Search

The electron-accepting ability of 6,6-dicyanopentafulvenes (DCFs) can be varied extensively through substitution on the five-membered ring. The reduction potentials for a set of 2,3,4,5-tetraphenyl-substituted DCFs, with varying substituents at the para-position of the phenyl rings, strongly correlate with their Hammett σp-parameters. By combining cyclic voltammetry with DFT calculations ((U)B3LYP/6-311+G(d)), using the conductor-like polarizable continuum model (CPCM) for implicit solvation, the absolute reduction potentials of a set of twenty DCFs were reproduced with a mean absolute deviation of 0.10 eV and a maximum deviation of 0.19 eV. Our experimentally investigated DCFs have reduction potentials within 3.67-4.41 eV, however, the computations reveal that DCFs with experimental reduction potentials as high as 5.3 eV could be achieved, higher than that of F4-TCNQ (5.02 eV). Thus, the DCF core is a template that allows variation in the reduction potentials by about 1.6 eV.

[3+2]-cycloaddition reactions of aromatic azides and silylated alkynes in aqueous media yield 1,5-disubstituted-4-(trimethyl-silyl)-1H-1,2,3-triazoles. The formation of the 1,5-isomer is highly favored in this metal-free cycloaddition, which could be proven by 1D selective NOESY and X-ray investigations. Additionally, DFT calculations corroborate the outstanding favoritism regarding the 1,5-isomer. The described method provides a simple alternative protocol to metal-catalyzed "click chemistry" procedures, widening the scope for regioselective heavy-metal-free synthetic applications.

Methoxy poly(ethylene glycol) 2000 (mPEG 2000) samples were substituted via esterification reactions to convert the hydroxyl end group of the mPEG into potential initiators for the cationic ring opening polymerization of 2-oxazolines. These substitution products were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS); in addition, detailed MALDI-TOF/TOF-collision induced dissociation (CID) MS studies were performed to introduce this method as complementary structural characterization tool allowing the detailed analysis of the prepared macromolecules. The CID of the macroinitiators revealed 1,4-hydrogen and 1,4-ethylene eliminations forming very regular fragmentation patterns which showed, depending on the end groups, different fragmentation series. Furthermore, very pronounced McLafferty + 1 rearrangements (1,5 hydrogen-transfer) of the introduced ester end groups were observed leaving the mPEG molecule as neutral acid. This incisive loss revealed the exact molar mass for each end group and, therefore, represents an important tool for end group determination of functionalized polymers.

The impact breccias encountered in drill hole Yaxcopoil-1 (Yax-1) in the Chicxulub impact structure have been subdivided into six units. The two uppermost units are redeposited suevite and suevite, and together are only 28 m thick. The two units below are interpreted as a ground surge deposit similar to a pyroclastic flow in a volcanic regime with a fine-grained top (unit 3; 23 m thick; nuee ardente) and a coarse breccia (unit 4; approx.15 m thick) below. As such, they consist of a melange of clastic matrix breccia and melt breccia. The pyroclastic ground surge deposit and the two units 5 and 6 below are related to the ejecta curtain. Unit 5 (approx.24 m thick) is a silicate impact melt breccia, whereas unit 6 (10 m thick) is largely a carbonate melt breccia with some clastic-matrix components. Unit 5 and 6 reflect an overturning of the target stratigraphy. The suevites of units 1 and 2 were deposited after emplacement of the ejecta curtain debris. Reaction of the super-heated breccias with seawater led to explosive activity similar to phreomagmatic steam explosion in volcanic regimes. This activity caused further brecciation of melt and melt fragments. The fallback suevite deposit of units 1 and 2 is much thinner than suevite deposits at larger distances from the center of the impact structure than the 60 km of the Yax-1 drill site. This is evidence that the fallback suevite deposit (units 1 and 2) originally was much thicker. Unit 1 exhibits sedimentological features suggestive of suevite redeposition. Erosion possibly has occurred right after the IUT impact due to seawater backsurge, but erosion processes spanning thousands of years may also have been active. Therefore, the top of the 100 m thick impactite sequence at Yaxcopoil, in our opinion, is not the K/T boundary.

The Wanapitei impact structure is approximately 8 km in diameter and lies within Wanapitei Lake, approximately 34 km northeast of the city of Sudbury. Rocks related to the 37 Ma impact event are found only in Pleistocene glacial deposits south of the lake. Most of the target rocks are metasedimentary rocks of the Proterozoic Huronian Supergroup. An almost completely vitrified, inclusion-bearing sample investigated here represents either an impact melt or a strongly shock metamorphosed, pebbly wacke. In the second, preferred interpretation, a number of partially melted and devitrified clasts are enclosed in an equally highly shock metamorphosed arkosic wacke matrix (i.e., the sample is a shocked pebbly wacke), which records the onset of shock melting. This interpretation is based on the glass composition, mineral relicts in the glass, relict rock textures, and the similar degree of shock metamorphism and incipient melting of all sample components. Boulder matrix and clasts are largely vitrified and preserve various degrees of fluidization, vesiculation, and devitrification. Peak shock pressure of approximately 50-60 GPa and stress experienced by the sample were somewhat below those required for complete melting and development of a homogeneous melt. The rapid cooling and devitrification history of the analyzed sample is comparable to that reported recently from glasses in the suevite of the Ries impact structure in Germany and may indicate that the analyzed sample experienced an annealing temperature after deposition of somewhere between 650 C and 800 C.

