bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulphur Analogues of Deoxyvasicinone
Authors: Dunn A. D. , Norrie R.
Published: December 2004

The synthesis of the 2‐thioanalogue of deoxyvasicinone (1) 5 and some higher analogues 6 and 7 are described. Oxidation of these heterocycles with 3‐chloroperoxybenzoic acid gave the sulphoxides 12, 13 and 14 which underwent facile Pummerer rearrangement to yield, after deacetylation, the alkanols 18, 19 and 20. Under more vigorous oxidising conditions 5 and 6 were oxidatively ring opened to yield the sulphonic acids 21 and 22 whereas 7 gave the sulphone 23.
Untersuchungen zur Iodierung von 4‐Amino‐2,6‐dimethyl‐pyrimidinen – eine Möglichkeit zur regiospezifischen Funktionalisierung
Authors: Niclas H.‐J. , Zeuner F. , Gründemann E. , Zölch L.
Published: December 2004

Studies on the Iodination of 4‐Amino‐2,6‐dimethylpyrimidine — A Possibility of the Regiospecific Functionalization

The iodination of 4‐amino‐2,6‐dimethyl‐pyrimidine 1a with I2/H2SO4/H2O/H2O2 does not give, as supposed hitherto, the 5‐iodo derivative (2) but affords the corresponding 2‐iodomethyl derivative 3a. The reaction pathway of the iodination is discussed. The reaction of 3a with nucleophiles leads to a variety of side chain‐substituted pyrimidines 5a–j.
Kinetics and regioselectivity of the Autoxidation of o‐Substituted Isopropyl Aromatics
Authors: Heinze Antje , Lauterbach Gerlinde , Pritzkow Wilhelm , Schmidt‐renner Wolfgang , Voerckel Volkmar , Zewegsuren Nansadyn
Published: December 2004

The relative chain propagation constants and the regioselectivities of the oxidations of o‐cymene and 2‐isopropyl‐1,4‐dimethylbenzene were determined by competitive oxidations of the hydrocarbons with cumene. As expected, the reactivity of the tertiary CH bond of the isopropyl group is considerably decreased by o‐methyl groups.

Also in α‐isopropylnaphthalene a considerable decrease in the reactivity of the tertiary CH bond takes place.

The decrease of the chain propagation constants effects a decrease of the oxidabilities of o‐substituted isopropyl aromatics. In the case of the methyl isopropyl benzenes the increase of the chain termination constants by primary peroxy radicals must also be taken into consideration. This results in a decrease of the oxidabilities which can be observed even in p‐cymene (in comparison with cumene).
Azomethinfarbstoffe ‐ Sensibilisatoren, Löscher und Reaktionspartner für Singulettsauerstoff
Authors: Grossmann N. , Winnig B. , Weise A. , Fanghänel E.
Published: December 2004

Azomethine Dyes — Sensitizers, Quenchers and Reaction Partner for Singlet Oxygen

Azomethine dyes show photofading in photographic materials, possibly due to oxidation by singlet oxygen. The azomethine dyes 1a–h, 2a–h, 3c, d, f are inefficient photosensitizers of singlet oxygen formation. In tetrachloromethane the quantum yield ϕ1O2 is in the range between 8 · 10−4 and 4 · 10−3.

Contrary to the literature we found that azomethine dyes react with 1O2 (kr). The reaction constants were measured by a competetive technique using 9, 10‐diphenyl anthracene and methylene blue as 1O2 sensitizer. The values of kr show that the reaction of the dyes with 1O2 can not be ignored. Besides this reaction, 1O2 is also quenched by the dyes (kq). The values of kq point to quenching of 1O2 by the tertiary amino group of the dyes via a CT‐mechanism. This study shows that in photofading of azomethine dyes the oxydation by 1O2 must be taken into consideration.
The influence of cation complexation in NaClO3 and KClO3 by crown ethers on the electronic structure of salts studied by 35Cl‐N.Q.R. method
Authors: Nogaj B. , Schroeder G. , Maćkowiak M.
Published: December 2004

Me⊕ (Me = Na; K) cations in MeClO3 chlorates were complexed by crown ethers (CE): 12C4, 15C5 and 18C6 in solution. In the solid phase we could obtain only Na(15C5)ClO3 and K(18C6)ClO3 complexes significant shift in 35Cl‐n.q.r. frequency with respect to the frequency of pure sodium and potassium chlorates was observed. The shifts at 77K were –2.879 MHz for Na(15C5)ClO3 and –1.004 for K (18C6)ClO3.

