摘要:

Thecation, where chiraphos is 2,3-bis(diphenylphosphino)butane, has been synthesized and fully characterized by spectroscopy and single crystal data on the chloride salt (1). Crystals are monoclinic,a = 23.106(3),b = 12.4987(8),c = 21.455(3) Å, β = 128.539(5)°,Z = 4, space groupC2. The structure was solved by conventional heavy atom methods and was refined by full-matrix least-squares procedures toR = 0.046 andRw = 0.032 for 4509 reflections withI > σ(I). The coordination about Rh is square planar distorted toward tetrahedral within the five-membered chelate rings, similar to that in, where dpe is 1,2-bis(diphenylphosphino)ethane, but the distortion toward tetrahedral is significantly greater in1; the methyl substituents further restrict rotational freedom about the P—Ph bonds, which leads to some blocking of the axial ligand sites by the four H atoms of the chelate-ring carbon atoms. In solution,1is unreactive towards O2, CO, and H2, but oxidatively adds HX (X = Cl, Br) to givetrans-species.

ISSN:0008-4042    

DOI:10.1139/v86-011

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Energetic positive muons thermalizing in alkane vapors are observed in either diamagnetic environments, with relative fractionfD, or as the polarized muonium atom (Mu = μ+e−), with fractionfMu. The fractionfDis found to vary from ~0.12 in CH4to ~0.24 in n-C6H14at pressures near 1 atm (300 K); some pressure dependence in yield is also observed, notably for the heavier alkanes. The diamagnetic fraction (yield) is interpreted as due to hot atom reactions (Mu*) incomplete analogy with past studies in hot tritium (T*) chemistry. The data have been interpreted within the Wolfgang–Estrup formalism and compared with similar analyses of T* reactions for (unmoderated) alkane systems. It is concluded that the energy loss parameter (α) is determined largely by inelastic scattering effects. If these are assumed to be the same for both Mu* and T* moderation, then the resulting reactivity integrals (I) for the noncyclic alkanes are found to exhibit the same trend with mass as in hot tritium chemistry, giving, on average, ~6:1 for the ratioI(T*)/I(Mu*).

ISSN:0008-4042    

DOI:10.1139/v86-012

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The one- and two-electron reductions of 2-thioriboflavin withand cyclic disulphide anion of dithiothreitolhave been studied by the steady state γ and pulse radiolysis techniques. Theradical reacted with 2-thioriboflavin to give the neutral semiquinone (•FlH) and the radical anion (•Fl−) at pH 5 and 10 respectively. The pKof the •FlH radical was determined to be 7.4. In the case of the anion, the 2-thioriboflavin spectrum is similar in shape to that of FAD radical anion, but red shifted by 40–50 nm. Red shifts are also seen in the neutral •FlH form for the 370-nm peak and 580-nm shoulder. However, in addition, there is strong enhancement of the absorbance at 500 nm. The spectrum of 2-thioriboflavin semiquinone produced in the presence of 2–5 mMdithiothreitol was perturbed, as was observed previously for unsubstituted flavin semiquinones in the presence of sulphydryls. The rate constants for the initial one-electron reduction step viz:were 4.0 ± 0.5 × 109 M−1 s−1and 1.3 ± 0.2 × 109 M−1 s−1at pH 7 and 10 respectively. The corresponding rate for the reaction ofwith 2-thioriboflavin at pH 7 was determined to be 2.4 ± 0.2 × 109 M−1 s−l. The continuous production ofradicals by γ radiolysis reduced 2-thioriboflavin to the dihydro form, and the flavin was regenerated on the addition of air. Theradical also effected a two-electron reduction. However, in this case, if the process was taken beyond the equivalence point, the dihydroflavin spectrum was bleached and the oxidized flavin could not be recovered.

