Showing papers in "Angewandte Chemie in 1975"
TL;DR: The formation of ozonides (1,2,4-trioxolanes) from alkenes and ozone can be described as a succession of three [2+3] cycloadditions or cycloreversions involving primary ozone oxides and aldehyde or ketone oxides as decisive intermediates as mentioned in this paper.
Abstract: The formation of ozonides (1,2,4-trioxolanes) from alkenes and ozone can be described as a succession of three [2+3] cycloadditions or cycloreversions involving primary ozonides (1,2,3-trioxolanes) and aldehyde or ketone oxides as decisive intermediates, all of which have finite lifetimes. There is no warranted experimental basis for assuming an alternative mechanism.
1,077 citations
TL;DR: In this article, a review of the processes occurring on the treatment of triphenylphosphane with tetrachloromethane are first reported; a key role is played here by (trichlormethyl)phosphonium chloride which reacts with a further amount of the phosphane to give the stable salt [chloro(triphenyl phos-phoranediyl)methyl]triphenynphosphoni chloride by way of dichlorophosphorane and (dichloromethemylene)ph phosphorane that is detectable only
Abstract: In this review the processes occurring on the treatment of triphenylphosphane with tetrachloromethane are first reported; a key role is played here by (trichloromethyl)phosphonium chloride which reacts with a further amount of the phosphane to give the stable salt [chloro(triphenylphos-phoranediyl)methyl]triphenylphosphonium chloride by way of dichlorophosphorane and (dichloromethylene)phosphorane that is detectable only as an intermediate. The preparative application of the two-component system as a chlorinating, dehydrating, and P—N-linking reagent is ascribable to “phosphorylation” of the substrate in question through several reactive species. In these applications the reactions with the substrate compete with reactions of the two-component system with itself, so that the overall course of the reaction is in nearly all cases much more complex than was previously assumed. Nevertheless. very good results can be achieved by the use of this reagent, high yields and mild reaction conditions being characteristic.
784 citations
TL;DR: In this article, the driving forces leading to the formation of ternary Cu2+ complexes are outlined; they are (i) statistical reasons, neutralization of charge in the mixed-ligand complexes, steric factors (bulky groups, ring size of chelates), and formation of π bonds.
Abstract: The driving forces leading to the formation of ternary Cu2+ complexes are outlined; they are (i) statistical reasons, (ii) neutralization of charge in the mixed-ligand complexes, (iii) steric factors (bulky groups, ring size of chelates), and (iv) formation of π bonds. The last point is important for achieving a large stability, as well as for the observation of discriminating qualities. An additional stability increase may possibly be achieved through a direct interaction between the two ligands bound to the same metal ion, i.e. Schiff base formation, hydrogen bonding or a charge-transfer relation. The latter leads to distinct structures, i.e. metal ion-bridged charge-transfer complexes. The relation between stability and structure on the reactivity of mixed-ligand complexes is emphasized. The relevance of the results for mixed-ligand complexes containing metal ions other than Cu2+ is briefly outlined.
301 citations
TL;DR: A review of recent developments in parts of the field of interest to me can be found in this paper, where the authors point out some of the principles operative in the photochemistry of organic crystals.
Abstract: During the years that he was at the Weizmann Institute of Science the late G. M. J. Schmidt initiated and developed a very vital research program on the relationship between the structures of organic crystals and the reactions which occur in these crystals. As the program developed the “solid-state group” became larger and more diversified—X-ray crystallographers, organic chemists, spectroscopists, and even theoreticans had their contributions to make. Professor Schmidt died in 1971. As one of the members of this group, I here present a review of recent developments in parts of the field of interest to me.
Of the reactions of organic crystals which have been studied thus far a large number are induced by light and other radiation. This is because radiation, unlike most chemical reactants, can readily penetrate the surface of the crystal, and thus reach the sites one wishes to activate. It is my aim in this article to point out some of the principles operative in the photochemistry of organic crystals. I shall choose examples to illustrate these principles and will not attempt to cover all the various types of reaction and systems which have been studied.
It is appropriate at this stage to pay tribute to the memory of another great scientist who recently passed away—Theodorr Foster. Many of the ideas which I develop here are extensions of Professor Forster's earlier work, as are so many of the recent developments in photochemistry.
281 citations
267 citations
TL;DR: In this article, the Umsetzung von Triphenylphosphan with Tetrachlormethan ablaufenden Vorgange berichtet.
