摘要:

Dialkyl 2-chloropentylphosphonates, C3H7CHClCH2P(O)(OR)2, and monoalkyl 2-chloropentylphosphonic acids, C3H7CHClCH2PO2H(OR), have been dehydrohalogenated by strong bases to the corresponding pentenylphosphonic compounds. In all cases the kinetically controlled product was shown to be theE-1-pentenylphosphonic derivative. The α,β-unsaturated products underwent base-catalysed isomerization to the thermodynamically controlledE-2-pentenylphosphonic systems, thus indicating that the PO3R2and PO3R−groups destabilize (relative to hydrogen) the adjacent olefinic bond. The hydrogen–deuterium isotope exchange was studied for the α,β- and β,γ-unsaturated products and the results obtained were in full agreement with the isomerization results.

ISSN:0008-4042    

DOI:10.1139/v88-250

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The phenyl group is shown as a useful probe in sensing the environment in the1H nuclear magnetic resonance conformational study of a variety of quaternary heteroaromatic carbapenem derivatives. The influence of the -SCH2- substituent in determining the site of quaternization in nitrogen-containing heteroaromatic compounds is demonstrated through the acidity measurements of these methylene protons.

ISSN:0008-4042    

DOI:10.1139/v88-251

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The association constants for the electron donor–acceptor (EDA) complexes formed between bothcis-stilbene (cS) andtrans-stilbene (tS) as donors and methylviologen (MV+2) as acceptor were determined in ethanol and micellar sodium dodecyl sulfate (SDS) solutions in the range of SDS concentration 0.05–0.1 M. The values obtained in micellar solutions were much higher than those in ethanol and were heavily dependent upon SDS concentration. This effect is due to an increase in the local concentration of the reactants in the micellar pseudophase. The tS fluorescence quenching by MV+2was also studied in the same solvent media. In ethanol, the Stern–Volmer plot was found to be linear, with quenching constant (KSV) similar to the association constant determined by the absorption method. In micellar solutions, although upward curvature of the Stern–Volmer plots was observed, a reaction scheme based on static quenching via ground state EDA complex is proposed, which explains the experimental results. Irradiation in the absorption band of the EDA complexes formed by tS or cS and MV+2was carried out in ethanol and SDS solutions, in the absence of oxygen. Onlycis–transisomerization of cS in SDS solution was observed, with a quantum yield value of Φcis = 0.012.

ISSN:0008-4042    

DOI:10.1139/v88-252

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The isomerization of diterpene epoxides on active neutral alumina has established the existence of new rearrangements of the diterpene skeleton. Methyl 8,14β-epoxysandarcopimarate leads to bicyclic diterpene compounds by a Grob fragmentation, to derivatives of cleistanthane by a 1,2 migration of the vinyl substituent, as well as to one cycloditerpene compound. The 7,8 (or 8,9) derivatives of methyl isopimarate lead essentially to hydroxyolefins formed by a bifunctional acid–base mechanism at the alumina surface. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v88-253

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The basic hydrolysis of diazepam and severalN-alkyl nitrazepam derivatives has been studied in the presence of reactive counterion micelles of cetyltrimethylammonium hydroxide (CTAOH) and vesicles of didodecyldimethylammonium hydroxide (DDAOH). In both surfactants, the rate of hydrolysis of all compounds was found to be dependent on the hydroxide concentration at constant surfactant concentration and this was interpreted as evidence for initial amide hydrolysis. The hydrolysis in CTAOH was inhibited by added salts in the order Br− < NO3− < SO42−. At concentrations above 3 mMsurfactant, the rate of hydrolysis of each compound was similar in CTAOH and in DDAOH. At lower concentrations of CTAOH, however, the rate of hydrolysis was significantly lower than that in DDAOH. On the basis of this evidence, it was concluded that the cmc of CTAOH was between 2–3 mM, which is in good agreement with the value of 1.8 mMobtained by Zana from conductivity measurements. For diazepam, a mechanistic change is indicated on transfer from water to either micelles or vesicles and since vesicles are considered good models of biological membranes, this suggests that conclusions concerning the bioavailability of diazepam should not be based on studies in water but rather on studies in either micelles or vesicles.

