimino)-1a-phenylindano [1,2-b]aziridine and (ii) withtransaddends adducts in which the2-exo-3-endoproduct predominates. The pyrilium oxide4is efficiently trapped with benzyne. 1,3-Diphen-ylisobenzofuran reacts withcis-addends to giveendo–exomixtures in which theendoadducts generally predominate. 2-Acetyl-5,5-pentamethylene-2-phenyl-Δ3-1,3,4-oxadiazoline undergoes regiospecific cycloaddition via a carbonyl ylide with unsymmetrical olefinic dipolarophiles in accordance with substituent electronic effects, and with 1,4-naphthoquinone a previously postulated type of intermediate adduct is isolated.

ISSN:0008-4042    

DOI:10.1139/v71-577

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

A number of silylsuccinimides containing silicon substituants —H, —CH3, —C2H5, —CH=CH2, —CH2CH=CH2, —C6H5, as well as disuccinimides, have been prepared and characterized by i.r., n.m.r., and mass spectrometry. The results are compared with previous studies of silylphthalimides.

ISSN:0008-4042    

DOI:10.1139/v71-578

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

Differences in heats of solution and in heats of dilution of electrolytes in H2O and D2O were measured directly with a previously described cell-type differential microcalorimeter. In addition to NaCl and NaBr, most of the homologous salts RNH3Br were studied from R = methyl to R = n-octyl. The results of the two simple salts are in excellent agreement with the best literature values.The enthalpies of transfer at infinite dilution, ΔHtr0(H2O → D2O), are mainly a measure of the structural ion–solvent interactions and of the exchange reactionUp to R = n-propyl, the relative apparent molal enthalpies of transfer,, are negative, approximately zero forn-butyl and positive for the higher members. This gradual change in the excess enthalpies of transfer is interpreted in terms of the increasing importance of hydrophobic interactions between the cations. When association occurs through micelle formation (R = n-octyl), there is a rapid increase inwhich results from hydrophobic bonding.

ISSN:0008-4042    

DOI:10.1139/v71-579

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

The saponification rates (measured at 25 ° by a titrimetric method) of the unprotonated forms of the methyl esters of glycine, alanine, leucine, valine, and phenylalanine were compared with those of theN-methyl, theN-acetyl, and theN-acetyl,N-methylamino acid analogues.N-Acetylation slightly increased or decreased the rate butN-methylation caused a reduction by as much as a factor of ten, depending on the complexity of the side-chain. The esters of theN-acetyl,N-methylamino acids, which exist ascisandtransisomers, were saponified at rates intermediate between those of the esters of theN-acetylamino acids andN-methylamino acids. Activation parameters were obtained for the phenylalanine and leucine derivatives.N-Methylation resulted in an increase in ΔH≠and ΔS≠which was attributed in part to solvation effects. The hydrolysis of the cationic esters of glycine and alanine was still evident at pH11.0.N-Methylation had little effect on the rates of saponification of the charged forms.

ISSN:0008-4042    

DOI:10.1139/v71-580

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

Several alleged chromanone-2-carboxylic acids were reexamined. Some were found to have the assigned structures but others are in fact 2-coumaranonylacetic acids. Diagnostic proof was obtained by analysis of the n.m.r. spectra of the corresponding reduced substances. Useful correlations of the spectra with the structures of the keto acids are proposed.

ISSN:0008-4042    

DOI:10.1139/v71-581

出版商:NRC Research Press    

年代:1971

数据来源: NRC