摘要:

The long-range spin–spin coupling constants between methylene protons and ring protons are measured in 3,5-dichlorobenzylamine, 3,5-dichlorobenzyldimethylamine, and in 3,5-dichlorobenzyldimethylarsine. The couplings over six bonds are used to derive internal barriers to rotation about the carbon–carbon bond to the phenyl ring. In the above order, they are 0.3 ± 0.3, 0.8 ± 0.2, and 3.0 ± 0.5 kcal/mol. The conformation of lowest energy in the arsine is that in which the CH2—X bond lies in a plane perpendicular to the benzene plane.

ISSN:0008-4042    

DOI:10.1139/v78-366

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A full analysis of the proton magnetic resonance spectra of 3-fluorotoluene and of 2-chloro-5-fluorotoluene, as 10 mol% solutions in CS2, demonstrates that the long-range spin–spin coupling constant over five bonds between methyl protons and fluorine-19 is negative. The coupling mechanism consists of a large positive σ electron component and a negative π electron component. The negative sign of the π electron contribution arises from a spin density in the 2pzorbital at carbon-3, which is opposite in sign to that of the spin densities at C-2 and C-4. Combined with positive hyperfine interaction constants,QCCHandQCF, the consequence is a negative π electron component.

ISSN:0008-4042    

DOI:10.1139/v78-367

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The assignments of the hydroxyl, hydroperoxyl, and alkylperoxyl radical spin adducts of α-phenylN-tert-butyl nitrone (PBN) are discussed. Results of new experiments designed to test the assignments of the first two are described. It is concluded that the hydroxy adduct assignment is correct. The relationship betweenaβHandaNisThis equation gives a good fit for the seven pairs of constants reported for the hydroxy adduct. The assignments for the hydroperoxy adduct may be correct but no proof is yet available for this assignment.

ISSN:0008-4042    

DOI:10.1139/v78-368

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Proton magnetic resonance bas been used to investigate the double stranded RNA helix GAGC:GCUC, whose sequence corresponds to the duplex neck region of several tRNAs, a possible aminoacyl-tRNA synthetase recognition site. The nonexchangeable base and ribose anomeric resonances of the separate tetranucleotides were characterized by linear and predominantly upfield chemical shift changes as the temperature was decreased from 65 to 15 °C. When these strands were mixed nonlinear, sigmoidal shift changes consistent with base pairing were observed. The melting temperature of the duplex was determined to be 42 ± 1 °C which was in excellent agreement with the value obtained from optical methods. This is the first1Hmr study of a non-self-complementary duplex prepared from synthetic tetraribonucleotides.

ISSN:0008-4042    

DOI:10.1139/v78-369

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Proton nuclear magnetic resonance was used to examine double helix formation in the self-complementary oligoribonucleotide CAUG in neutral D2O containing 1.0 MNaCl. Using the procedure of incremental assignment all the nonexchangeable base and ribose anomeric protons could be assigned and were observed over the temperature range of 70 to 4 °C. The chemical shift changes that occurred over this temperature range were sigmoidal in nature which is indicative of base-pairing. From the plot of chemical shift vs. temperature aTmof 24 ± 1 °C was determined. This is the first nmr study of a duplex formed from tetranucleotides which contains two internal A•U base pairs.

ISSN:0008-4042    

DOI:10.1139/v78-370

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The reactions of IOF5with SbF5and with AsF5have been investigated at low temperature by19F nmr and Raman spectroscopy. It was found that SbF5forms labile 1:1 and 2:1 complexes whereas AsF5forms only a 1:1 complex. The IOF5is bound through its oxygen atom to the Lewis acids AsF5, SbF5, or (SbF5)2.

ISSN:0008-4042    

DOI:10.1139/v78-371

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The nature of the interactions between unsaturated hydrocarbons and dipolar aprotic solvents, which occur in the extractive distillations, has been studied by13C nmr, dielectric constant, and dipole moment measurements. The results of these different methods are in agreement with dipolar interactions.

ISSN:0008-4042    

DOI:10.1139/v78-372

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The electrochemical oxidation of titanium metal in the presence of an essentially non-aqueous electrolyte phase yields titanium(III) species in solution. It has been shown that this method of generating TiX3(X = balancing anion) forms the basis of a convenient way of reducinginsitucertain organic functional groups (sulfoxide, oxime, haloketone, vinyl dicarboxylic acid, and nitro aromatics). The stoichiometry of the reaction has been established in each case, and corresponds to the oxidation of TiX3and the formation of the appropriate organic compound. The yields are comparable to those reported in experiments using aqueous titanous chloride.

ISSN:0008-4042    

DOI:10.1139/v78-373

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

It has been demonstrated that the addition of N2, CO, Ne, Ar, Kr, Xe, CO2, and CF4to a H2-air diffusion flame containing He and traces of CH4enhances the level of ion formation. This enhancement is proportional to the concentration of both CH4and the diluent gas, consistent with the proposition that the diluent gas participates in the ion formation process.

ISSN:0008-4042    

DOI:10.1139/v78-374

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Ion formation from traces of C2N2in a H2 + He-in-air diffusion flame is enhanced by the presence of traces of Ne, Ar, Kr, Xe, N2, CO, CO2and CF4. The enhancement is proportional to the concentration of both C2N2and the diluent gas and the relative efficiencies are identical to those observed when hydrocarbons are the source of ionization. The observations are consistent with the involvement of the diluent in ion formation, parallel to the hydrocarbon system.

ISSN:0008-4042    

DOI:10.1139/v78-375

出版商:NRC Research Press    

年代:1978

数据来源: NRC