For other reaction mixtures the 35Cl‐n.q.r. frequencies observed were the same as for the appropriate pure chlorates which confirmed that the expected complexation in the solid phase had not occurred. The investigation described in this paper proved a rapid increase in selectivity of crown ethers at the transition from the solution to the solid state. Moreover, in the solid phase of Me(CE)ClO3 complexes a significant increase was found in the shielding effect of the Me⊕ cation by the surrounding crown ether.
On the Estimation of the Partial Quantum Yields for phytochrome photoconversion by a nonlinear least‐squares method
Authors: Hermann G. , Mueller Eberhard , Hermann Martin , Ullmann Thomas
Published: December 2004

A nonlinear least‐squares method is presented which enables the estimation of the partial quantum yields of a photoreversible two component system by fitting the corresponding kinetic equation directly to experimentally measured data.

The principles of this method are discussed with reference to the photochromic transformation of phytochrome as an adequate model. It is demonstrated that this method yields sufficiently accurate and highly reliable results.

In addition, the advantage of the nonlinear least‐squares method when compared with the so‐called formal integration method and with the initial rate approach is emphasized.
Über die Katalyse der PRILEŽAEV‐Reaktion
Authors: Schnurpfeil D.
Published: December 2004

About the Catalysis of the PRILEŽAEV Reaction

It is shown that a catalysis of the PRILEŽAEV reaction exists. We investigated the influence of homogeneous molybdenum catalysts on the epoxidation reaction of olefins with percarboxylic acids kinetically. The second order reaction rate data show that the MoO2(acac)2 catalyzed cyclohexene epoxidation with peracetic acid runs two times faster than the uncatalyzed reaction and the same epoxidation of oct‐1‐ene runs 15 to 30 times faster. In the same way the reduction of activation parameters in the catalytic reaction proves the catalytic effect. An influence of catalyst concentration and a formation period at the beginning of the catalytic reaction were observed. The influence of the structure of olefin and of the kind of catalyst were investigated and discussed. A formulation of the transition state is given and discussed in relation to the uncatalyzed PRILEŽAEV reaction and to the Halcon reaction.
Zur Anwendung der NMR‐Verschiebungsreagenztechnik bei Substanzen mit zwei unterschiedlichen Assoziationszentren
Authors: Radeglia R. , Zepter R. , Wentzke M.
Published: December 2004

On the Application of the N.M.R. Shift Reagent Technique to Substances with Two Different Association Sites

The competition of two potential association sites of the same substrate molecule for the shift reagent is described by a simple association model. The relative equilibrium constants are determined by the dependence of the induced shifts observed on the amount of the added shift reagent. An example of 3.17‐bifunctionalized steroids demonstrates the applicability of the method.
Dreikomponentenreaktionen. XVII. Endständig reaktive Oligooxyethylenstrukturen aus Alkenen, Chlor und O‐Nucleophilen und deren Umsetzung zu Oxathiaalkanen
Authors: Beger J. , Pöschmann C. , Shabanov A. L. , Gurbanov P. A.
Published: December 2004

Three Component Reactions. XVII. Terminal Reactive Oligooxyethylene Structures from Alkenes, Chlorine and O‐Nucleophiles and Their Transformation into Oxathiaalkanes

The reaction of alkenes, chlorine and oxirane, dioxane, ethyleneglycole, oligoethylenglycoles, the monoethers of oligoethyleneglycoles, ethylene chlorohydrine or α‐hydro‐ω‐chloro‐oligooxyethylenes leads to compounds 6‐‐9, which contain mono or oligoether functions and one or two reactive terminal chlorine atoms. Oxathiaalkanes (10 and 12) were obtained in the reaction of such compounds with sodium mercaptides.
Untersuchungen zur Tautomerie von o,o'‐Dihydroxy‐azofarbstoffen der Eriochrom‐Reihe
Authors: Sagaster Hans‐Rainer , Röbisch Gerhard , Mehlhorn Achim
Published: December 2004

