摘要:

When cyclobutane (1) is shaken at 0 °C with [3H]CF3SO3H (2-t) or with (2H)CF3SO3H (2-d), incorporation of T or D into the hydrocarbon layer readily occurred. All eight H atoms of1can be involved in the exchange since polydeuterated species including octadeuterated hydrocarbons were observed by mass spectrometry. In an experiment with1and2-t, quenching of the acid layer with H2O gave a mixture of cyclobutanol, cyclopropylcarbinol, and allylcarbinol in the ratio of 61:37:2, respectively, as estimated by isotopic dilution, while vpc analysis of the hydrocarbon layer showed the presence of1, methylcyclopropane, and 1-butene in the ratio of 66:30:4. The results are explained by a carbocationic chain mechanism, involving the formation of equilibrating bicyclobutonium ions. Similar but slower incorporation of T into the hydrocarbon layer was observed when1was treated with [3H]H2SO4.

ISSN:0008-4042    

DOI:10.1139/v80-001

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The photochemistry of di-tert-butylselenoketone1and selenofenchone2has been examined. Their photochemical properties resemble those of thioketones rather than ketones in that hydrogen abstraction occurs from an upper excited state and not from the lowest (n → π*) excited state. Di-tert-butylselenoketone,1, on irradiation into theS2band forms the diselenide3. The quantum yield for this process was found to be 0.0055 and was increased in the presence of a good hydrogen atom donor. No reaction was observed following excitation into theS1state unless a good hydrogen atom donor was present, and even then the photoreaction was very inefficient. Quenching experiments with biacetyl demonstrated the lifetime of the abstracting state to be in the order of 10−11 s. The formation of the diselenide3has been rationalized in terms of hydrogen abstraction from solvent by photoexcited1and trapping of the radicals produced by ground state1, leading to the radical6. The mechanism is supported by esr evidence for the existence of6. Selenofenchone,2, also, did not react following excitation into theS1state, but underwent intramolecular cyclization in a similar manner to bicyclic thioketones following excitation into theS2state.

ISSN:0008-4042    

DOI:10.1139/v80-002

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The reaction of Li metal with alkyldiphenylphosphines generates the alkylphenylphosphide anions, which can undergo subsequent reactions with alkyl halides to give chiral phosphines (RR′R″P). The31P nmr chemical shifts have been measured for these phosphines, and show greater deviations from the values predicted by the first order additivity model than do those of more symmetrical phosphines (i.e., R3P and R2R′P). The shifts for these chiral molecules, and for a wide range of other phosphines, can be accurately predicted using a second order pairwise additivity scheme. The dependence of the observed and calculated chemical shifts upon electronegativity and steric factors is discussed.

ISSN:0008-4042    

DOI:10.1139/v80-003

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Electrical conductivity measurements are reported for solutions in trifluoromethanesulfonic acid of a number of simple and complex bases, including univalent and divalent metal trifluoromethanesulfonates. The univalent metal salts, water, aniline, and acetic acid behave as fully dissociated bases, while the alkaline earth metal salts show considerable ion association. The trifluoromethanesulfonate anion appears to have an abnormally high mobility, as compared to the metal cations, and is believed to conduct by a proton-transfer mechanism. Dissociation constants for some weak organic bases and association constants for strontium and barium trifluoromethanesulfonates are estimated. Sulfuric acid behaves as a weak electrolyte, while sulfur trioxide is effectively a non-electrolyte. The conductivities of potassium nitrate and potassium dihydrogenphosphate are consistent with the formation of the nitryl cation and the phosphate acidium ion, respectively.

ISSN:0008-4042    

DOI:10.1139/v80-004

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

This study of the anodic behavior of magnesium in simulated seawater has shown that the corrosion product formed at the surface of the electrode depends mainly on the nature of ions dissolved in the electrolyte. Analyses of the corrosion product, formed in the presence of a high concentration of chloride ions, are compatible with the formation of a compound having approximately the formula 5Mg(OH)2•MgCl2. However, this complex is gradually transformed over a period of several hours into Mg(OH)2.A model of the oxidation mechanism is presented in which the characteristics of the anodic behavior of magnesium are related to the structure of the oxidation layer. For example, the activation of the surface of the anode, the kinetics of the hydrogen evolution reaction, and the large difference between values of corrected and uncorrected electrode potential can all be explained by this model. It is the resistance of the film to the flow of current which controls the kinetics of anodic dissolution of magnesium.