The pulse radiolysis of 5-chlorouracil (ClUr) in airfree aqueous solution has been investigated. The rate constants for the reactions of the formation and the decay of the 5-chlorouracil radical anion presented in the following reaction scheme have been measured at 21 °C: k1 =(2.2 ± 0.4) · 1010 M−1 s−1, k2 =(9 ± 2) · 104 s−1, k3 =(3.3 ± 0.6) · 1010 M−1 s−1, k-3 = (3.3 ± 0.6) · 105 s−1, 2k4 = (6.6 ± 1.2) · 109 M−1 s−1; k1 agrees with the values so far measured [1, 2]; the other rate constants have not been determined before. – The dissociation of ClUr. (reaction (2)) proceeded with an activation energy Ea = (10.5 ± 1) kcal/mol (44 kJ/mol) and an entropy of activation ΔS≠ (25°C) = -(1 ± 5) eu. – The value of the dissociation constant was determined by two independent methods which lead to the same value (pK3 = 5.0 ± 0.2 at 21°C). – Computer simulations using the obtained k values gave good agreement for the decay and the subsequent rise of the conductivity after pulse. – G-values under 60Co-γ-irradiations of 5-chlorouracil in aqueous de-aerated solutions containing tert.-butanol were: G (-ClUr) = 3.2 ± 0.3/100 eV, G (Ur) = 2.7 ± 0.2/100 eV and G (Cl−) = 2.7 ± 0.1/100 eV, at pH values of 6.5 (buffered) and 4.7 (unbuffered). – Under pulse conditions the yield of chloride was G (Cl−) = 2.7 ± 0.2/100 eV in neutral and alcaline solutions, but was lower in acidic solutions (pH < 5) and at higher dose rates. This result was interpreted in terms of reaction (4). Die Pulsradiolyse des 5-Chlouracils wurde in entgaster, wasriger Losung untersucht und die Geschwindigkeitskonstanten der Reaktionen des 5-Chloruracilradikalanions, wie sie im folgenden Reaktionsschema dargestellt sind, gemessen: k1 = (2,2 ± 0,4) · 1010 M−1 s−1, k2 = (9 ± 2) · 104 s−1, k3 = (3,3 ± 0,6) · 1010 M−1 s−1, k-3 = (3,3 ± 0,6) · 105 s−1, 2k4 = (6,6 ± 1,2) · 109 M−1 s−1; k1 stimmt mit bereits gemessenen Werten uberein [1, 2]. – Die Dissoziation von ClUr.− (Reaktion (2)) lauft mit einer Aktivierungsenergie Ea = (10,5 ± 1) kcal/mol (44kJ/mol) und mit einer Aktivierungsentropie ΔS≠ (25°C) = –(1 ± 5) eu ab. – Die Dissoziationskonstante pK3 wurde mit zwei voneinander unabhangigen Methoden bestimmt, die beide zu demselben Wert fuhrten (pK3 = 5,0 ± 1). – Simulationsrechnungen fur den Verlauf der Leitfahigkeitskurven fuhrten zu einer guten Ubereinstimmung mit dem Experiment. – Die G-Werte einer 60Co-γ-bestrahlten, wasrigen und entgasten Losung von 5-Chloruracil mit tert. -Butanol waren: G (-ClUr) = 3,2 ± 0,3/100 eV, G (Ur) = 2,7 ± 0,2/100 eV und G (Cl−) = 2,7 ± 0,1/100 eV, sowohl in gepufferter Losung bei pH 6,5 als auch ungepuffert bei pH 4,7. – Unter Pulsbedingungen betragt G (Cl−) = 2,7 ± 0,2/100 eV in neutraler sowie alkalischer Losung, er war jedoch geringer in saurer Losung (pH < 5) und bei hoherer Dosis. Dieses Ergebnis wird durch den Einflus der Reaktion (4) erklart.