Investigations on the Tautomerism of o,o'‐Dihydroxy Azo Dyes of the Eriochrome Type

Investigation of the u.v.‐vis‐, 1H‐ and 13C‐n.m.r. spectra of the title substances and the isomers 3 and 3p at different pH‐values and in different solvent mixtures as well as of O,O'‐dimethyl derivatives of 2 and 3 show that in aqueous solution as well the monoanions as the trianions exist in the azo forms only. The dianions exist in dependence on the solvents as mixtures of tautomers. The results of PPP calculations for different prototropic structures are in good accordance with the experimental results.
Molecular Complexes of Cyclophanes. XIV. Charge‐transfer complexes of polynuclear[2.2] paracyclophanes with π‐acceptors
Authors: Mourad Aboul‐Fetouh E. , Akkermann‐Kubillus Anja , Hucker Joachim
Published: December 2004

The charge‐transfer (CT) spectra of the π‐complexes formed by several π‐acceptors with some polynuclear[2.2]paracyclophanes have been measured. Comparison of these CT complexes with those of model compounds supports the existence of the transannular electronic interactions in the paracyclophane nucleus. The infrared spectra of a number of CT complexes reveal the increase of the electron density on the π‐acceptor molecule in the CT complexes. Some crystalline CT complexes were prepared and analysed.
Protonierung und Solvatation schwacher organischer Basen. IV. H‐NMR‐spektroskopische Bestimmung der Basizität aliphatischer Ketone
Authors: Roth H. , Freiberg W. , Kröger C.‐F.
Published: December 2004

Protonation and Solvation of Weak Organic Bases. IV. 1H‐N.M.R. Spectroscopic Determination of the Basicity of Aliphatic Ketones

From protonation ratios for a series of methyl and ethyl alkyl ketones 1—13 with gradually branched alkyl groups in the H2O–H2SO4 system, determined by 1H‐n.m.r. spectroscopy, basicity and solvation parameters are systematically estimated by application of extrapolation procedures based on the Hammett acidity function H0 or the excess acidity X.
Revisitation of Formaldehyde Aniline Condensation. VIII. Monomeric N‐methylene anilines
Authors: Giumanini Angelo G. , Verardo Giancarlo , Poiana Marco
Published: December 2004

A convenient, high yield “dry” method of synthesis of monomeric N‐methyleneanilines (6a—i) and the characterization of the products by m.s., 1H‐ and 13C‐n.m.r. and i.r. are reported, improving previous procedures and describing new compounds. It appeared that the existence of monomeric N‐methyleneanilines is strictly related to the presence of enough steric hindrance to oligomerization by substituents in ortho positions. Moreover, some addition products of formaldehyde to an amine and its corresponding imines are tentatively identified on the basis of the observed mass spectrum of the whole reaction mixture.

The reaction products of formaldehyde with 2,6‐dimethylaniline (1a) provided an example of a mobile equilibrium between monomeric and trimeric imine.
Reaktionen unter Beteiligung von Ylid‐Zwischenstufen. III. Zur Darstellung und Konfigurationsanalyse spirokondensierter Tetrahydroindolizine
Authors: Thurner J.‐U. , Richter W. , Köppel H. , Tomaschewski G. , Hauser A. , Van Binst G.
Published: December 2004

Reactions by Participating of Ylide‐Intermediates. III. On Preparation and Structural Elucidation of Spiro‐condensed Tetrahydroindolizines

N‐(Fluroen‐9‐yl)‐pyridinium‐ and ‐isoquinolinium ylides (5) to (8) react with electrondeficit olefinic dipolarophiles under mild conditiones to give satisfactory to good yields of the corresponding spirocondensated tetrahydroindolizines (10) to (13). The structure and configuration of all isolated products were elucidated by spectroscopical methods, especially by 1 D‐ and 2 D 1H‐n.m.r. The 1.3‐dipolar cycloaddition produced regiospecific cycloadducts. From the observed regiospecifity of unsymmetrically substituted olefines (9) can be concluded that the cycloaddition is HOMO(1.3‐dipole) — LUMO(dipolarophile) controlled. The olefines (9) add stereospecifically under retention of their configuration via exo as well as endo transition states. The nitrosubstituted ylides (6) and (8) produced always mixtures of diastereomeric cycloadducts (11) and (13).
Cyclofunktionalisierung von 2‐Allyl‐phenolen mit Schwefelchloriden. 2‐Arylthiomethyl‐2,3‐dihydrobenzofurane aus 2‐Allyl‐ und 2‐Methallyl‐phenolen und Arylsulfenylchloriden
Authors: Mühlstädt M. , Meinhold H. , Muslih R. M.
Published: December 2004

