摘要:

The hydrolysis of 2-methoxy-2,3-dihydropyran shows a normal isotope effect (kH/kD > 1) under catalysis by the hydrogen ion and gives an accurately linear dependence of reaction rate upon undissociated acid concentration in cyanoacetic acid and formic acid buffer solutions. This substrate, therefore, unlike its higher homolog, 9-methoxyoxacyclonon-2-ene, provides no evidence in support of an anything but a normal mechanism for vinyl ether hydrolysis. Analysis of the hydrogen isotope effect suggests that a minor amount (8%) of this hydrolysis occurs via reaction of the acetal functional group.

ISSN:0008-4042    

DOI:10.1139/v80-353

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The highly congested molecule, methyl β,β-di-tert-butyl vinyl ether, undergoes reaction in dilute aqueous mineral acid solutions by a normal vinyl ether hydrolysis mechanism and gives an unrearranged aldehyde product. Thetert-butyl groups retard the rate of hydrolysis, but the effect ofcisandtranssubstituents is not cumulative; this is attributed to a repulsive nonbonded interaction, relieved in the course of reaction, between the ether oxygen atom and thecis-tert-butyl group buttressed by thetrans-tert-butyl group.

ISSN:0008-4042    

DOI:10.1139/v80-354

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Synthetic and chromatographic studies are presented on the Nash and Sawicki colorimetric methods for quantitating formaldehyde. It is shown that the actual color-forming agent in the Nash method is an isolable iminodione formedinsituby reaction of the two components. Explanation is given for differences between these two methods.

ISSN:0008-4042    

DOI:10.1139/v80-355

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The gear effect has been discovered and studied for the first time on molecules where the interacting groups were alkyl substituents. In order to be closer to biochemical models, this effect has now been studied where one interacting group is asymmetric and functional. For this purpose eighteen new compounds derived from alanine have been prepared and studied by nmr and dynamic nmr. The gear effect is operating, and it appears to be a suitable means to modulate the interaction of two active functions.

ISSN:0008-4042    

DOI:10.1139/v80-356

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Reactive hot-pressing experiments at 60–70 kbar and 700–900 °C indicate that the relative stability of the pyrochlore and weberite phases of the A2Sb2O7(A = Ca, Sr, Cd) antimonates depends primarily on the effective size of A2+and the covalency of the A—O bond working in conjunction. The analogous bismuthate(V) Sr2Bi2O7, obtained by hot pressing of SrBiO3−xwith an excess of KClO3, has been shown to have the weberite-type structure.

ISSN:0008-4042    

DOI:10.1139/v80-357

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The diffusion coefficient of SO2and acetonitrile in Nafion perfluorinated ion exchange membranes have been determined from chromatographic measurements of SO2concentration and the isotopic ratios in acetonitrile solutions. The diffusion coefficients vary with residual water content and attain values about one fifth those reported for water-saturated membranes falling in the range 1–2 × 10−7 cm2s−1. Values obtained for Teflon reinforced material indicates diffusion takes place over an effective surface more than twice the optically open area.

ISSN:0008-4042    

DOI:10.1139/v80-358

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The dual fluorescence observed in aqueous solution ofo-phenyl-phenol is attributed to a deprotonation equilibrium in the excited singlet state. The effect of oxygen on the primary photochemical process of formation of phenoxy radicals can be explained in a parallel study of the variations of fluorescence and photo-oxidation quantum yields of this phenolic compound at different pH. It is shown that photoionisation occurs only from the excited singlet state of the phenolate form. Oxygen inhibits recombination of the solvated electron and phenoxy radical. Increase of quantum yield for the disappearance of irradiatedo-phenyl-phenol in degased solution also is observed in the presence of electron scavengers like Cd2+or NO3−ions. Even when the phenoxy radicals are not able to react with oxygen, quantum yield for the disappearance of the phenolic compounds is higher in an aerated than in a degassed solution; the oxygen effect on the primary photochemical step may explain this difference.

ISSN:0008-4042    

DOI:10.1139/v80-359

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The aim of this paper is to present a minimal theory of thermal unimolecular reactions, including explicitly the kinetics of intramolecular randomisation processes. A quasi-diatomic model is formulated and, within the framework of the model, both first-and second-order randomisation processes among reactant and product states are examined.It is concluded that a vital mechanism for the intramolecular energy randomisation in thermal unimolecular reactions is a collisional one. On this assumption, a straightforward derivation of the Polanyi–Wigner specific rate function, as we have reinterpreted it, becomes possible.At the same time, anomalies in the fall-off curves for the thermal isomerisations of methyl isocyanide and ethyl isocyanide can be accounted for very simply: in the former case, values for both the first- and second-order randomisation rate constants can be derived, but in the latter case it is only possible to establish a lower limit for the second-order randomisation rate constant.

ISSN:0008-4042    

DOI:10.1139/v80-360

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The spin–lattice relaxation time has been measured at 33 MHz as a function of temperature for the liquid crystal MBBA and mixtures with carbon tetrachloride. The behaviour ofT1, close to the nematic–isotropic transition can be explained if the correct order fluctuation dependence is included. Diffusion constants calculated from fits to the self-diffusion contribution to relaxation are in agreement with existing results.

ISSN:0008-4042    

DOI:10.1139/v80-361

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The sorption of ammine complex cations of Co(III), viz. [Co(NH3)6]3+and [Co(en)3]3+, on the H+form of chromium ferrocyanide gel has been studied under static conditions. It is observed that the majority of these complex cations (90%) are sorbed by ion-exchange process. The extent of desorption of these complex ions with some uni- and bivalent cations is in the order K+ > NH4+ > Ba2+ > Sr2+ > Ca2+ > Mg2+.Infrared, Mössbauer, and magnetic susceptibility studies on the air-dried and powdered gel in H+form and loaded with [Co(NH3)6]3+, [Co(en)3]3+, Fe3+, and La3+ions show that prussiate compounds are not formed during the gel formation and the sorbed cations are held by the electrostatic attraction forces in the matrix, which is strained by the sorption of the big cations.

ISSN:0008-4042    

DOI:10.1139/v80-362

出版商:NRC Research Press    

年代:1980

数据来源: NRC