Entscheidung der OECD zur gegenseitigen Anerkennung der Daten bei der Bewertung von Chemikalien

Die Ausbeuten an Haq+ und OHaq− wurden nach der Pulsradiolyse von neutralem Wasser mit Hilfe einer Leitfahigkeitsmeseinrichtung neu bestimmt. Die Werte in Argon-gesattigter Losung 0.5 μs nach einem 1 μs Bestrahlungsimpuls mit 2,8 MeV Elektronen sind: G(Haq+)Ar = (3.3 ± 0.25)/100eV, G(OHaq−)λr = 0.60 ± 0.25 (unter der Voraussetzung G(eaq−) = 2,7); mit 10−1 mol/1 Athanolzusatz betragt G(eaq−) = 3.2 (optisch gemessen), G(OHaq−) = 0.1 und G(Haq−) = 3,3. In N2O-gesattigter Losung betragen G(Haq+)N2O = G(OHaq−)N2O = 2,9 ± 0,25. Die Wirkungen der Zusatze werden als Spureffekte gedeutet. The initial yields of Haq+ and OHaq− have been remeasured in neutral water by pulse radiolysis using conductivity. The values 0.5 μs after a 1 μs pulse of 2.8 MeV electrons in Ar saturated solution are: G(Haq+)Ar = (3.3 ± 0.25)/100 eV, G(OHaq−)Ar = 0.60 ± 0.25 (under the assumption of G(eaq−) = 2.7), with 10−1 mol/1 ethanol as additive G(eaq−) = 3.2 (optically measured), G(OHaq−) = 0.1 and G(Haq+) = 3.3. In N2O saturated solution G(Haq+)N2o = 2.9 ± 0.25 and G(OHaq−)N2O = 2.9 ± 0.25 have been found. The effect of the additives is explained on the base of spur reactions.

Der Zusatz von Hexamethylphosphorsauretriamid (HMPT) zu den atherischen Losungen von benzylartigen Organomagnesium-Verbindungen fuhrt zu drastischen, spektral beobachtbaren Veranderungen. Zunachst tritt eine scheinbar kontinuierliche Verschiebung der Absorptionsmaxima nach langeren Wellen ein, bis zwei Aquivalente des starken Donor-Solvens zugesetzt sind. Weitere Zugabe von HMPT fuhrt zur Ionisation der CMg-Bindungen und Freisetzung der betreffenden Carbanionen, die sich durch das Aufkommen der (von den Alkalimetall-Verbindungen bekannten) Carbanion-Banden zu erkennen gibt. Ionization of Organomagnesium Compounds, IV. Formation of Carbanions from Organomagnesium Compounds by Means of Hexamethyl-phosphortriamide Stepwise addition of hexamethylphosphortriamide (HMPT) to the solutions of benzyl-like organomagnesium compounds in diethylether results in drastic changes which can be observed spectroscopically. First, the absorption maxima are shifted to longer wave lengths in an apparently continuous manner, until two equivalents of the strongly donating cosolvent have been added. Further addition of HMPT leads to ionization of the CMg-bonds. This can be seen from the development of new bands characteristic of the carbanions, as represented by the alkali metal derivatives.

In konzentrierten atherischen Losungen liegen Grignard-Verbindungen uberwiegend in der Form R_2Mg + MgX_2 vor. Die ^(13)C-chemischen Verschiebungen aliphatischer Grignard-Verbindungen sind linear korrelierbar mit denen entsprechender Kohlenwasserstoffe. Allyl-und Cyclopentadienylmagnesiumbromid zeigen austauschentartete ^(13)C-Spektren. Fur alkyl-substituierte Benzole konnten die Linien zugeordnet werden. ^(13)C-NMR-Spectroscopic Investigations of Grignard Compounds Grignard reagents occur predominantly as R_2Mg + MgX_2 in concentrated diethyl ether solutions. The ^(13)C chemical shifts of Grignard reagents give a linear correlation with the chemical shifts of corresponding hydrocarbons. Exchange processes produce degenerate ^(13)C spectra for allyl- and cyclopentadienylmagnesium bromide. The resonance lines for alkyl-substituted benzenes have been assigned to specific carbons.

Die UV-Absorptionen von Phenyl-, Benzyl- und verwandten Organomagnesium-Verbindungen 1-7 in Diathylather werden gemessen und storungstheoretisch diskutiert. Die Banden der benzylartigen Magnesiumverbindungen nehmen eine mittlere Lage zwischen den Banden der zugrunde liegenden Kohlenwasserstoffe und der durch die Alkalimetall-Derivate reprasentierten Carbanionen ein, woraus auf einen betrachtlichen Ionencharakter der Organo-magnesium-Verbindungen mit potentieller Ladungsdelokalisation geschlossen wird. Die Mittelstellung zwischen kovalenten und ionischen Strukturen last eine starke Beeinflusbarkeit dieser Systeme durch das Losungsmittel erwarten. Ionization of Organomagnesium Compounds, III. U. V. Spectroscopic Demonstration of Carbanionic Character in Ethereal, Benzyl-like Organomagnesium-Compounds The u. v. absorptions of phenyl-, benzyl-, and related organomagnesium compounds 1-7 in diethylether are measured and discussed on the basis of perturbation theory. The absorption bands of the benzyl-like magnesium compounds are situated midway between those of the corresponding hydrocarbons and carbanions, as represented by the alkali metal compounds. It is concluded that organomagnesium derivatives of systems with potential charge delocalization are distinguished by a remarkable degree of ionic character. Strong solvent effects on these compounds are to be expected.