Cyclofunctionalization of 2‐Allyl‐phenols with Sulfur Chlorides: Synthesis of 2‐Arylthiomethyl‐2,3‐dihydrobenzofurans by Reaction of 2‐Allyl‐ and 2‐Methallyl‐phenols, Respectively, and Arylsulfenyl Chlorides

Reactions of acetylamino substituted 2‐allyl‐phenols (1 and 2), and 2‐methallyl‐phenol (6), respectively, with different arylsulfenyl chlorides (3a—d) yield the products of a cyclofunctionalization 5‐ or 7‐acetylamino‐2‐arylthiomethyl‐2,3‐dihydrobenzofurans (4a–d) or (5a–d) and 7‐acetylamino‐2‐arylthiomethyl‐2‐methyl‐2,3‐dihydrobenzofurans (7a–d). The compounds 7 are the first examples of cyclofunctionalization of 2‐methallylphenols by means of sulfur chlorides. The identification of the products was carried out by mass spectrometry, 1H‐n.m.r. spectroscopy and elemental analysis.
Zur Reaktion von N‐(N′,N′‐Dialkyl(aryl)amino‐thiocarbonyl)benzimidoylchloriden mit Kaliumthiocyanat
Authors: Weber G. , Hartung J. , Beyer L.
Published: December 2004

Reactions of N‐(N′,N′‐Dialkyl(aryl)amino‐thiocarbonyl)benzimidoylchlorides with Potassium Thiocyanate

The treatment of the title compound N‐(amino‐thiocarbonyl)‐benzimidoylchloride 1 with potassium thiocyanate leads in dependence on the solvents (methanol, acetic acid, acetone) either to the 1,3,5‐thiadiazine‐2‐thione 2a–d or to the ring opened isothiocyanate 4a, b. In the case of methanol the N‐(amino‐thiocarbonyl)benzimidates were formed as by‐products.

The structure of the products is confirmed by analytical data and by chemical transformations. 2a reacts with methyl iodide to form the 2‐methylthio‐6‐morpholino‐4‐phenyl‐1,3,5‐thiadiaziniumiodide 3a. From 4a and water the N‐(morpholino‐thiocarbonyl)benzamide 5a arises. The reaction of morpholine with 4a yields the benzamidine 6a.
Polycarbonyl heterocycles. VI. A 13C‐N.M.R. study on the structure of H‐bonded ion pair: 3‐Benzoyl‐pyrrolidine Derivatives/Piperidine
Authors: Zaleska Barbara
Published: December 2004

Comparison of spectral data obtained from 13C n.m.r. analyses for compound 1–6 implies the structure of H‐bonded ion pairs 2, 4, 6. In the formation of ion pair 2 the exo‐enol tautomeric form “b” is involved, on the other hand, the endoenolic form “c” is a main tautomer producing the H‐bonded ion pair 4. A stereospecific transformation of compound 5 leads to formation of complex 6 with aliphatic amine.
Änderung der Lichtabsorption von 4′‐Diethylamino‐α‐cyanostilben‐4‐diazoniumionen durch Komplexbildung mit Ethylenglycolderivaten, Kronenethern und Valinomycin
Authors: Walkow F.
Published: December 2004

Colour Change of 4‐Diethylamino‐α‐cyano‐stilbene‐4‐diazonium Ions by Complex Formation with Ethylenglycol Derivatives, Crownethers and Valinomycine