Abstract: In diesem Beitrag wird zunachst uber die bei der Umsetzung von Triphenylphosphan mit Tetrachlormethan ablaufenden Vorgange berichtet. Eine Schlusselrolle kommt dabei dem Trichlormethylphosphoniumchlorid zu, das mit weiterem Phosphan uber die Stufe des nur als Zwischenprodukt nachweisbaren Dichlormethylenphosphorans und des Dichlorphosphorans zum stabilen Salz Triphenylphosphorandiylchlormethyl-triphenylphosphoniumchlorid reagiert. Die praparative Anwendung des Zweikomponentensystems als Chlorierungs-, Dehydratisierungs-und PN-Verknupfungs-Reagens ist auf die „Phosphorylierung” 1 des jeweiligen Substrats durch mehrere reaktive Spezies zuruckzufuhren. Hierbei konkurrieren die Substratreaktionen mit den Eigenreaktionen des Zweikomponentensystems, so das der Gesamtreaktionsverlauf in fast allen Fallen weit komplexer als fruher angenommen ist. Dennoch lassen sich mit diesem Reagens sehr gute Ergebnisse erzielen, fur die hohe Ausbeuten und milde Reaktionsbedingungen charakteristisch sind.
264 citations
TL;DR: It is of interest that a number of groups which do not behave as leaving groups in SN2 displacements are readily displaced at room temperature from a satureted carbon atom via the radical anion-free radical pathway, e.g., nitro, azide, sulfone, and ether groups.
Abstract: A new type of substition process at a saturated carbon atom is described. These reactions, which proceed via a chain sequence in which radical anions and free radicals are intermediates, are noteworthy for providing novel and powerful means of synthesis: they occur readily under mild conditions, they give excellent yields of pure products, and, in contrast to SN2 displacements, they are rather insensitive to steric hindrance. As a consequence, radical anion processes are especially valuable for the preparation of highly branched structures. Many inorganic and organic anions readily enter into these displacements and, indeed, amines are also effective. Systems which undergo substitutions via this electron transfer mechanism include benzylic, cumylic, strictly aliphatic, and heterocyclic molecules. It is of interest that a number of groups which do not behave as leaving groups in SN2 displacements are readily displaced at room temperature from a satureted carbon atom via the radical anion-free radical pathway, e.g., nitro, azide, sulfone, and ether groups.
257 citations
249 citations
220 citations
TL;DR: In this article, the authors show that SS bonds are extraordinarily flexible and have properties that are observed only on isolated occasions for other homonuclear bonds: the bond lengths very between 1.8 and 3.0A, the bond angles between 90 and 180° and the dihedral angles between 0 and 360°; the bond energies amount to up to 430 kJ/mol.
Abstract: SS bonds are extraordinarily flexible and have properties that are observed only on isolated occasions for other homonuclear bonds: the bond lengths very between 1.8 and 3.0A, the bond angles between 90 and 180° and the dihedral angles between 0 and 180°; the bond energies amount to up to 430 kJ/mol. The SS stretching frequencies can appear over the range 177–820 cm−1 and force constants of 1.4 to 6.3 mdyne/A have been calculated. This variability is illustrated with examples containing isolated and cumulated SS bonds.
214 citations
TL;DR: The readily accessible α-diazo carbonyl compounds are distinguished by their high reactivity, which opens up a variety of preparative applications under modified conditions as mentioned in this paper, and Wolff rearrangements of these compounds, induced thermally, photochemically or catalytically, afford ketenes.
Abstract: The readily accessible α-diazo carbonyl compounds are distinguished by their high reactivity, which opens up a variety of preparative applications under modified conditions. Wolff rearrangements of these compounds, induced thermally, photochemically, or catalytically, afford ketenes. Free and complexed carbenes, 1,3-dipoles, 1,3-diradicals, and the antiaromatic oxirenes have been considered as intermediates or transition states. The present progress report attempts to integrate preparative and theoretical aspects.
TL;DR: In this article, the structural changes of a given molecular fragment are correlated with each other, and the observed mutual dependence (structural correlation) may be described by means of Pauling's equation relating bond length r to bond number n:r = r 0 - clogn.