ISSN:0008-4042    

DOI:10.1139/v80-005

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The epoxidation of allylic alkenes in the 6-tert-bulyl (or 6-trimethylsilyl or 6-trimethylgermyl) 3,3-dimethylcyclohexenes is examined; it has been found that the stereochemistry of these reactions is governed mostly by steric factors. The results obtained by the reduction ofcisandtransepoxides by lithium aluminium hydride are also reported, the regiochemistry and the stereochemistry of the reactions of reduction are governed by steric factors as well as by the electronic effects of the trimethylsilyl group.

ISSN:0008-4042    

DOI:10.1139/v80-006

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Proton magnetic resonance relaxation time studies at 200 and 400 MHz have been measured for vitamins D2, D3, as well as the biologically active 1α,25-(OH)2D3. A comparison of these relaxation times at the two frequencies allows the evaluation of the dipolar correlation times for the different protons in the molecule. These are very short, and range from < 0.7 × 10−10 s to 1.2 × 10−10 s. Application of the Solomon equation to the relaxation times of the 19Zand 19Eprotons allows a calculation of the internuclear distance since these two geminal protons relax each other predominantly by the dipolar mechanism. Using theT1values, the calculated distances are 1.98 ± 0.10 Å for 1α,25-(OH)2D3, 2.01 ± 0.10 Å for D3, and 1.95 ± 0.10 Å for D2. The calculated distance based on a neutron diffraction distance for the C—H bond is 1.91 Å. The measurement of the relaxation times also allows a definitive spectral assignment of the 21- and 28-methyl protons for vitamin D2.

ISSN:0008-4042    

DOI:10.1139/v80-007

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Cyclobutanones derived from α-phenyl, α,α-diphenyl, and bisphenyleneketene cycloaddition to dihydrofuran and dihydropyran were rearranged under acidic conditions to polycyclic aromatic dihydrofurans and dihydropyrans respectively. A mechanism for these rearrangements is proposed.

ISSN:0008-4042    

DOI:10.1139/v80-008

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

A kinetic study of the addition reactions of borohydride and sulfite ions and of hydroxylamine to a number of stereospecifically deuterated carbonyl compounds (3,3,5,5-tetramethyl cyclohexanone, 7,7-d2-bicyclo[2,2,1]-2-bornanone) leads to the observation of a distant secondary deuterium isotope effect. The results obtained reveal the intervention of a directional effect in the steric origin of these isotope effects. In particular, this study shows the importance of the orientation of the vibrations brought into play by a C—D bond during the reaction process. (Journal translation)

ISSN:0008-4042    

DOI:10.1139/v80-009

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

N-tert-Butyldimethylsilyl derivatives of imidazole, 2-methylimidazole, 4-methylimidazole, benzimidazole, pyrazole, 1,2,4-triazole, and benzotriazole were prepared fromtert-butyldimethylsilyl chloride and the corresponding heterocyclic compound. The products were identified by carbon and proton nmr, mass spectrometry, and elemental analysis. The carbon nmr spectra confirmed the absence of intermolecular silyl exchange at ambient temperature. Silyl exchange did occur at elevated temperatures, 130–160 °C.Reaction ofN-tert-butyldimethylsilyl orN-trimethylsilyl heterocycles with dimethylsulfoxide gaveN-(methylthio)methyl derivatives of imidazole, 2-methylimidazole, 4-methylimidazole, benzimidazole, pyrazole, and 1,2,4-triazole. The products were characterized by carbon and proton nmr, mass spectrometry, and elemental analysis. A mechanism involving a Pummerer rearrangement is proposed to account for the results.

ISSN:0008-4042    

DOI:10.1139/v80-010

出版商:NRC Research Press    

年代:1980

数据来源: NRC