Untersuchungen zur Acidität und Basizität von Alkoxysilylaminen

Investigations on Acidity and Basicity of Alkoxysilylamines Relative acidity and basicity have been determined for silylamines of the type (RO)₃Si? NH? X (R = Et, n. Pr, i-Pr, s-Bu, t-Bu; X = n-Bu, Ph, p-MeO? C₆H₄, p-Cl? C₆H₄, p-NO₂? C₆H₄) by IR, NMR, and potentiometric investigations. The position of the ν_NH band, the shift of this band in tetrahydrofuran and the chemical shift of NH-proton-NMR signal show a significant increase of NH acidity with increasing electron attracting effect of R and X. The shift of deuteriochloroform ν_CD band at association with aminosilanes and the results of potentiometric investigations confirm the low basicity of these compounds and the decrease of the basicity with increasing acidity.     

Untersuchungen zur Acidität und katalytischen Spaltaktivität dekationisierter NaY-Zeolithe

Investigation on Acidity and Catalytic Activity of Deep-Bed Calcinated Zeolites NH₄ NaY NMR and infrared techniques are applied to decationated zeolites NaY to study Brönsted acidity. The results are compared with measurements of catalytic activity and crystallinity of this zeolites. The number of OH groups which are able to form a pyridinium ion (PyH⁺) increases with increasing exchange degree and with increasing temperature of the sample. The rate of pyridinium ion formation as an equivalent of Brönsted acidity and the catalytic activity increase similarly with increasing exchange degree up to such values where a loss of crystallinity occurs.     

Untersuchungen zur Basizität von Alkyl- und Silylakylaminen

Investigations on the Basicity of Alkyl and Silyl Alkylamines The basicity of N has been investigated in primary and secondary alkyl und silyl alkylamines by means of the v_C–D band shift of CDCl₃ associated to the amine group by potentiometrically determined pK_s-values, and by mass spectroscopically measured ionisation potentials. The results show a dependence on electronic and steric effects, but they do not give arguments for a conjugative interaction between N and Si,     

Quantenchemische Untersuchungen zur Stabilität von Si—F-Spezies

Quantumchemical Investigations on the Stability of Si? F Species Semiempirical MO calculations (EHT, CNDO/2) have been used to examine the stability of Si—F-species (SiF₆^2?, SiF₄ planar and tetrahedral, SiF₃⁺ planar and pyramidal, and SiF₂ (SiF₂²⁺) linear and angled). The calculations showed, that the appearance of planar structures is possible from the energetical point in solid state reactions. In the case of SiF₂ (SiF₂²⁺) it was not possible to find an energetic difference between linear and not linear forms. The neutral form is energetic more stable than SiF₂²⁺. A comparison of investigated species shows, that with growing bonding angle and in this way with decreasing number of fluorine atoms in the molecule the bond lengths are decreased. The EHT-bond energies become more negative in the same way.     

Untersuchungen zur Stabilität und Reaktivität von (3-Cyclopropylidenprop-1-enyl)-ethyl-ether

Stability and Reactivity of 3-Cyclopropylideneprop-1-enyl Ethyl Ether 3-Cyclopropylideneprop-1-enyl ethyl ether ( 1 ) dimerizes to a cyclobutane derivative 2 which, upon prolonged heating, is converted to a cyclooctadiene ( 3 ). The reactivity of 1 is discussed. The structures of 2 and 3 as well as of their derivatives have been determined using ¹H-NMR spectroscopy and X-ray crystal-structure analysis.     

TAS‐Indolid und TAS‐Carbazolid: Strukturen von [TAS]+[IndHInd]− und [TAS]+[Carb]−·½CarbH

TAS Indolide and TAS Carbazolide: Structures of [TAS]⁺[IndHInd]^? and [TAS]⁺[Carb]^?·½CarbH From the reaction of TAS‐fluoride [(Me₂N)₃S]⁺[Me₃SiF₂]^? with trimethylsilyl‐indole and trimethylsilyl‐carbazole TAS‐indolide and TAS‐carbazolide are formed. During crystallisation partially protonation to indole and carbazole occurs, resulting in the formation of [TAS]⁺[IndHInd]^? ( 3a ) and [TAS]⁺[Carb]^?·½CarbH ( 5a ) according to X‐ray analysis.     

Mechanistical insight into ‘electrophilic’ trifluoromethylation with S-(trifluoromethyl)dibenzothiophenium salts

Trifluoromethyl sulfonium salts are widely used for the introduction of a trifluoromethyl group through reaction with a wide range of nucleophiles. Nevertheless, the reaction mechanism is far from obvious and has been the subject of various literature discussions. In this Letter, we show, through trapping experiments with a radical probe that, at least in the case of nucleophiles such as enol silyl ethers, the reaction proceeds by SET.     

Untersuchungen zur molekulargewichtsverteilung von polyäthylenterephthalat

The molecular weight distribution of carefully prepared thermostabilized poly(ethylene terephthalate) was determined immediately after polycondensation in vacuo (P?_n = 121) and after the melt was stirred at 280°C for 5.5 hr under nitrogen (P?_n = 123). The fractionation was carried out by successive precipitation in liquid phases. The samples were separated into 25 fractions including refractionation. The Flory distribution was observed in all samples.     

Theoretische Untersuchungen zur Basizität substituierter Pyridine

The applicability of the MINDO/3 method for the interpretation of the basicity of a series of substituted pyridines is critically discussed. Special attention is paid to the difference in thepK _a -values of the two isomeric 4,6-diamino-2-methoxy-(2) and 2,4-diamino-6-methoxy-3-pyridine-carbonitrile (3) (2=2.01,3=4.17). Based on the concept of charge- and orbital-controlled reactions this difference can be explained readily.