Thermogravimetrische Untersuchung an den Kristallhydraten der Acetate einiger Zweiwertiger Metalle

Journal of Thermal Analysis and Calorimetry - Die Acetate Mg(OCOCH3)2 · 4H2O, Ca(OCOCH3)2 · H2O, Mn(OCOCH3)2 · 4H2O, Co(OCOCH3)2 · 4H2O, Ni(OCOCH3)2 · 4H2O,...     

Diffusion coefficients from stopped-flow gas chromatography

Summary Mutual diffusion coefficients of two gases A and B can be determined in an empty gas chromatographic column by letting component B enter at an intermediate position of the column and continuously flow through a part only of it, as a carrier gas. The other component A is injected in a small amount instantaneously at the closed end of the column with the detector placed at the other end. By repeatedly stopping and then restoring after a short time the flow of B, narrow extra peaks are produced on the chromatographic elution curve, owing to diffusion of A into B. An equation is derived giving the area under the curve of each stop-peak as a function of time of the corresponding stop. Plotting the experimental data according to this equation permits the determination of the diffusion coefficient of A into B. Some results obtained by this method show negligible variations with changes in the experimental parameters.     

Functionalization of substituted 2-(1H)pyridones. II. Synthetic pathways to c-6 modified 3-cyano- and 3-carboxy-2-(1H)pyridones from a common precursor

Starting from readily available 1,2-dihydro-6-methyl-2-oxo-3-pyridinecarbonitrile, 1, viable synthetic pathways to a number of C-6 functionalized 1,2-dihydro-2-oxo-3-pyridinecarbonitriles and corresponding acids are presented. Through the utilization of dianion chemistry, the C-6 methyl substituent is selectively functionalized to three different oxidation levels.     

Verbrückte und unverbrückte norbornyl-kationen in der gasphase. Berechnungen zur stabilität isomerer norbornyl-kationen mit hilfe quantenmechanischer verfahren

The geometry and the relative stability of bicyclic compounds 1–20 have been calculated by standard quantum mechanics methods.MINDO/3 yields the following stability order of isomeric norbornyl cations (relative energies in $\text{kcal}\text{mole}$): 1-norbornyl cation 9 (0.0); 1.7 σ-bridged cation 6 (0.7); 7-norbornyl cation (nonplanar) 7 (1.1); 2-norbornyl cation (classical) 2 (4.2); 7-norbornyl cation (planar) 8 (4.3); 2-norbornyl cation (bridged) 1 (6.1). The stability of the same ions calculated by ab initio methods (STO-3G, MINDO/3-geometry) leads to an order more nearly consistent with experimental results: 2-norbornyl cation (classical) 2 (0.0); 2-norbornyl cation (bridged) 1 (5.9); 7-norbornyl cation (planar) 8 (11.1); 1-norbornyl cation 9 (14.6); 7-norbornyl cation (nonplanar) 7 (21.2). For the secondary 7-norbornyl cation, MINDO/3 gives a pyramidal configuration, 3.2 $\text{kcal}\text{mole}$ more stable than the planar form. In contrast, the ab initio results (complete optimization of all geometrical parameters) indicate the planar cation to be the most stable form. The bridged structure of 2-norbornyl cation 1 is calculated (STO-3G, partly optimized) to be 4.3 $\text{kcal}\text{mole}$ less stable than the classical counterpart, 2. For the lower homologues 12 and 13 (STO-3G, complete geometry optimization), this difference is 6.4 $\text{kcal}\text{mole}$. However, more extended basis sets should favour the bridged structures. The hydrogen bridged norbornyl cations 3, 4, and 5 have been calculated (STO-3G, partly optimized) to be 14.4, 23.6 and 29.9 $\text{kcal}\text{mole}$ less stable than 2. The stability differences between the corresponding tertiary bicyclic ions 10 vs 11, and 14 vs 15 are calculated (ab initio) to be 15.3 and 19.0 kcal/mole, respectively, in favour of classical structures. The influence of methyl substitution at positions C₁ and C₆ (exo) on bridged and unbridged structure of 2-norbornyl cation is calculated. Pyramidal secondary and tertiary 2-norbornyl cations 19 (a; R=H, b; R=CH₃) and 20 (a; R=H, b; r=CH₃) have been used to model the electrical effects in the solvolysis transition states of epimeric 2-norbornyl esters. Due to more efficient hyperconjugation the pyramidal exo cation is stabilized more than the endo cation by 5.2 $\text{kcal}\text{mole}$ for the secondary series and 3.5 $\text{kcal}\text{mole}$ for the tertiary series. Bonding of endo cation 20 with a nucleophile should be stronger than bonding of exo cation 19 due to more efficient HOMO-LUMO interaction.     