Abstract: The three-dimensional structure of frequently occurring molecular fragments has been studied systematically. Molecular subunits which were examined include hydrogen bridges (O—HċO), triiodide anions (I−3), other linear triatomic fragments (Cl—SbċCl, S—SċS, Mo—OċMo), tetrahedral ions (SO2−4, PO3−4, AlCl−4) and related species (MSO3, etc.), molecules containing both keto- and amino-groups (mostly alkaloids), substituted [10]annulenes and cycloheptatrienes, organic five-membered rings, and five-coordinated metal and nonmetal atoms. The bond distances and angles describing the structure of a giving fragment cover a range that is many times larger than the range of the experimental standard deviations. The changes of the various structural parameters of a fragment are correlated with each other. The observed mutual dependence (structural correlation) may be described by means of Pauling's equation relating bond length r to bond number n:r = r0 - clogn. The bond numbers n are expressed in terms of bond angles. The sum of bond numbers at a given atom is roughly constant and does not depend on the environment. “Standard bond lengths” of a fragment are determined by a least-squares procedure based on all available data. They are supplemented by curves that describe the observed distortions.
The shape of these correlation curves is reminiscent of the structural changes occurring along the pathways of chemical reactions, e.g. nucleophilic substitution at tetrahedrally coordinated atoms (SN1 and SN2), nucleophilic addition to carbonyl groups, electrocyclic ring closure of polyenes, pseudo-rotation of five-membered rings or Berry pseudo-rotation. For many of these reactions approximate energy hypersurfaces have been obtained from quantum mechanical calculations, model force fields and from spectroscopic information (IR, NMR). Comparison between reaction pathways determined from structural correlations with those obtained from models of the energy surfaces shows fair agreement.
TL;DR: In this article, the syntheses, properties, and applications of new optical brighteners are described with references to patent literature, and they are used in detergents, textiles, paper, plastics, and paints.
Abstract: Optical brighteners are used in detergents, textiles, paper, plastics, and paints. Most optical brighteners contain heterocycles such as coumarins, 2-pyrazolines, naphthalimides, pyrazoles, triazoles, oxadiazoles, and triazines. In this article the syntheses, properties, and applications of new optical brighteners are described with references to patent literature.
TL;DR: In this paper, a method of preparing masked α-secondary amino carbanions consists in nitrosation of the secondary amine, followed by metalation of resulting nitrosamine α-to the nitrogen, reaction with electrophiles, and subsequent denitrosation.
Abstract: There are basically two kinds of hetero atoms in organic molecules: one kind confers electrophilic character upon the carbon atom to which it is bound, and the other kind turns it into a nucleophilic site. The development of methods permitting transitions between the two resulting categories of reagents has become an important task of modern organic synthesis. The scope of such umpolung of the reactivity of functional groups is discussed for the case of amines as an example. A method of preparing masked α-secondary amino carbanions consists in nitrosation of the secondary amine, followed by metalation of the resulting nitrosamine α-to the nitrogen, reaction with electrophiles, and subsequent denitrosation. Many examples are given for each of these steps which illustrate the wide scope of the overall synthetic operation (electrophilic substitution at the α-C atom of the secondary amine). Preliminary applications and a method for avoiding the handling of nitrosamines are presented, and the report concludes with a brief account of the significance of nitrosamines in the study of carcinogenesis and mutagenesis.
TL;DR: The types of sulfur bonding that occur in the molecules of maingroup elements are almost unknown in the chemistry of metal complexes, where the sulfur atoms function instead as two-electron donors as discussed by the authors.
Abstract: The types of sulfur bonding—as sulfane or sulfide—encountered in the molecules of maingroup elements are almost unknown in the chemistry of metal complexes, where the sulfur atoms function instead as two-electron donors by bridging two metal atoms, as four-electron donors by bridging three or four metal atoms, or as six-electron donors by incorporation between four metal atoms. In such complexes, the metal-metal bond can be modified over a wide range by chemical or electrochemical variation of the number of electrons present. The readiness with which polynuclear complexes containing metals and sulfur undergo redox reactions is also utilized by Nature in the active sites of some redox proteins.
TL;DR: Field desorption (FD) enables mass-spectrometric investigation of large organic molecules without their vaporization as discussed by the authors, and is particularly suitable for the detection and identification of sub-microgram quantities of underivatized polar substances present in complex mixtures or pre-purified extracts from biological materials.
