摘要:

Voltage transients under galvanostatic conditions are investigated for the system Al/Al2O3/electrolyte (glycol–borate) and the results, along with similar results obtained by Dewald for the system Ta/Ta2O5/electrolyte (0.1 NH2SO4), are analyzed according to the dielectric relaxation model due to Dignam. This model accounts for the general form of the transients, but systematic discrepancies are apparent. Modification of the model to include two independent ion-current-driven dielectric relaxation processes gives essentially exact agreement with the data and values for the constants in accord with those obtained earlier from potentiostatic transient measurements.

ISSN:0008-4042    

DOI:10.1139/v72-521

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Experiments are described in which the a.c. impedance of the system Al/Al2O3/electrolyte (glycol–borate) is measured under conditions of steady-state film growth. Using an equivalent circuit of a resistive and capacitive element in parallel, the results are presented in the form of the a.c. conductance, σac, and effective dielectric constant,Keff, of the oxide film as a function of the d.c. current density,I0, and angular frequency ω. The results show that σac/I0andKeffvary with (ω/I0), but within experimental error are independent of ω andI0separately. The dielectric relaxation model, assuming two ion-current-driven relaxation processes and using the constants determined in Part I, reproduces the data almost within experimental scatter. A poorer fit is achieved if only one relaxation process is assumed.

ISSN:0008-4042    

DOI:10.1139/v72-522

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

A total synthesis of cadin-4,10(15)diene-3α-ol, one of the structures proposed for khusinol, is described. Neither this compound nor its C3-epimer was identical with khusinol.

ISSN:0008-4042    

DOI:10.1139/v72-523

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The synthesis of 8,3′-thioanhydroguanosine is described. The anhydro ring is formed by displacement of bromine from position-8 and methanesulfonate from the 3′-position using thiourea in refluxingn-butanol. The 8,3′-thioanhydroguanosine is converted by Raney nickel reduction to 3′-deoxyguanosine, an analogue of cordycepin.

ISSN:0008-4042    

DOI:10.1139/v72-524

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Nine known serratane triterpenoids have been isolated fromLycopodiumlucidulumMichx. mostly as their acetates. Serratenediol is the major one and is accompanied by significant amounts of serratriol. Moderate quantities of serratenediol-3-acetate, tohogenol, and episerratenediol were present together with minor amounts of 16-oxoserratriol, tohogeninol, and the phlegmanols A and E.

ISSN:0008-4042    

DOI:10.1139/v72-525

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Values of the Hammett acidity functionH0can be correlated for strong acid solutions up to −H0values of 3.5 via a Bascombe and Bell type equation:taking into account the degree of dissociation of the acids. This can be interpreted according toandAlternatively, an approach based on the treatment of equilibrium constants in terms of mole-fractions yieldsvalid for the same acids (H2SO4, HClO4, HCl, and HNO3) and again involving a tri-dehydration of the tetra-hydrated proton. The log of the ratiohas been found to be proportional to −H0itself and to be otherwise independent of the nature of the acid anion.

ISSN:0008-4042    

DOI:10.1139/v72-526

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

A study of the pyrolysis of a series of neopentyl-type xanthate esters was carried out at 250 °C. The formation of olefins and dithiolcarbonates were found to be two competing processes. The olefin formation process became more important when the number of β-phenyl groups increased and when there was an electron donating group substituted at the para-position of the β-phenyl ring. Kinetics studies supported the proposal that the transition state of the olefin formation process involved a stabilized phenonium ion. However the dithiolcarbonate formation became more important when there was the least number of β-phenyl substituents and this rearrangement appeared to proceed through a concerted four-membered cyclic transition state.

ISSN:0008-4042    

DOI:10.1139/v72-527

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

Fluorescent yields ofexcited in the 2500 Å region in cyclohexane solution have been examined. There is a general trend of fluorescent yields decreasing with increasing alkene ring size. The sum of the fluorescent and triplet yields decreases with increasing ring size. Triplet energies, obtained by Evans' method and roughly confirmed by phosphorescent emission spectra at 77 °K, do not vary greatly.

ISSN:0008-4042    

DOI:10.1139/v72-528

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

The effect of 2,4,6-tri-t-butylphenol on the rate of polymerization of vinyl acetate and on the degree of polymerization of the resultant polymer has been determined. It is shown that the phenoxy radicals produced by hydrogen transfer do not reinitiate polymerization and that they disappear from solution by reaction with polyvinyl acetate radicals. The chain transfer constant is estimated to be 0.017 ± 0.004 at 45° from molecular weight studies and 0.021 ± 0.004 from rate studies. Stationary state concentrations of phenoxyl of the order of 10−7 Mhave been determined by e.s.r. spectroscopy. The rate constant for the reaction of polyvinyl acetate radicals with 2,4,6-tri-t-butylphenoxyl is (6.6 ± 2.3) × 107 l mol−1s−1at 45°.

ISSN:0008-4042    

DOI:10.1139/v72-529

出版商:NRC Research Press    

年代:1972

数据来源: NRC

摘要:

An investigation of the precursor activity of α-bisabolol, γ-bisabolene and monocyclofarnesol indicates that these compounds are not intermediates in the biosynthesis of trichothecin.

ISSN:0008-4042    

DOI:10.1139/v72-530

出版商:NRC Research Press    

年代:1972

数据来源: NRC