摘要:

AbstractThe reactions of 1‐p‐methoxyphenyl‐2‐methylpropen‐1‐yl trifluoroacetate (I–OCOCF3) and 3,5‐dinitrobenzoate (I–ODNB) in AcOH/NaOAc or with amines in 2,2,2‐trifluoroethanol (TFE) were investigated. In TFE, I–ODNB gives trifluoroethyl 3,5‐dinitrobenzoate (II) and the ketone AnCOCHMe2(III) in a second order reaction with five amines and with CF3CH2ONa, and I–OCOCF3gives a second order reaction with 2,6‐lutidine. In AcOH/NaOAc, I–OCOCF3gives the corresponding acetate I–OAc, and I–ODNB gives I–OAc and III. The kAcOH/kAcODvalues are 5.5–6.2 for I–OCOCF, and 1.03 ± 0.05 for I–ODNB. It is suggested that the rate determining step in TFE is the attack of CF3CH2O−(formed from the amine and TFE) on the carbonyl of the ester group in a BAC2 mechanism. In AcOH, an electrophilic addition‐elimination mechanism (AdE–E) for the reaction of I–OCOCF3is supported by the solvent isotope effect. The solvent isotope effect and the products from I–ODNB in AcOH are consistent with an SN1 mechanism, but since the kCl/kODNBratio is lower than that in saturated systems, an AAC2 mechanism cannot be unequivocally excluded. The effect of the le

ISSN:0021-2148    

DOI:10.1002/ijch.197400094

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe reduction of nitroalkanes at the dropping mercury electrode in neutral solutions (pH 5.4–7.4) was studied. Careful measurements at the foot of the polarographic wave allow accurate determination of the Tafel slopes to within ± 1 mV, thus the effect of molecular size on the Tafel slope could be determined. The analysis of the results indicates that the adsorbed intermediate, which is a charged species, is situated about halfway between the metal surface and the outer Helmholtz plane. It is also shown that the intermediate is adsorbed with the functional nitro group lying flat on the surface. Only the carbon atoms in the position α and β to the nitrogen atom seem to occupy space on the surface. The importance of employing several members of a homologous series having a common functional group to evaluate the mechanism of electrode reactions is emphasized and the importance of employing the combined isotherm in such analysis is pointed

ISSN:0021-2148    

DOI:10.1002/ijch.197400095

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe laser Raman spectra of halogen nitrates were recorded and polarization measurements performed. Out of the nine expected fundamentals, eight were observed and the ninth deduced from its overtone. From the number of depolarised lines and their width, it was concluded that these molecules are of a non‐planar structure of C1vsymmetr

ISSN:0021-2148    

DOI:10.1002/ijch.197400096

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe design of a thermostat which gives a temperature stability of ± 1.5 × 10−4°C over a period of weeks is described. The temperature sensors are thermistors stabilized by heat treatment. Heat input derives mainly from stirring and heat output mainly from losses to the surroundings. Residual heat input is removed by stabilized circulating thermostats. Temperature balance is due to spread out bare wire heaters which carry a current proportional to the state of the control DC Wheatstone bridge. The controlling thermistors are maintained in two oil baths and the state of the current in the control heaters is transmitted to the thermistors by a thermal feedback system involving small heating coils which are placed in the oil baths around the thermistors and which carry a current proportional to the heating cur

ISSN:0021-2148    

DOI:10.1002/ijch.197400097

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe redox‐properties of tetraphenylporphyrin‐complexes were studied as a function of substituents on the phenyl group. Electron‐withdrawing chlorine substituents cause a rise of approximately 100 mV for the first ligand oxidation and electron‐donating methoxy‐substituents cause a decrease of about the same magnitude. The redox‐properties of the central metal ion are much less sensitive to these substituents. The Fe3+/Fe2+transition on the other hand, is seen to depend on the anion used. Taking these effects into account a tentative mechanism is proposed for the oxidation‐behaviour of μ‐oxo‐bis (tetraphenyl)p

