bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthese und Kristallstruktur von Tetramethylammonium‐Sodalith
Authors: Baerlocher Ch. , Meier W. M. 
Published: December 2004

AbstractTetramethylammonium sodalite, a synthetic species of composition (CH3)4NAlSi5O12, has been obtained in good yield under hydrothermal conditions in the absence of metal cations. Its crystal structure has been determined using accurate powder data since single crystals could not be grown. The structure seems to be body‐centered cubic with a = 8.975 Å but the true symmetry is non‐cubic (probable space group I4). Each cage of the aluminosilicate framework contains one tetramethylammonium ion. The organic cation does not conform to the cubic symmetry of the ideal framework. The methyl groups point to oxygen atoms of the framework, and the short methyl‐oxygen distances of 3.06 Å indicate strong CH … O interaction.The present results indicate beyond doubt that CH … O hydrogen bonding involving methyl groups can occur in silicates. This is of particular significance in zeolite chemistry and in the interpretation of interlayer distances in organic clay complexes.
Die Konstitution der Melodinus‐Alkaloide (+)‐Meloscin, (+)‐Epimeloscin und (+)‐Scandin. 1. Mitteilung über Alkaloide aus Melodinus scandens FORST
Authors: Bernauer Karl , Englert G. , Vetter W. , Weiss Ek. 
Published: December 2004

AbstractFor the alkaloids meloscine, epimeloscine and scandine, isolated from the Apocynacee Melodinus scandens FORST., the structures 1, 10 and 11, respectively, are deduced. Scandine is proved to possess the relative configuration as shown in 11 r. For meloscine and epimeloscine the relative configurations as depicted in 1 r and 10 r are discussed.
ESR‐Spektren von CuN4‐Chromophoren II: Komplexe mit Ammoniak, Äthylendiamin, Biguanid, N‐Trifluoracetimidoyl‐trifluoracetamidin, N‐Trichloracetimidoyl‐trichloracetamidin, Tetraaza‐undecan, Hexamethyl‐tetraaza‐cyclotetradecan und ‐cyclotetra decadien in Einkristallen
Authors: Schneider W. , Baccini P. 
Published: December 2004

AbstractThe ESR spectra of eight copper complexes with two groups of nitrogen ligands have been measured in the solid state. The first group includes the σ‐bonding ligands ammonia, ethylenediamine, 1,4,8,11‐tetraaza‐undecane, and the macrocyclic hexamethyl‐1,4,8,11‐tetraazacyclotetradecane of CURTIS. Ligands of the second group are biguanide, the CF3 and CCl3 derivatives of acetimidoyl‐acetamidine, and hexamethyl‐1, 4,8,11‐tetraazacyclotetradecadiene.Single crystals of the parent PtII, NiII, or ZnII compounds were used as host lattices and magnetic diluents. The spectra of the chromophores CuN4, showing resolved hyperfine structure due to copper and nitrogen nuclear spins, are fitting a Spin‐Hamiltonian on the basis of virtual site symmetry D4h. The parameters g∥, g⟂, A∥, and A⟂ were used to derive delocalization coefficients in terms of the LCAO‐MO model introduced by MAKI and MCGARVEY. The comparative study clearly reveals that no reliable information on π‐bonding is provided by application of this model. The results on σ‐bonding ligands are particularly valuable in showing that the simple LCAO‐MO model cannot account for the attenuation of spin orbit coupling due to σ‐bonding in a physically meaningful way. Our results are qualitatively in agreement with AMMETER'S explanation of this phenomenon in terms of a virtual expansion of the d‐shell in antibonding orbitals.
Koordinationszahl und nephelauxetischer Effekt von Komplexen der Lanthaniden
Authors: Geier G. , Karlen U. , v. Zelewsky A. 
Published: December 2004

AbstractThe EuIIIEDTA complex exhibits a strong temperature dependence of its absorption band at 395 nm in dilute aqueous solution. Similar but much weaker effects can be observed in solutions of SmEDTA and GdEDTA, whereas EDTA complexes of the other lanthanide ions as well as the aquo ions of the whole series show no significant change of their absorption spectra in nation number along the series of the lanthanide EDTA complexes that takes place from Sm to Tb at room temperature. It can be concluded from the nephelauxetic effect that the coordination number decreases with increasing atomic number. The coordination numbers of the aquo ions are the same for all trivalent lanthanide ions in dilute solutions.
Allgemeine Säure‐Basen‐Katalyse der Monomethylol‐Bildung aus Harnstoff und Formaldehyd in Wasser
Authors: Glutz B. R. , Zollinger H. 
Published: December 2004