Substituenteneffekte auf azido-tetrazolo-gleichgewichte elektronische und sterische effekte bei s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidinen1

The azido tetrazolo valence isomerism of twenty 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidines with different substituents at position 5 has been studied by means of ¹H NMR spectroscopy. All the compounds have been found to be tetrazoles in the solid state and in (CD₃)₂SO solution; in CF₃COOH azido and tetrazolo isomers are in equilibrium. From equilibrium constants K and thermodynamic data determined it is concluded that in this series K depends on both electronic effects and steric requirements of the 5-substituents. A linear relation between K and σ was found for 5-arylderivatives because ΔS° keeps approximately constant and the substituent mainly operates on ΔH°.     

The mechanism of the alkylation of isoxazolidin-3-one

In solvents of different polarities, the lactam-lactim tautomeric equilibrium of isoxazoli-din-3-one is strongly displaced in the direction of the lactam. The lactim form cannot be detected. It has been concluded that there is no connection between the dual chemical behavior of isoxazolidin-3-one and its potassium salt in the alkylation reaction with the equilibrium isomerization of these compounds. It has been shown that the mechanism of alkylation is connected with the structure of the lactam anion. Evidence is given in favor of a mesomeric structure of the anion with the main charge on the nitrogen at which substitution chiefly takes place.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 898–901, July, 1973.     

High-field NMR of ethylene—sulfur dioxide copolymers

Copolymers of ethylene and sulfur dioxide containing 40–60 wt-% sulfur dioxide have been analyzed by using 220 MHz high-resolution NMR, and it has been shown that they contain structures of the form, ? SO₂? (CH₂? CH₂)_n? SO₂? , where n is 1, 2, 3, 4, … The relative numbers of structures with n = 1, 2, 3, or 4 and above can be calculated from the NMR spectra. The fraction of ethylenes in longer blocks and the sulfur dioxide contents of the polymers can also be determined from the NMR data. The NMR results indicate that the distribution of ethylenes among the different structures is not that expected for a random copolymerization of ethylene and sulfur dioxide but that the arrangement of these structures within the copolymer is random.     

Chemical ionization mass spectrometry of nitrosamines

The mass spectra of eight nitrosamines have been recorded, with excitation by chemical ionization (CI) and electron impact (EI). Comparison of the intensities of the base peaks under CI and El conditions gives intensity ratios in the range 1.4-1.9 for low resolution measurements and up to 10 for high resolution measurements, confirming the enhanced sensitivity available in the CI mode.     

Modification chimique des polyalcadiènes par les composés du type CX3Z—I Addition catalysée des composés CCl3Z sur les polybutadiènes-1,2

The influence of catalysis on chemical modification of 1,2-polybutadienes (M_n < 10,000) by CX₃Z reagents (X = halogen; Z = functional group or halogen), in order to obtain polymers soluble in common solvents, has been studied. The work has been carried out with carbon tetrachloride, trichloromethylphosphonyldichloride (CCl₃POCl₂) and ethyl trichloroacetate (CCl₃CO₂Et) in the presence of solvents such as C₆H₆, CH₂Cl₂. Among the compounds tested as catalysts for the addition of CX₃Z to 1,2-polybutadiene (transition metal salts and complexes; radical initiators) only the systems formed with metal salts such as CuCl₂, FeCl₃, RuCl₃ 3H₂O, Fe₂(CO)₉ and Cl₂Ru(PPh₃)₃ were found to show high catalytic activity. The most active is Cl₂Ru(PPh₃)₃: used without or with cocatalysts (Et₃NHCl/benzôin, alcohols), it leads always, to the best yields whatever the nature of CX₃Z. The activity of the other catalysts is generally dependent on CX₃Z structure. Some secondary reactions (cross-linking, cyclization, transesterification) have been found.