Abstract: Field desorption (FD) enables mass-spectrometric investigation of large organic molecules without their vaporization. The present state of our theoretical understanding of the ionization of these molecules in the adsorbed state on organic emitters is described. The special problems of the technique and prospective developments in the apparatus for future analytical problems are outlined. The present progress report concentrates on analytical studies of biochemical model compounds and degradation products from environmental chemicals and drugs. The method is particularly suitable for the detection and identification of submicrogram quantities of underivatized polar substances present in complex mixtures or pre-purified extracts from biological materials.
TL;DR: In this article, SS-Valenzschwingungen konnen im Bereich 177-820 cm-' auftreten, und Kraftkonstanten von 1.4 bis 6.3 mdyn/A wurden berechnet.
Abstract: SS-Bindungen sind aufiergewohnlich flexibel und haben Eigenschaften, die bei anderen homonuclearen Bindungen bisher nur vereinzelt beobachtet wurden : die Kernabstande variieren zwischen 1.8 und 3.0 A, die Valenzwinkel zwischen 90 und 180", die Diederwinkel zwischen 0 und 180", und die Bindungsenergien reichen bis 430 kJ/mol. SS-Valenzschwingungen konnen im Bereich 177-820 cm-' auftreten, und Kraftkonstanten von 1.4 bis 6.3 mdyn/A wurden berechnet. Diese Vielfalt wird an Beispielen mit isolierten und kumulierten SS-Bindungen erlautert.
TL;DR: In this paper, anwendungen und ein Verfahren zur Umgehung des Hantierens von Nitrosaminen werden vorgestellt, and zum Schlus wird die Bedeutung der Nitrosamine fur die Carcinogenese-and Mutageneseforschung kurz erortert.
Abstract: Es gibt prinzipiell zwei Arten von Heteroatomen in organischen Molekulen: Die einen machen das mit ihnen verbundene Kohlenstoffatom zu einem elektrophilen, die anderen zu einem nucleophilen Zentrum. Die Entwicklung von Methoden zum Uberwechseln zwischen den beiden darauf beruhenden Kategorien von Reagentien ist eine wichtige Aufgabe der modernen organischen Synthese. Moglichkeiten dieser Umpolung der Reaktivitat funktioneller Gruppen werden am Beispiel der Amine diskutiert. Eine Methode zur Herstellung von maskierten α-sek.-Aminocarbanionen besteht darin, das man das sekundare Amin nitrosiert, das entstandene Nitrosamin in α-Stellung zum Stickstoff metalliert, mit Elektrophilen umsetzt und entnitrosiert. Fur jeden dieser Schritte wird eine Anzahl von Beispielen gegeben, die die grose Anwendungsbreite der synthetischen Gesamtoperation (elektrophile Substitution am α-C-Atom des sekundaren Amins) belegen. Erste Anwendungen und ein Verfahren zur Umgehung des Hantierens von Nitrosaminen werden vorgestellt, und zum Schlus wird die Bedeutung der Nitrosamine fur die Carcinogenese- und Mutageneseforschung kurz erortert.
TL;DR: In this paper, the dreidimensionale bau von haufig vorkommenden Molekulfragmenten wurde systematisch untersucht, so etwa von Wasserstoffbrucken, OH…O, Trijodid-Ionen, J, and and other linearen dreiatomigen Fragmenten, von tetraedrischen Ionen w.r.t.
Abstract: Der dreidimensionale Bau von haufig vorkommenden Molekulfragmenten wurde systematisch untersucht, so etwa von Wasserstoffbrucken, OH…O, Trijodid-Ionen, J, und anderen linearen dreiatomigen Fragmenten, von tetraedrischen Ionen wie SO42−, PO43−, AlCl4− und verwandten Spezies, von Keto- und Aminogruppen, die zusammen im gleichen Molekul vorkommen, von substituierten [10]Annulenen und Cycloheptatrienen, von organischen Funfringverbindungen sowie von pentakoordinierten Metall- oder Nichtmetallatomen. Die Bindungsabstande und -winkel, welche die Struktur eines solchen Fragments beschreiben, erstrecken sich uber Bereiche, die ein Vielfaches der experimentell bedingten Standardabweichung einer Einzelmessung ausmachen. Die verschiedenen geometrischen Strukturparameter eines Fragmentes sind voneinander abhangig, und ihre Korrelation kann mit der Paulingschen Beziehung zwischen Abstanden r und Bindungsordnungen n, r = r0 − c log n, beschrieben werden, wenn n ebenfalls als Funktion von Strukturparametern, vor allem von Winkeln, ausgedruckt wird. Die Summe der Bindungsordnungen n ist um jedes Atom ungefahr konstant und unabhangig von der genauen Struktur der Umgebung, „Standardbindungslangen” eines Fragmentes werden aus allen vorhandenen Daten durch Ausgleichsrechnung bestimmt und erganzt durch Kurven, die bevorzugte Abweichungen von der „Standardstruktur” wiedergeben. Der Verlauf solcher Korrelationskurven erinnert an Reaktionswege minimaler Energie, soweit sie das strukturelle Geschehen wahrend der nucleophilen Substitutionen (SN1 und SN2), der nucleophilen Addition an Carbonylgruppen, der elektrocyclischen, disrotatorischen Ringschlusreaktion von Polyenen, der Pseudorotation von Funfringverbindungen und des Berry-Mechanismus beschreiben. Fur viele dieser Reaktionen sind ungefahre Energiehyperflachen und Reaktionswege aus quantenmechanischen Rechnungen, Kraftfeldmodellen oder aus Interpretationen spektroskopischer Messung (IR und NMR) bestimmt worden. Die aus Strukturkorrelationen bestimmten Reaktionswege werden mit denen, die aus Modellrechnungen stammen, verglichen und stimmen mit ihnen uberein.
