Conductances of some electrolytes in 2-methylpyridine-N-oxide at 55°C

Conductance measurements for fifteen uni-univalent salts in 2-methylpyridine-N-oxide (2-MPO) were made over the concentration range of 2–120×10^–4 mol-dm^–3 at 55°C. All conductance data were evaluated by the Lee-Wheaton equation. The results indicate that all of the salts studied are slightly associated in 2-MPO, which is, nevertheless, a reasonably good ionizing solvent compared to other solvents having a similar value for the dielectric constant. The tetraalkylammonium halides are weaker electrolytes than the tetraphenylborate salts in 2-MPO. Ionic limiting molar conductances were obtained by using as a reference electrolyte tris(iso-pentyl)butylammonium tetraphenylborate. Anions appear to be poorly solvated in this solvent but certain cations, particularly Na⁺ and K⁺, show evidence of specific ion-solvent interaction.This study was presented, in part, at the 6th Central Regional Meeting of the American Chemical Society, Detroit, Michigan, April 1974.     

Some thermodynamic properties of carboxylato-pentammine cobalt(III) ions

Measurements are reported on the thermodynamic properties for the acid ionisation of various carboxylato-pentammine cobalt(III) ions, where the organic ligand is a dicarboxylate ion ^?OCORCOOH. It is shown that the results can be correlated with the ionisation of the free acids, on the basis of a simple electrostatic model. Results are also reported on the enthalpies of hydrolysis of the same ions, obtained indirectly from the enthalpies of reaction with sodium sulphide. The results for the complexes of the dicarboxylic acids which were studied (maleato, phthalato, fumarato, succinato and malonato) are not very different, while the acetato complex is somewhat more unstable. There is some indication that the complexes which hydrolyse faster are also thermodynamically less stable.     

Conductance behavior of 1:1 electrolytes in 3-methyl-2-oxazolidone at 25°C

The conductance behavior of twenty-five 1∶1 electrolytes has been investigated in 3-methyl-2-oxazolidone (3Me20x) at 25°C. Conductance data were analyzed by the Lee-Wheaton equation, and all salts studied were found to be only slightly associated. Ionic limiting equivalent conductances were obtained using tris(iso-pentyl)butylammonium tetraphenylborate as a reference electrolyte. The relative values of the ionic limiting molar conductance are generally similar to those for other dipolar aprotic solvents. However, the order $$\lambda _0 (i - Pent_3 BuN^ + ) > \lambda _0 (Pent_4 N^ + )and\lambda _0 (Br^ - ) > \lambda _0 (ClO_4^ - )$$ is opposite to that found previously in the similar solvent 3-tert-bytyl-2-oxazolidone.     

Aqueous partial molar heat capacities and volumes for NaTcO4 and NaReO4

A flow microcalorimeter/densimeter system has been commissioned to measure heat capacities and densities of solutions containing radioactive species as a function of temperature. Measurements were made for NaTcO₄(aq) at six temperatures (189.15 K to 373.15 K for the heat capacities, 287.43 K to 396.67 K for the densities) over the molality range 0.01 to 0.29 mol-kg^–1. Measurements for NaReO₄(aq) (NaReO₄ is a common nonradioactive analogue for NaTcO₄) were made under similar conditions, but for eight temperatures and a more extensive range of molalities, 0.05 to 0.65 mol-kg^–1. Heat capacities of NaCl(aq) reference solutions were also measured from 293.15 K to 398.15 K.The heat capacity and density data are analysed using Pitzer's ioninteraction model. Equations for the apparent molar heat capacities and volumes are reported. Values of the NaReO₄(aq) partial molar heat capacities are compared to literature values based on integral heats of solution. The agreement between the two sets of NaReO₄ results is good below 330 K, but only fair at the higher temperatures. Values of the partial molar volumes have also been derived. Using literature values and the results of our experiments, it is calculated that the disproportionation of hydrated TcO₂(s) to form TcO ₄ ^– (aq) and Tc(cr) occurs more readily at high temperatures. The uncertainties introduced by using thermodynamic values for ReO ₄ ^– (aq), in the absence of values for TcO ₄ ^– (aq), are discussed.     