ISSN:0008-4042    

DOI:10.1139/v86-013

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The paramagnetic1H nmr spectra for manganocene (1) and 1.1′-dimethylmanganocene (2), and the13C nmr spectra for 1,1′-diethylmanganocene (3) have been recorded in toluene solvent over a −90 to 90 °C temperature range.1shows a low field and a high field ring proton resonance in its spectrum near −59 °C. At higher temperatures the low field resonance is prevalent and becomes gradually averaged due to a fast spin exchange process that dominates the spectrum at 90 °C. For the ring substituted derivatives2and3, resonances due to only one paramagnetic species were detected in the low temperature range. Above ambient temperature a new spectrum due to rapid spin exchange averaging is observed for these complexes. Results are readily interpreted in terms of ground state molecular cross-over exchanges between the2E2g,6A1g, and2A1gspin states of the complexes.

ISSN:0008-4042    

DOI:10.1139/v86-014

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The electrochemical oxidation of aromatic heterocyclic compounds thiophene, pyrrole, and indole and benzenoid and nonbenzenoid polycyclic hydrocarbons azulene, fluorene, and pyrene yield electrically conducting polymers with conductivities of 10−5–10 S/cm. The presence of substituents affects the electrical conductivity of these films and also their electroactive properties. Furthermore, substituents determine whether electropolymerization of these compounds can occur or whether soluble products are formed. The relative importance of these pathways is dependent on the stability of the intermediate radical cation. These effects are investigated by INDO molecular orbital calculations.

ISSN:0008-4042    

DOI:10.1139/v86-015

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

An intrinsic selectivity is defined for identity SN2 reactions (X− + RX → XR + X−). This selectivity parameter is shown to yield information about: (a) the average looseness of the TS geometry in a reaction series; and (b) the sensitivity of the reaction series to geometric loosening.

ISSN:0008-4042    

DOI:10.1139/v86-016

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The effects of multiple substitution by methoxy and cyano in the 4-position(s) of 1,1,2,2-tetraphenylcyclopropane (1) and 1,1,3,3-tetraphenylpropenyl radical (2•) on the oxidation potentials have been measured. The results indicate that the oxidation process for the cyclopropanes (1a–m) is irreversible. Nevertheless, the substituent effect on the potential is essentially additive and correlates reasonably well with Σσ+. A slow electron transfer process (an overall conversion of1to2+), with a transition state resembling the ring-opened radical cation, is consistent with these observations. The oxidation of the radical2•is quasi-reversible in dichloromethane. In this case also, the substituent effect on the oxidation potential is additive and correlates with Σσ+. Any deviation from planarity of2•is not sufficient to prevent substituents from exerting normal (additive) behaviour.

ISSN:0008-4042    

DOI:10.1139/v86-017

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A systematic study of reductions of unsymmetrically substituted maleic anhydrides by a variety of metal hydride reagents indicates that the high regioselectivity observed in these reactions is controlled chiefly by electronic factors.

ISSN:0008-4042    

DOI:10.1139/v86-018

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The total synthesis of the position-17 sulfur analogs of the perchlorate salts of the morphinans, (±)-levorphanol and (±)-isolevorphanol via4a-(2-aminoethyl)-1,2,3,4,4a,9-hexahydro-6-methoxyphenanthrene, a key intermediate in the synthesis of butorphanol (4), is described. 2D-Correlation and heterocorrelation nuclear magnetic resonance spectroscopy confirmed the configurational relationship of the isosteres.

ISSN:0008-4042    

DOI:10.1139/v86-019

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Interfering effects of different cations on the atomic absorption signal of platinum can be completely eliminated by addingn-butylamine. The releasing action ofn-butylamine comes through the formation of a volatile, platinum–amine complex, so the platinum species reaching the flame will normally be independent of the original composition of the solution. The inhibition release titration method has been used in studying the interfering effects to achieve a determinate characterization of compound formation.

ISSN:0008-4042    

DOI:10.1139/v86-020

出版商:NRC Research Press    

年代:1986

数据来源: NRC