Abstract
The kinetics of the reaction of formaldehyde with urea in aqueous solutions was studied polarographically between pH 0.99 and 12.45 at 40°C.
The reaction is first order with respect to both reactants and is subject to general acid and base catalyses. The catalytic constants for 21 catalysts were determined.
The catalytic constants follow, in general, the BRÖNSTED relationship to the acidity and basicity constants, respectively, of the catalysts.
It is emphasized that, in contrast to recent statements by PETERSEN, mechanisms involving a series of bimolecular steps involving acid‐base pre‐equilibria or rate‐limiting proton transfers are incompatible with the experimental data. In the rate‐limiting transition state urea, formaldehyde, and the catalyst are present.
At pH‐values above 11, the CANNIZZARO reaction is competitive with the methylol formation.
Höhere, kondensierte Ringsysteme. 4. Mitteilung. Grosse Ringe der [2n]Metacyclophanreihe
Authors: Paioni R. , Jenny W. 
Published: December 2004

Abstract[27] Metacyclophane, [29] metacyclophane, and [210] metacyclophane with a 50‐membered ring are isolated in the pure state from the crude product of a WURTZ reaction with m‐xylylene dibromide, thus providing for the first time a complete series of cyclophanes with two to ten sub‐units. The structure of the new ring systems is determined from their UV., IR., NMR. and mass spectra. The physical constants of these large carbocyclic systems are compared with those of the well‐known smaller metacyclophanes, particularly with respect to conformation.
Strahlungschemie von Kohlenwasserstoffen. 16. Mitteilung. Benzol‐Brombenzol
Authors: Siegrist Renato , Gämann Tino 
Published: December 2004

AbstractThe decrease of the concentration of bromobenzene and the formation of biphenyl and bromobiphenyl have been studied in the system benzene‐bromobenzene under the influence of γ‐rays. Bromobenzene is in competition with its own products for the reactive state of benzene or it can transfer its energy to its products. The rate of this transfer to decomposition is 74 l/Mol. With the help of additives it has been shown that they can act in two ways: firstly they compete with bromobenzene for an activated state of benzene in a reaction that does not depend on temperature. The nature of this activated state has not been determined. Secondly they scavenge phenyl radicals that have been formed in about 70% of the decomposed bromobenzene molecules. This yield depends slightly on temperature. The relative reactivities compared to bromobenzene for the first case and to benzene in the second have been determined as follows: naphthalene (0.6; 23); anthracene (5.8; 800); benzophenone (0.5; 17); cyclohexene (‐; 20); N2O (0.018; ‐); NO (1.7; 250); O2 (‐; 3400). Naphthacene in benzene is strongly decomposed in the presence of bromobenzene, but it also enhances the decomposition of the latter.
Katalyse der Reaktion von Thionylchlorid mit Trichloressigsäure
Authors: Konecny Jan 
Published: December 2004

AbstractThe reaction of thionyl chloride with trichloroacetic acid is catalyzed by tetraethylammonium chloride, and the rate is proportional to the concentration of the salt. The catalytic activities of tetraethylammonium chloride, pyridine hydrochloride and piperidine hydrochloride are in the ratio 1: 0.4: 0.3.
Etude phosphorimétrique des complexes de l'acide borique avec la benzoylacétone dans des glaces d'«éther diéthylique‐acide sulfurique concentré» à 77K
Authors: Marcantonatos M. , Gamba G. , Monnier D. 
Published: December 2004

AbstractBoric acid‐benzoylacetone complexes, formed in concentrated sulfuric acid, are investigated phosphorimetrically after addition of ether to forme suitable glaces at 77K. Spectral, equilibrium and mean lifetime determinations establish the formation of two successif mononuclear complexes of stability β1 = 1.4 ± 0.1 ± 105 et β2 = 3.1 ± 0.3 ± 107. Structures, based on equilibrium and spectral data, are proposed. The applicability of phosphorimetry to complex formation studies and its advantages, in this case, over fluorimetry and colorimetry, are briefly discussed on the basis of results obtained in the present work.
Etudes sur les composés organométalliques. XI [1]. Action du tétrabutoxytitane sur des solutions de Grignard
Authors: Dubsky George Jon , Jacot‐Guillarmod André 
Published: December 2004