TL;DR: In this paper, the versatility of vinyl azides in organic reactions is demonstrated, showing that the reactive azide function is susceptible to thermolysis, photolysis, cycloadditions, and attack by nucleophiles and electrophiles.
Abstract: This review is designed to demonstrate the versatility of vinyl azides in organic reactions. The reactive azide function is susceptible to thermolysis, photolysis, cycloadditions, and attack by nucleophiles and electrophiles. The neighboring double bond accentuates the reactivity of the azide function and provides additional intramolecular pathways for reaction. Last but not least, the presence of an appreciable electron density at the β-vinyl carbon makes this class of compounds comparable with enamines in their reactions with electrophiles and 1,3-dipoles.
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TL;DR: In this paper, the main features of the generation of aminyl free radicals, their reactivity, and electronic properties are reviewed, and a detailed review of their properties is presented.
Abstract: Recent interest in aminyl free radicals, especially in their electronic structure, has led to many investigations in this area. This report reviews the main features of the generation of aminyls, their reactivity, and electronic properties.
TL;DR: In the past 25 years a new branch of research has developed under the name "stable isotope geochemistry" and its importance within the earth sciences has steadily increased as discussed by the authors, and the present progress report considers the scope and also the limitations, of this discipline.
Abstract: During the past 25 years a new branch of research has developed under the name “stable isotope geochemistry”, and its importance within the earth sciences has steadily increased. The present progress report considers the scope, and also the limitations, of this discipline.
TL;DR: Partial and total syntheses of tetracyclines are described, the influence of electronic, steric, and lipophilic factors and of complex formation on biological activity are discussed, and problems involved in the development of resistance are discussed.
Abstract: Tetracycline antibiotics continue to play an important role in human and veterinary medicine and in animal nutrition. The classical tetracyclines obtained by fermentation have been supplemented by products of partial synthesis which provide, in particular, the advantages of better pharmacokinetic properties and greater tolerance. Following a brief review of older work, the present article describes partial and total syntheses of tetracyclines, the influence of electronic, steric, and lipophilic factors and of complex formation on biological activity. The inhibition of biochemical systems invoked in interpretation of the mode of action of tetracyclines and problems involved in the development of resistance are discussed.
TL;DR: In this paper, a difference Fourier synthesis through the best plane (k 0.02 A) of the thiadiborolene ring was performed, and the Fourier coefficients were obtained on refinement of all atoms except hydrogen with 1468 reflections.
Abstract: The bond lengths in the ring system unequivocally establish the fixation of the. x-electron system as cyclohexatriene with formation of a long. K bond to the iron. Figure 2 shows a difference Fourier synthesis through the best plane (k0.02 A) of the thiadiborolene ring; the Fourier coefficients were obtained on refinement of all atoms except hydrogen with 1468 reflections (sin O/h = 0.5, R = 0.0305, h,, = 0.71069 b;) The 7s-electron densities accord with the bond lengths found. The appearance of K-electron density in the B1-C4 and B2-C9 bonds warrants particular attention. The relatively long B-S bonds (1.874 A) exceed those in trithiaborolane~[~] (1 303 A) and thiaborins[81 (1.807 8). Expectedly, a CO group on the iron is positioned trans to the sulfur.