ISSN:0021-2148    

DOI:10.1002/ijch.197400098

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractAn electron paramagnetic resonance (EPR) study of the photoexcited triplet state of four free base porphyrins is presented. The zero field splitting parameters (ZFS) |D| and |E| were calculated from the EPR spectra of the porphyrins dissolved in n‐octane matrices at 80°K. |D| = 0.0359 cm−1, |E| = 0.0079 cm−1for tetra phenyl porphyrin (H2TPP), |D| = 0.0432 cm−1, |E| = 0.0037 cm−1for tetra (per‐fluoro) phenyl porphyrin H2T (per‐F) PP, |D| = 0.0366 cm−1, |E| = 0.0078 cm−1for tetra (para‐chloro) phenyl porphyrin H2T(P‐Cl)PP, |D| = 0.0369 cm−1, |E| = 0.0076 cm−1for tetra (para‐methyl) phenyl porphyrin H2T(P‐Me)PP. The transient behavior of the EPR signal intensities in the last two porphyrins is discussed. The depopulation rate constants of the triplet sublevels kp, the ratio between the population rate constants Ap(at zero field, p = x,y,z), and the spin lattice relaxation rate W within the triplet manifold, were calculated.kx= (12 ± 2) × 102sec−1, ky= (0.5 ± 0.1) × 102sec−1, kz= (1.2 ± 0.4) × 102sec−1, Ax:Ay:Az≃ 0.63:0.01:0.33, W = (0.4 ± 0.1) × 104sec−1for H2T(P‐Cl)PP, kx= (7 ± 2) × 102sec−1, ky= (4 ± 1) × 102sec−1, kz= (1.5 ± 0.5) × 102sec−1, Ax:Ay

ISSN:0021-2148    

DOI:10.1002/ijch.197400099

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe rates of reduction of some CoIIIpentaamine complexes by HINA·, and , HNA·, radicals were measured. It was found that HNA· is more reactive than HINA·. The redox potential for the couple HINA·/HINA+was calculated, E° = 0.80 ± 0.02 V. In the presence of large excess of NA, a catalytic enhancement in the reduction of CoIII(NH3)5NA and CoIII(NH3)5Pyridine by Eu2+was observed. The difference in the mechanism of reduction of CoIII(NH3)5X by Eu2+where X = NA or INA is discussed. The redox potential of the HNA·/HNA+couple was estimated, 0.80

ISSN:0021-2148    

DOI:10.1002/ijch.197400100

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe oxidation half‐wave potentials of Co2+tetraphenylporphyrin, measured by cyclic voltammetry in methylenechloride solution, are changed by the addition of weak bases like methanol, acetone and dimethylformamide. The wave corresponding to the metal‐oxidation Co2+⇄ Co3+is shifted to lower potential, while the wave, corresponding to the ligand oxidation Co3+(TPP) ⇄ Co3+(TPP)+. is shifted to higher potential. It can be shown, that this is due to a preferential interaction of Co3+(TPP) with the bases, which is stronger than that of the Co2+(TPP) as well as that of the Co3+(TPP)+. Because the shifts are proportional to the concentration of added base, they can be followed quantitatively and the equilibrium constants of the interactions between the different oxidation states and the bases can be calculated. The reduction wave of Co2+(TPP), corresponding to the Co3+⇄ Co1+transition is not changed by the weak bases, but is shifted to lower potential by pyridine and the picolines. The shift is again proportional to the concentration of added base. The reduction wave of Fe3−(TPP)Cl−is not changed by the weak bases, but is shifted to lower potential by pyridine. While the reduction wave of the free Fe3+(TPP)Cl−is irreversible, that of the pyridine‐adduct is reversible. In this case the shift is not proportional to the amount of added base. The voltammetric curves of the Cu, Ni, and Zn tetraphenyl‐porphyrins are not changed by the addition of either the weak

ISSN:0021-2148    

DOI:10.1002/ijch.197400101

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractOxygen was absorbed on cerium (IV) oxide which had been prepared by heating the cerium (III) oxalate at 1173°K in air. In addition to the naturally occurring isotope mixture of oxygen, an enriched17O2(67%) was adsorbed. From the enriched mixture it was concluded that the anionic species obtained was O−2. It was also shown that part of the oxygen was adsorbed as a molecular species. On this sample no isotopic exchange took place between the adsorbed (17O17O)−and (16O17O)−anion mol

ISSN:0021-2148    

DOI:10.1002/ijch.197400102

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY

ISSN:0021-2148    

DOI:10.1002/ijch.197400103

出版商:WILEY‐VCH Verlag    

年代:1974

数据来源: WILEY