Nucleophilic addition to 3-substituted pyridinium salts: expedient syntheses of (-)-L-733,061 and (-)-CP-99,994

[reaction: see text] The addition of nucleophiles to 3-substituted pyridinium salts prepared from N-methylbenzamide and various pyridines has been investigated. Good to excellent regioselectivities favoring the 2,3-disubstituted 1,2-dihydropyridines were observed. The resulting 1,2-dihydropyridines led to the corresponding 2,3-disubstituted pyridines upon treatment with Mn(OAc)3/NaIO4. This methodology was also successfully applied to the enantioselective syntheses of (-)-L-733,061 and (-)-CP-99,994, two members of a new class of highly potent, nonpeptide, Substance P antagonists.     

Equivariant Euler characteristics of discriminants of reflection groups

Let G be a finite, complex reflection group acting on a complex vector space V, and δ its disciminant polynomial. The fibres of δ admit commuting actions of G and a cyclic group. The virtual G × C_m character given by the Euler characteristics of a fibre is a refinement of the zeta function of the geometric monodromy, calculated in [8]. We show that this virtual character is unchanged by replacing δ by a slightly more general class of polynomials. We compute it explicitly, by studying the poset of normalizers of centralizers of regular elements in G, and the subspace arrangement given by the proper eigenspaces of elements of G. As a consequence we also compute orbifold Euler characteristics and find some new ‘case-free’ information about the discriminant.     

Stereo- and Regiochemical Effect of N,N-Dialkylamide Extractants on the Speciation of Pu Complexes

The relationship between extractant stereochemistry and their extraction performance has only poorly been established. In order to address a part of this concern, we investigated the Pu(IV) liquid-liquid extraction (LLE) by using the N,N-di-(2-ethylhexyl)butyramide (DEHBA), as well as those of its position isomers. DEHBA (ββ-isomer) and N-(2-ethylhexyl)-N-(oct-3-yl)butyramide (EHOBA or αβ-isomer) were synthesized as a mixture of stereoisomer or stereoenriched (R,S)- and (S,S)-diastereoisomers, and were all assessed for Pu^IV LLE. The results showed that both the position and the stereoisomerism of the aliphatic substituents affect Pu^IV complexation and extraction. We found that Pu extraction is lowered by factor 2 to 4 when the ethyl branching group is closer to the complexing site. UV-vis spectroscopy showed that this extraction decrease was affected by steric hindrance inducing a deprivation of Pu inner sphere complex. Effect of stereoisomerism is highlighted for branching closer to the complexing site (α-position). Enantiopure DEHBA stereoisomers provided similar Pu extraction, whereas a slight decrease could be noticed for the more cluttered stereoenriched (αβ)-isomers, which was also concomitant with a smaller population of inner sphere complex. In contrast, the stereoisomers mixture led to a strong decrease of Pu extraction because of an antagonistic association in the mixed complexes.     

Time series classification by class-specific Mahalanobis distance measures

To classify time series by nearest neighbors, we need to specify or learn one or several distance measures. We consider variations of the Mahalanobis distance measures which rely on the inverse covariance matrix of the data. Unfortunately??for time series data??the covariance matrix has often low rank. To alleviate this problem we can either use a pseudoinverse, covariance shrinking or limit the matrix to its diagonal. We review these alternatives and benchmark them against competitive methods such as the related Large Margin Nearest Neighbor Classification (LMNN) and the Dynamic Time Warping (DTW) distance. As we expected, we find that the DTW is superior, but the Mahalanobis distance measures are one to two orders of magnitude faster. To get best results with Mahalanobis distance measures, we recommend learning one distance measure per class using either covariance shrinking or the diagonal approach.