AbstractThe reaction of titanium tetra‐n‐butoxide with phenylmagnesium bromide inether has been investigated. The species (C6H5)2Mg in the Grignard reagent leads to (C6H5)4Ti, whereas the dimeric species (C6H5)2Mg · MgBr2 produces an insoluble complex mTi(OBu)4 · n[(C6H5)2Mg · MgBr2]. Applied to other Grignard reagents, the use of R2Mg allowed the preparation of tetrabenzyltitanium, tetracyclohexyltitanium and tetramethyltitanium. Cristalline (C6H5)4Ti and (C6H5CH2)4 Ti have been isolated.
Darstellung und Eigenschaften von Komplexen des Typs cis‐(RCN)3M(CO)3 (M = Cr, M, W)
Authors: Werner H. , Deckelmann K. , Schönenberger U. 
Published: December 2004

AbstractMetal complexes of the type cis‐(RCN)3M(CO)3 (M = Cr, Mo, W) have been prepared by different methods starting with M(CO)6 or, more conveniently, with substituted derivatives of the metal hexacarbonyls. Infrared spectroscopic studies indicate that the strength of the nitrile‐to‐metal bond in cis‐(RCN)3M(CO)3 is only sligthly influenced by the R group. The chromium compounds cis‐(RCN)3Cr(CO)3 may be used as starting materials for the preparation of hexaalkylborazine‐chromium‐tricarbonyls.
Etude par spectrométrie de masse de l'ionisation de benzonitriles, de phénylacétonitriles et de N,N‐diméthylanilines substitués
Authors: Buchs Armand 
Published: December 2004

AbstractMolecular ionization potentials for series of compounds of the type XC6H4CN, XC6H4CH2CN and XC6H4N(CH3)2 have been measured using the retarding potential difference technique (RPD. technique). The effect of the various substituents X is better correlated through the electrophilic Brown σp+ constants than through Hammett's σp values. No meta‐para orientation effect is observed. For all the disubstituted phenyl compounds studied, the effect of the second substituent is affected by the electron‐releasing power of the original substituent. Ionization potentials calculated by using the semi‐empirical method of equivalent orbitals are in good agreement with the experimental values.
Photochemische Umwandlungen. XXXVIII [1]. Synthese und Eigenschaften Methoxycarbonyl‐substituierter «Quadricyclanone»
Authors: Prinzbach H. , Rivier J. , Englert G. 
Published: December 2004

AbstractThe three methoxycarbonyl‐substituted quadricyclanones 7a, 7b and 7c have been synthesized in good to excellent yields. Some of their physical (UV., NMR.) and chemical properties (e.g. condensation and pyrolysis reactions) are discussed.
Steroide und Sexualhormone. 238. Mitteilung [1]. Die Synthese von 14βO, 18N‐Ep (oxyäthanoimino)‐Steroiden
Authors: Berner‐Fenz Frau L. , Berner H. , Graf W. , Wehrli H. 
Published: December 2004

AbstractThe synthesis of the title compound 3 is described. The reaction sequence will serve as a model for a partial synthesis of batrachotoxinin A (2).
Steroide und Sexualhormone. 240. Mitteilung [1]. Die Synthese von 3β‐Methoxy‐3α, 9α‐oxido‐11α,20ξ‐dihydroxy‐14βO,18N‐[ep(oxyäthano‐N‐methylimino)]‐5β,17α‐pregnan (3‐O‐Methyl‐17α,20ξ‐tetrahydrobatrachotoxinin A)
Authors: Graf W. , Berner H. , Berner‐Fenz Frau L. , Gössinger Frl. E. , Imhof R. , Wehrli H. 
Published: December 2004

AbstractThe synthesis of 3‐O‐methyl‐17α, 20ξ‐tetrahydrobatrachotoxinin A (4) is described.
Über die Bildung von 9‐Hydroxy‐10,12‐ und 13‐Hydroxy‐9,11‐octadecadiensäure durch «Lipoperoxidase» aus Cerealien. Vorläufige Mitteilung
Authors: Heimann W. , Schreier P. 
Published: December 2004

