摘要:

The electrochemical half-wave reduction potential (E1/2) of 33 electron acceptor molecules in dry methylene chloride has been measured by cyclic voltammetry (CV) at a mercury electrode. The differences inE1/2values for the reversible reduction to the corresponding anion radicals reflect the electronic influence of the substituent at different ring positions.The measurements of the half-wave reduction potentials provided a convenient method for determining the conducting energy levels of the electron relay molecules in condensed media. Repetitive potential cycle measurements provided information on the chemical stability and cyclability of the intermediate anion radicals formed during electron transport processes.

ISSN:0008-4042    

DOI:10.1139/v84-322

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A dynamic gas blending system was used to generate controlled vapour concentrations of amphetamine, cocaine, or heroin. An adsorption – thermal desorption – gas chromatographic procedure was developed and used to measure the output vapour concentrations. The vapour pressure of amphetamine at 20 °C was determined, and vapour pressures as a function of temperature have been measured for cocaine and heroin.

ISSN:0008-4042    

DOI:10.1139/v84-323

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The adsorption of the cationic dye rhodamine 6G by montmorillonite (Wyoming bentonite) and laponite (synthetic hectorite) was studied by visible and fluorescent spectroscopy and by X-ray diffraction methods. Adsorption of the dye takes place by the mechanism of cation exchange. X-ray data indicate that the adsorbed cationic dye is located in the interlayer spaces of both minerals. It was found that adsorption prevents the dimerization of the dye, and gives rise to red shifts of the principal absorption band of the dye. A study of the effect of varying concentration of dye or clay on the location and intensity of this band proved to be useful in determining the adsorption capacity of the clay. The observed spectral changes are linked to surface polarity and to clay flocculation. At concentrated suspensions of montmorillonite, an additional weak absorption shoulder is obtained at 470–490 nm, which may be attributed to aggregated dye molecules, probably trapped within the cavities of book-house structured flocs. Due to steric hindrance rhodamine 6G does not give π interactions with the oxygen plane of the silicate layer. Therefore the adsorption of the dye by expanding clay minerals does not give rise to metachromasy. Fluorescence of the adsorbed dye is reported: it is red shifted and quenched relative to aqueous solutions. The use of fluorescence spectra to determine the saturation point is described, and aging and ultrasonic effects on spectral features are presented and discussed.

ISSN:0008-4042    

DOI:10.1139/v84-324

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The dynamic structures of [p-(dialkylamino)benzylidene]malononitriles have been investigated by1H nmr, and the kinetic and thermodynamic parameters for the partial rotation of the malononitrile moiety were obtained and those of the dialkylamino group were estimated. The rate of rotation of the above rotors were found to be of the order of ~104 s−1and ~107 s−1, respectively.

ISSN:0008-4042    

DOI:10.1139/v84-325

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Contrary to general expectations, kinetic methylation of camphor, 9-bromocamphor, or 9,10-dibromocamphor produces the 3-exo-methyl derivative as the major product.

ISSN:0008-4042    

DOI:10.1139/v84-326

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The vapour phase thermolyses at 400 °C of threegem-dimethylated 2-cyclohexenones1,2, and3were studied to determine the effect of blocking the direct conversion of these substrates to aromatic systems. In all three reactions it is proposed the major pathway taken was enolization followed by elimination of methane to yield a substituted phenol. This elimination reaction proceeded more readily with2than with either1or3, and HMO calculations which are consistent with this order of reactivity are presented. A general mechanistic scheme is proposed to account for the products formed and it is necessary to include a [1,5] sigmatropic methyl shift to explain the formation of at least one product in each thermolysis.

ISSN:0008-4042    

DOI:10.1139/v84-327

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Insertion of a carbon atom into a methyl cyclohexene, leading in a single synthetic step to a bicyclo[3.2.1.02.7]octane by carbene addition to the double bond and carbene insertion into a methyl C—H bond, has been accomplished by treating the cyclohexene with carbon tetrabromide and methyllithium at low temperatures. This new bicycloannulation method has been employed in a total synthesis of ishwarane (1), the naturally occurring parent hydrocarbon of the ishwarane class of tetracyclic sesquiterpenes. Although this reaction was not successful with various possible precursors of ishwarone (2), this natural product was prepared in low yield by a two-step version of the carbon atom insertion bicycloannulation (CAIB) procedure involving addition of bromoform-derived dibromocarbene to the octalone (5) followed by treatment of the resulting dibromocyclopropane (56) with methyllithium. The same two-step sequence was also successful in the first synthesis of norishwarane (20), the hydrocarbon comprising the bare ring system of the ishwarane sesquiterpenoids. The Diels–Alder synthesis used in the preparation of the octalin precursor (18) of norishwarane could not be used for the terpenes themselves because of the lack of dienophilic reactivity of the required cyclohexenone (7). A regioselective Diels–Alder equivalent sequence was therefore developed, consisting of conjugate addition of lithium di(3-methyl-3-butenyl)cuprate (42) to 2,3,4-trimethylcyclohex-2-en-1-one (7), epoxidation, base-catalyzed cyclization of the resulting epoxide (47) to a mixture of primary and tertiary alcohols (50and49, respectively), and dehydration of49to give5. In the case of ishwarane, the octalin precursor (62) was synthesized by conjugate addition of lithium dimethylcuprate to octalone59, addition of methyl magnesium bromide to the resulting decalone (60) to give octalol61, and dehydration.

ISSN:0008-4042    

DOI:10.1139/v84-328

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Condensation ofleuco-5-hydroxyquinizarin with aldehydes under Marschalk conditions (sodium hydroxide – water) gives 2-alkyl-5-hydroxyquinizarins with high regioselectivity, while the 3-alkyl compounds are obtained under Lewis conditions (piperidinium acetate – isopropanol). Reaction of the quinone with nitronate anions in methanol yields 2-alkyl derivatives exclusively.

ISSN:0008-4042    

DOI:10.1139/v84-329

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A synthesis ofcis,anti,cis-4,4-dimethyltricyclo[6.3.0.026]undecan-3-one is described in which the key step is β-enolate rearrangement of 9,9-dimethyltricyclo[5.3.1.01.5]undecan-10-one proceeding with retention of configuration. The required [5.3.1.01.5] ketone was prepared in six steps from tricyclo[5.2.1.01.5]dec-8-ene. This sequence constitutes a new route to the tricyclo[6.3.0.02.6]undecane ring system characteristic of the hirsutane sesquiterpenes. The13C data for several tricyclic derivatives are reported.

ISSN:0008-4042    

DOI:10.1139/v84-330

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A stereospecific synthesis of (+)-aphidicol-15-ene is described. Pursuing a concept successfully applied to our total synthesis of stemarin and the stemodane diterpenoids, the C/D ring system was elaborated by functional group manipulation and rearrangement of a 6-hydroxybicyclo[2.2.2]octan-2-one system.

ISSN:0008-4042    

DOI:10.1139/v84-331

出版商:NRC Research Press    

年代:1984

数据来源: NRC