ISSN:0008-4042    

DOI:10.1139/v88-254

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The photochemistry of 1,3,3,4- and 1,3,4,4-tetramethylcyclobutene has been investigated in pentane solution with monochromatic far ultraviolet (185, 193, and 214 nm) light sources, as well as in methanol solution with 214-nm excitation. Photolysis of each of the two isomeric cyclobutene derivatives results in competitive electrocyclic ring opening (yielding mixtures of stereoisomeric dienes in each case), fragmentation to yield propyne and methyl-2-butene, and isomerization to the other cyclobutene isomer. Quantum yields for product formation with 185-nm excitation have been measured in each case by cyclooctene actinometry. The occurrence of the interconversion process is offered as evidence for the intermediacy of cyclopropyl carbenes in the photochemistry of simple cyclobutenes in solution. On the basis of the known chemistry of carbenes of this type, their intermediacy in cyclobutene photochemistry may account at least partially for the formation of the formal (2π + 2π) cycloreversion products from photolysis of simple cyclobutene derivatives.

ISSN:0008-4042    

DOI:10.1139/v88-255

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Quadricyclane (1) and 1,8-bishoniocubane (2) have been found to undergo valence isomerization to norborndiene and tricyclo[4.2.2.02,5]deca-3,7-diene, respectively, on illuminated CdS and ZnO. An electron transfer mechanism is proposed. Quantum yield, solvent effects, the role of oxygen, and the quenching of the reaction were investigated, and were consistent with this interpretation. The thermal reaction of1on CdS was also suggested to be an electron transfer process involving, in this case, defects or trapped holes on the surface of the semiconductor. An examination of a series of strained hydrocarbons structurally related to1(tetracyclo[3.3.0.02,8.04,6]octane3, pentacyclo[4.3.0.02,4.03.805,7]nonane4and pentacyclo[4.4.0.02,4.03,8.05,7]decane5) resulted, largely, in a demonstration of the resistance of their respective radical cations to rearrangement prior to back electron transfer. Calculations by MNDO, in combination with a modified version of MM2, were used to explore the differences in the reactivity of the radical cations of1,3,4,5, and an interpretation is presented.

ISSN:0008-4042    

DOI:10.1139/v88-256

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

In-situFTIR spectroelectrochemistry has been applied to determine difference spectra in the region 1800 to 1000 cm−1associated with the oxidation of TPPH2, TPPMg, TPPCu, TPPZn, TPPCo, TPPMnCl, and TPPFeCl. In all cases, formation of the π-cation radical results in two characteristic absorbance decreases near 1600 and 1485 cm−1, and five characteristic absorbance increases near 1415, 1350, 1285, 1225, and 1005 cm−1. Formation of the π-dication was observed for TPPZn, TPPMg, and TPPCo, and gave rise to a new absorbance increase near 1600 cm−1, and a shift to higher frequency of bands in the 1200 to 1400 cm−1region. Perchlorate coordination to oxidized TPPZn, TPPMg, and TPPCo gives rise to bands near 1140 and 1030 cm−1.

ISSN:0008-4042    

DOI:10.1139/v88-257

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A study, by vapor phase chromatography, of the adsorption isotherms of benzene on raw and modified asbestos fibers as well as on fibers proposed as substitutes for asbestos shows that there is a marked difference in the behaviour of the various fibers examined. A comparison of the adsorbing power of raw and phosphorylated asbestos fibers, as well as asbestos fibers heated to 700 °C, has been made regarding their behaviour toward solutes bearing various functional groups, and it has shown the existence of physical adsorption as well as chemisorption. The presence of hydroxyl groups in the surface of the asbestos fibers favors the adsorption of organic molecules through hydrogen bonding. [Journal translation]

ISSN:0008-4042    

DOI:10.1139/v88-258

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The structure of the major product of the reaction of 1,2-dideoxy-3,4:5,6-di-O-isopropylidene-1-C-nitro-D-arabino-hex-1-enitol with 30% hydrogen peroxide and aqueous sodium hydrogencarbonate has been confirmed by X-ray crystallography to be that of 1,2-anhydro-3,4:5,6-di-O-isopropylidene-1-C-nitro-D-mannitol (2). The crystal structure of2, C12H19NO7, is orthorhombic,P212121, with cell dimensionsa = 10.269(3),b = 15.115(7),c = 9.295(8) Å, andZ = 4. The calculated density isDx = 1.336 gcm−3. The structure was solved by direct methods and refined to a residualR = 0.052. The molecule has a2G−conformation having bond lengths and angles in agreement with those observed in related structures, except for the C(1)—C(2), C(2)—C(3), and O(2N)—N bond distances which were found to be unusually small.

ISSN:0008-4042    

DOI:10.1139/v88-259

出版商:NRC Research Press    

年代:1988

数据来源: NRC