AbstractNach Inkubation der durch Soja‐Lipoxygenase (E. C. 1. 13. 1. 13) gebildeten Linolsäurehydroperoxide (LHPO) mit einem Hafer‐Acetontrockenpulver in Phosphatpuffer pH 7,0 (0,05M) wurden als Umsetzungsprodukte die beiden ungesättigten 9‐Hydroxy‐10, 12‐ und 13‐Hydroxy‐9, 11‐octadecadiensäuren erhalten. Diese Reaktion wurde durch Einsatz von radioaktiv markierten LHPO bestätigt. Nach vorheriger Hitzeinaktivierung blieb die Umsetzung aus. Die Identifizierung der Reaktionsprodukte erfolgte an Hand der Massenspektren nach Veresterung, katalytischer Hydrierung und Oxydation zu 9‐Oxo‐ bzw. 13‐Oxo‐stearinsäure‐methylester.
Crystal Structure of the Antibiotic Monensin Similarities and Differences between Free Acid and Metal Complex
Authors: Lutz W. K. , Winkler F. K. , Dunitz J. D. 
Published: December 2004

AbstractThe structure of monensin, C36H62O11, has been determined by X‐ray analysis of its crystalline monohydrate (orthorhombic, a = 15.15, b = 23.61, c = 10.65 Å, Z= 4, space group P212121). Phases were assigned by direct methods, making use of the ‘tangent formula’. Although the conformation of the free acid resembles that of the silver salt in being cyclic, there are differences in the hydrogen bonding pattern. These features are discussed in relation to the complexation of metal ions by monensin.
Über Oxidhydroxide des vierwertigen Mangans mit Schichtengitter. 3. Mitteilung. Reduktion von Mangan(III)‐manganat(IV) mit Zimtalkohol
Authors: Giovanoli R. , Feitknecht W. , Fischer F. 
Published: December 2004

AbstractManganese(III) manganate(IV), one of the synthetic varieties of the birnessite group, is readily reduced in xylene suspension by cinnamyl alcohol. At moderate temperatures, including room temperature, γ‐MnOOH (manganite) forms topotactically in extremely thin needles and is therefore easily overlooked in the X‐ray examination. At higher temperatures further reduction occurs (MnIII → MnII), and Mn3O4 (hausmannite) appears in comparatively large, equant cristallites which are less distinctly oriented. For comparison Na4Mn14O27, 9H2O, which has also been investigated, is much more stable than Mn7O13, 5H2O. The same holds for finely divided synthetic varieties of the birnessite group precipitated from KMnO4 solutions; by their behaviour they are related to Na4Mn14O27, 9H2O rather than to Mn7O13, 5 H2O which is consistent with their substantial alkaline ion content.These results raise the question: is the so‐called ‘todorokite’ a pure crystal species. According to present data ‘todorokite’ could be regarded as a transition product, i.e. as half decomposed buserite admixed with birnessite and substantial amounts of manganite.
Etude de composés d'addition d'acides de Lewis XXXIII [1]. Résonance magnétique nucléaire de composés formés par des aldéhydes aliphatiques et aromatiques avec des accepteurs électroniques
Authors: Filippini Franchino , Susz B.‐P. 
Published: December 2004

AbstractComplétant leur étude des spectres d'absorption IR. de composés d'addition d'aldéhydes avec des acides de Lewis, montrant que l'accepteur se fixe sur l'atome d'oxygène du groupe CHO, avec diminution du caractère de double liaison de CO, les auteurs ont enregistré le spectre de RMN. protonique de certains de ces composés, en solution 0,2M dans CH2Cl2. Pour les aldéhydes aliphatiques, la variation Δτ du déplacement chimique de l'atome H de CHO due à l'addition de l'accepteur est négative et de l'ordre de grandeur de −0,1 à−0,4 ppm, ce qui correspond à un certain déplacement électronique dans la direction H → C → O, particulièrement marqué pour Cl3CCHO · SbCl5 (δτ = −0,41 ppm). Pour le benzaldéhyde, en revanche, Δτ est plus proche de zéro ou même positif: le noyau aromatique forme réservoir d'électrons modérant le déplacement cité. En tenant compte encore de variations éventuelles des effects d'anisotropie du noyau aromatique et du groupe CO donneur, on peut expliquer les valeurs observées.
The Structures of Medium‐Ring Compounds. Part XVII. Crystal and molecular structures of cis‐cyclodecene. 1/2 AgNO3 and 1,1,4,4‐tetramethyl‐cis‐cyclodec‐7‐ene. 1/2 AgNO3
Authors: Ermer O. , Eser H. , Dunitz J. D. 
Published: December 2004

