摘要:

The kinetics of the hexagonal–cubic phase transformation of zinc sulfide have been studied invacuo, in zinc vapor, and in sulfur vapor in the temperature range 800–900 °C by a powder X-ray diffraction technique. The transformation rate is enhanced in the presence of sulfur and zinc vapor. Invacuoand in sulfur vapor the reaction is nucleation-controlled with activation energies of 95.0 and 98.5 ± 5 kcal, respectively. In zinc vapor the reaction is diffusion-controlled with the diffusion coefficient expressed asThe modes of catalytic action by sulfur and zinc vapor on the solid phase transformation reaction are discussed.

ISSN:0008-4042    

DOI:10.1139/v68-479

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The temperature dependence of the rates of neutral hydrolysis of a series of alkyl trifluoroacetates (CF3COOR; R = methyl, ethyl,s-propyl,t-butyl) has been determined in both light and heavy water. From these studies the thermodynamic parameters (ΔH≠, ΔS≠) which characterize the activation process have been calculated. Sufficient rate data have been obtained in the case of the ethyl ester to calculate the heat capacity of activation (ΔCP≠) for the hydrolysis of this compound in light water. Both the entropies and enthalpies of activation as well as the solvent isotope effects are consistent with the proposal that the primary and secondary esters react by an acyl–oxygen BAc2 mechanism, in contrast to the tertiary ester, which appears to react either by a carbonium ion (SN1) process or by a route which combines both the BAc2 and SN1 paths.

ISSN:0008-4042    

DOI:10.1139/v68-480

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The ordinary Hückel molecular orbital (H.m.o.) method and the linear combination of molecular orbitals (l.c.m.o.) method in a perturbational form have been used to calculate the π-electron energy levels appropriate to a series of 24 Schiff bases (S.b.'s) of the type ArCH=NAr′, where Ar— and Ar—′ are unsubstituted aryl groups. The energy levels calculated by both the H.m.o. and l.c.m.o. treatments are shown to give a satisfactory account of the polarographic data for the S.b.'s reported in Part I of the present series. However, the l.c.m.o. method appears to offer a deeper insight into the variation of the half-wave potentials for the first electron transfer with the structure of the S.b.

ISSN:0008-4042    

DOI:10.1139/v68-481

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

N-Cyanopiperidines (1and2) have been shown to possess a n → π* transition band in the vicinity of 260 mμ and, in the presence of a dilute acid, undergo photolytic reactions leading to hydration products (3and4). The fact that the reaction can be sensitized by acetophenone demonstrates that1reacts through a triplet state.ETis about 76 kcal/mole. Increasing the water content in the photolysis medium reduced the yield of the hydration product.

ISSN:0008-4042    

DOI:10.1139/v68-482

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

First-order rate constants for the decarboxylation of fourteen 4- and 5-substituted salicylic acids have been determined in quinoline solution in the temperature range 90–230 °C. Substituents have almost no effect on the rate constants, except those with large negative σ-constants:p-amino,p-hydroxy,p-ethoxy. The enthalpies and entropies of activation do not fit the isokinetic relationship, with the same three substituents deviating. It is suggested that the decarboxylation involves a preliminary ionization of the carboxyl group, followed by protonation of the aromatic ring of the anion so formed, and then loss of carbon dioxide. The isokinetic relationship fails because substituents affect all three steps differently, and the Hammett relationship fails because the substituent effect on the ionization is related to σ while that on the other two steps follows σ+. The three substituents which deviate are those for which σ and σ+differ widely.

ISSN:0008-4042    

DOI:10.1139/v68-483

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

Mass spectrometric methods and a Ge(Li) γ-ray detector have been used to obtain reactor-neutron (> 1 MeV) fission yields of232Th. The results have been combined with earlier mass spectrometric and radiochemical work.

ISSN:0008-4042    

DOI:10.1139/v68-484

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The infrared spectra of CH2FCH2OH were measured in the vapor, liquid, and solid states from 4000 to 200 cm−1. The Raman spectrum of the liquid was also measured over the same frequency range. From the results it appears that the free molecules exist almost entirely in thegaucheconfiguration, which is stabilized by intramolecular hydrogen bonding. Only in the vapor at temperatures above 60 to 70 °C is there any indication of weak bands due totransisomers. In the condensed phases the molecules are associated through strong hydrogen bonds (3–4 kcal/mole).

ISSN:0008-4042    

DOI:10.1139/v68-485

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The reaction between Hg(3P1) atoms and methyl mercaptan at 55° is mainly H-atom removal from sulfurwith a minor participation (~10%) of C—S bond ruptureEthyl mercaptan dissociates by two main processesSome evidence was found for a small amount of dissociation by C—C bond rupture. No C—H bond rupture in either compound could be detected.

ISSN:0008-4042    

DOI:10.1139/v68-486

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The rate coefficients for the reaction with diazodiphenylmethane in methanol, ethanol, isopropyl alcohol,t-butyl alcohol, 2-methoxyethanol, 2-n-butoxyethanol, dimethyl sulfoxide, ethyl acetate, and toluene at 30° and the pKavalues in water, 50% ethanol–water, and 80% 2-methoxyethanol–water of 18 substituted acetic and propionic acids have been determined. A further 14 acids have been studied to a more limited extent. The effect of substitution has been estimated by linear free energy relations. The reaction constants for the ionization reaction are almost independent of the medium. This is interpreted as being due to the field effect of the proximate polar substituents passing through the molecular cavity almost alone. The occurrence of steric inhibition of solvation causing acid weakening for bulky multi-substitution is confirmed. The reaction constants for the esterification reaction are affected by the solvent. This is attributed to dependence on solvation of the transition state.

ISSN:0008-4042    

DOI:10.1139/v68-487

出版商:NRC Research Press    

年代:1968

数据来源: NRC

摘要:

The pKavalues of a series of ortho-substituted benzoic acids in 50% ethanol–water have been determined. The effect of ortho-substitution on the ionization of benzoic acid in this and other solvents has been correlated by a linear free energy relation. The reaction constants found are compared with those for the meta/para-substituted benzoic acids. While those for the former system are insensitive to changes in the medium, the latter vary considerably. It is suggested that this is due to transmission by the field effect passing almost entirely through the molecular cavity for ortho-substituents.

ISSN:0008-4042    

DOI:10.1139/v68-488

出版商:NRC Research Press    

年代:1968

数据来源: NRC