N-quaternary compounds—XLIV: Synthesis and circular dichroism of α-N,N-dimethylamino and α-N,N,N-trimethylammonio ketones

CD spectra of acyclic α-N,N-dimethylamino ketones exhibit two absorption bands of opposite sign at ca. 240 and 305–315 nm. Both bands are ascribed to the same conformers. On protonation only one CD band is seen. The single CD band of α-N,N,N-trimethylammonio ketones has the same sign and almost the same wavelength maximum as the protonated amino ketones.     

Mechanisms for the solvolytic decompositions of nucleoside analogues—I: Acidic hydrolysis of 2-substituted 1-(1-ethoxyethyl)benzimidazoles

A few 2-substituted 1-(1-ethoxyethyl)benzimidazoles have been prepared and the rate constants for their hydrolysis measured at various temperatures and oxonium ion concentrations. The formal kinetics followed and the effect of varying the 2-substitution on the hydrolysis rate suggest that the acid-catalyzed cleavage of these compounds involves a rapid initial protonation of the benzimidazole ring and a subsequent rate-limiting heterolysis of the protonated substrate to form a free nitrogen base and an ocarbenium ion derived from the ethoxyethyl group. The values obtained for the entropy of activation are consistent with the assumed unimolecular nature of the rate-limiting step. The effects of 2-substituents on the acidities of the protonated substrates and their heterolysis rates have been compared. The latter partial reaction has been suggested to be the subject of steric acceleration.     

The determination of sulphur in copper,nickel and aluminium alloys by proton activation analysis

The ³⁴S(p, n)^34mCl reaction induced by 13-MeV protons is used for the determination of sulphur in copper, nickel and aluminium alloys. The ^34mCl is separated by repeated precipitation as silver chloride. The results obtained were 3.08 ± 0.47, 1.47 ± 0.17 and <1μg g^-1 for copper, nickel and aluminium alloys, respectively.     

Reversed-phase ion-pair partition chromatography of carboxylates and sulphonates.

A reversed-phase partition chromatographic system for separation of organic anions as ion pairs with quaternary ammonium ions has been developed. Commercial, hydrophobized silica supports are used with 1-pentanol as stationary phase and aqueous solutions of tetrabutylammonium (TBA) as mobile phase. The separation of the aromatic sulphonates and benzoic acid derivatives is demonstrated. The use of the TBA concentration of the mobile phase to regulate the capacity factor of the anions, as a means of improving separation by gradient elution and direct injection of large sample volumes, is demonstrated. The isolation of nicotinic acid from human serum samples is shown.     

A comparison of SCF-Xα and extended Hückel methods for metal clusters

A comparison of some results from Xα-scattered wave (Xα-SW) and extended Hückel (EH) calculations for metal clusters is given. It is found that small clusters of atoms (≈ 13 atoms) using the Xα-SW method reproduce many of the features of the electronic structure of the bulk metals, whereas this is not the case for the same clusters using the EH method. A more systematic approach to EH parametrizations is suggested in order to make this method a more viable approach to treating metal clusters.     

Antimon-organo-Verbindungen. V. Zum Reaktionsverhalten des Phenylstibins

Organoantimony Compounds. V. The Reactivity of Phenyl Stibine C₆H₅SbH₂, synthesized by the reduction of C₆H₅SbCl₂ with LiBH₄, reacts with LiR under certain conditions forming (C₆H₅Sb)_n and H₂ or give by a partially elimination of H₂ stibides with a different structure. The latter react with alkyl and aryl halides forming tert. stibines which may be characterized as the corresponding dibromides. The preparation of C₆H₅SbNa₂ and its reaction with C₂H₅Br, Cl(CH₂)₄Cl and C₆H₅(Cl)C?N? N?C(Cl)C₆H₅ are described.     

Synthesis and structural characterization of acetatobis(triphenylphosphine)dicarbonylmanganese(I), (CH3CO2)Mn(CO)2[P(C6H5)3]2: An organometallic complex containing a chelating acetate ligand

The accidental but intriguing synthesis of acetatobis(triphenylphosphine)dicarbonylmanganese(I), (CH₃CO₂)Mn(CO)₂[P(C₆H₅)₃]₂, has been accomplished by the reaction of NaMn(CO)₅ with (CH₃)₃SiCl followed by the addition of triphenylphosphine and acetic acid. A three-dimensional single-crystal X-ray diffraction analysis has shown an octahedral-like molecule containing a symmetrically oxygen-chelating acetate group, the first such group to be reported in a metal carbonyl complex. The two triphenylphosphine ligands occupy mutually trans positions with the two carbonyl ligands possessing the remaining cis sites in the octahedral complex. The compound crystallizes with four molecules in a monoclinic unit cell of space group symmetry $\text{P}\text{2}{}_1\text{c}$ and of dimensions a = 17.744(2) Å, b = 9.692(1) Å, c = 20.004(2) Å, and β = 106.195(4)°. The relatively long MnO(acetate) bond lengths [2.066(6) and 2.069(7) Å] and the relatively short MnCO bond lengths [1.701(12) and 1.760(13) Å] and the relatively short MnP(C₆H₅)₃ bond lengths [2.260(3) and 2.275(3) Å], compared to the corresponding MnCO and MnP(C₆H₅)₃ bond lengths in other manganese carbonyl triphenylphosphine complexes, are rationalized on the basis that the acetate ligand in this molecule functions primarily as a σ-donor.