AbstractThe crystal structures of cis‐cyclodecene. 1/2 AgNO3 (monoclinic, a = 5.329, b=14.53, c=27.17 Å, β=92.02°, space group C 2/c) and of 1,1,4,4‐tetramethyl‐cis‐cyclodec‐7‐ene · 1/2 AgNO3 (orthorhombic, a=5.879, b=16.86, c=28.39 Å, space group C2221) have been determined. The relative arrangement of Ag+ cations, NO3− anions and cyclo‐olefin molecules are very similar in the two crystals, but the conformations of the ring skeletons are very different.
Structure of [4.4.4]propellane and [4.4.4]propellatriene by X‐ray Analysis
Authors: Ermer O. , Gerdil R. , Dunitz J. D. 
Published: December 2004

AbstractThe crystal structures of [4.4.4]propellane (monoclinic, a=12.053, b=7.832, c=13.001 Å, β=104.89°, space group C2/c, Z=4) and [4.4.4]propellatriene (monoclinic, a=7.876, b=12.651, c=13.164 Å, β=122.81°, space group P21/c,Z=4) have been determined by X‐ray analysis. In propellane the six‐membered rings are in the chair conformation, in propellatriene they adopt the ‘half‐chair’ conformation with a twofold axis passing through the centre of each double bond. In both cases the observed parameters correspond to virtual D3(32) molecular symmetry. Corrections have been applied for the effect of molecular libration. Strain‐minimization calculations based on semi‐empirical potential functions have been carried out and the molecular parameters so derived are compared with the experimental values.
Steroid Total Synthesis, Part III. 9β, 10α‐Testosterone
Authors: Saucy G. , Borer R. 
Published: December 2004

AbstractThe total synthesis of 9β, 10α‐testosterone via a BCD‐tricyclic intermediate is described. The latter compound – 17β‐hydroxy‐des‐A‐androst‐9‐en‐5‐one – was obtained in optically active form by our previously reported scheme, using an efficient resolution step early in the synthesis. New results regarding the asymmetric induction step are also discussed.
Composés d'addition des halogénures de niobium(V) et de tantale(V) IV. Stabilité relative des composés de chlorures avec quelques nitriles
Authors: Merbach A. , Bünzli J. C. 
Published: December 2004

AbstractThe relative stability constants of the adducts of MCl5 (M  Nb, Ta) with acetonitrile, halogenoacetonitriles, pivalonitrile, acrylonitrile and benzonitriles are determined in dilute solutions by NMR. methods. The stability of the adducts is controlled by inductive factors. Chemical shifts and analysis of the new compounds are reported.
Röntgen‐Kontrastmittel: (2,4,6‐Trijodbenzoyl)‐aminosäuren
Authors: Suter H. , Zutter H. 
Published: December 2004

AbstractNew N‐(3, 5 substituted 2,4,6‐triiodobenzoyl)‐amino acids have been synthesized as potential X‐ray contrast agents for chloecystography. Toxicity, bilitropism, urotropism, and cholecystographic quality of these compounds are given.
Photochemische Umwandlungen, 45. Mitteilung [1] die 3σ → 3π‐route zu oxepin‐derivaten
Authors: Eberbach W. , Perroud‐Argüelles M. , Achenbach H. , Druckrey E. , Prinzbach H. 
Published: December 2004

AbstractExemplifying with the 4.5‐dicarbomethoxy oxepin 6a the authors describe an oxepin synthesis from furanes and acetylenic dienophiles via Diels‐Alder reaction (4a), photochemical oxanorbornadiene‐oxaquadricyclane transformation (4a → 5a), and thermal 3σ → 3π opening of the highly strained oxaquadricyclane 5a. With dimethylacetylenedicarboxylate, methylpropiolate, maleic anhydride, and di‐methoxycarbonyl‐oxanorbornadiene (4a) 5a yields the 1:1 adducts 19a, 19b, 22, 23 and 26 (unstable) by strictly stereospecific addition to the α‐positions of the oxygen bridge. With the same dienophiles the oxepin 6a reacts only through its valence‐tautomeric benzene‐oxide form 7a giving stereospecifically 27, 29, 30 and 31. No definite conclusions are drawn with regard to the mechanistic implications of the photostep 4a → 5a, the thermal 3σ → 3π‐transformation 5a → 6a/7a, and the bishomofurane cycloaddition reactions. Scope and limitations of this oxepin synthesis are briefly discussed.
Equilibres conformationnels de glucides au niveau de liaisons σ sp2‐sp3 C‐C. III Dérivés d'oximes d'aldéhydo‐sucres utilisation de tris‐dipivaloylméthanato‐europium
Authors: Tronchet J. M. J. , Barbalat‐Rey F. , Le‐Hong N. 
Published: December 2004

AbstractA series of sugar oximes and O‐methyloximes of the general formula RCHNOR′ (R′  H, CH3) have been studied by PMR. spectroscopy. These compounds exist in solution as a mixture of the syn and anti isomers. The conformational equilibrium of the syn isomers seems to consist exclusively of the eclipsed rotamers, whereas for the anti isomers there appears to be a significant contribution from bisecting rotamers. Using tris‐dipivaloylmethanato‐europium it is found that the α proton of the anti oximes is much more deshielded than the corresponding proton of the syn isomers, which means that the downfield shift of a particular proton does not depend exclusively on its distance from the oxygen of the oxyimino group.
Substituierte 9‐Oxabicyclo[4.2.1]‐ und 9‐Oxabicyclo[3.3.1]nonane III. neue ergiebige synthese von 2, 7‐dioxatwistan und endo‐2‐hydroxy‐9‐oxabicyclo[3.3.1]nonen‐(6)
Authors: Ganter C. , Zwahlen W. 
Published: December 2004

AbstractIodine cleavage of the [3.3.1]‐iodomercuri compound 4, easily prepared from cis, cis‐cyclooctadiene‐(1,5) by oxymercuration of the monoepoxide 1 (→ 3) followed by treatment with potassium iodide, leads to three isomeric iodides 6, 7, and 8, the [3.3.1]‐exo‐iodo isomer 8 being the predominant product.Intramolecular substitution in 8 opens an attractive new route to unsubstituted 2,7‐dioxatwistane (19) [2], whereas dehydrohalogenation of 7 and 8 yields the unsaturated alcohol 17 [2], a suitable starting material for the preparation of substituted 2,7‐dioxatwistanes [2], 2,7‐dioxaisotwistanes (e) [2], and 2,8‐dioxa‐homotwistbrendanes (f).
Über den Verteilungssatz der Auxochrome bei Azokörpern IV Azokörper mit zueinander p‐ständigen Auxochromen
Authors: Kokkinos K. , Wizinger R. 
Published: December 2004

AbstractIn azo compounds with CH3O groups in o‐position to the azo groups the introduction of the weak auxochromes CH3– and CH3O– into the p‐position to the methoxy group (m‐position to the chromophor) causes relatively strong bathochromic effects, in conformity with the rule of repartition.
Die Synthese von überbrückten Cobaloximen
Authors: Rétey J. 
Published: December 2004

AbstractChloro‐pyridino‐bis (glyoximato)‐cobalt(III) complexes (cobaloximes) have been synthesized in which two corners are connected by a bridge consisting of 10 or 12 methylene groups. These compounds are designed to mimic some important features of the active site of coenzyme B12 dependent enzymes.
X‐Ray Analysis of a Bridged Cobaloxime (Chloro‐pyridino‐cis‐ 1,12‐bis‐methyglyoximato‐dodecane‐cobalt(III))
Authors: Bartlett M. W. , Dunitz J. D. 
Published: December 2004

AbstractThe structure of the title compound, a cobaloxime bridged by a polymethylene chain, has been confirmed by X‐ray analysis.
Protonierungs‐ und Deprotonierungskinetik des Systems Azulen‐Azuleniumkation, ein Beitrag zur Kenntnis der Hammett'schen Ho‐Aciditätsfunktion
Authors: Seiler P. , Werthemann D. 
Published: December 2004

AbstractUsing a flashphotolysis‐method to evaluate the rates of the protonation of azulene and the deprotonation of azuleniumcation as a function of H0 the validity of the Hammett H0‐function was examined. Using this technique it was possible to obtain information on the behaviour of the activity coefficients and to show that the Hc‐acidityfunction of Reagan [1] is a better measure of the hydrogen activity than the H0‐function. The dependence of the deprotonation rate on H0 is explained as a consequence of the different behaviour of the activity coefficients of Hammett‐indicators and azulene/azuleniumcation, respectively.