The formation and light absorption of complexes consisting of coloured stilbene‐4‐diazonium ions and different ethylenglycoles, crownethers and valinomycine were investigated. On complex formation the longest wavelength absorption band of the diazonium compounds shifts hypsochromically. This hypsochromism is solvent dependent. The difference between the absorption maximum of a free and complexed diazonium ion increases with increasing polarity and decreasing n‐donicity of the solvents. Other complex forming cations are able to replace the diazonium ions in the complexes, whereby the colours of the original diazonium ions are regenerated. These colour changes can be used to indicate the ability of n‐donor compounds to act as an ionophore.
An improved synthesis of (24R)‐3β‐(2H‐Tetrahydropyran‐2‐yloxy)cholesta‐5,7‐diene‐24,25‐diol – a key intermediate in the synthesis of (24R)‐24,25‐dihydroxyvitamin D3
Authors: Schrötter E. , Landmann Elfi , Schick H. , Schönecker B. , Hauschild U. , Droescher P.
Published: December 2004

A multistep procedure for the conversion of ergosterol into the tetrahydropyranyl ether of (24R)‐24,25‐dihydroxyprovitamin D3 using 1,4‐dihydrophthalazine‐1,4‐dione as diene protecting agent was compared with an established route, which uses 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione for the protection of the diene system. The disclosed reaction sequence allows to double the overall yield. The 1,4‐dioxo‐1,2,3,4‐tetrahydrophthalazin‐2,3‐ylene group proved to be the better diene protecting group in the ozonolytic degradation of the ergosterol side chain. Maintaining the protecting group in the next reaction steps offered further advantages by diminishing the air and light sensitivity of the intermediates.
On the correlation of binary Liquid‐Liquid Equilibria of dipolar aprotic solvents with saturated hydrocarbons
Authors: Kietz E. , Bittrich H.‐J.
Published: December 2004

The results of the correlation of binary liquid‐liquid equilibria data in the title systems demonstrate the importance of the correct description of the critical region with the applied model equations.

Using the Cox‐Herington model and equations characterizing common features in the thermodynamic behaviour in these mixtures general rules for solubility and critical mixing data were derived and tested.
Synthesis and X‐ray structure analysis of 2‐[cyano(aryl)‐methylene]‐imidazolidines, ‐hexahydropyrimidines, and ‐hexahydro‐1H‐1,3‐diazepines
Authors: Huang Zhi‐Tang , Gan Wei‐Xing , Wang Xiao‐Jun
Published: December 2004

2‐[Cyano(aryl)methylene]‐imidazolidines (7), ‐hexahydropyrimidines (8) and ‐hexahydro‐1H‐1,3‐diazepines (9) were synthesized by the reaction of (dimethylthiomethylene)‐phenylacetonitriles (6) with ethylenediamine, 1,3‐diaminopropane and 1,4‐diaminobutane, respectively. These molecules were designed to study the tautomeric equilibrium between the ketene aminal form and the amidine form by changing the substituent on the para position of the phenyl group. But all the products obtained were the ketene aminals. Because the phenyl group was twisted over 30° from the plane containing the two nitrogen atoms and the double bond as shown by the crystal structure of 7a, 8a and 9a, the substituents had no effect on the equilibrium.
Secosteroids. I. Synthesis of vic‐Diols in B‐Secocholestane Group
Authors: Rodewald W. J. , Piotrowski G. T.
Published: December 2004

The transformation of 3‐β‐methoxycholest‐5‐en‐7‐on 1 into B‐secodiols 10, 11 and 12 is described. Reduction of lactone 2, obtained from 1, yielded diol 5 which was acetylated to monoacetate 6. The latter, after dehydration to a mixture of olefins and its hydroxylation, afforded the final products 10, 11 and 12. It has been established that in the reaction of monoacetate 6 with phosphorous oxychloride in pyridine in addition to the β‐elimination, migration of a double bond and Wagner‐Meerwein rearrangement occur.
Der „Normalisierungsfaktor”︁ für die Tomatenmutante Chloronerva. XXXIII. Synthese von Glycinanaloga des Nicotianamins
Authors: Faust J. , Schreiber K.
Published: December 2004

The Normalizing Factor for the Tomato Mutant chloronerva. XXXIII. Synthesis of Glycine Analogues of Nicotianamine

The sarcosine analogue 16 and the glycine analogue 17 of nicotianamine (1) were synthesized by stepwise combination of the sarcosine and glycine esters, respectively, and the protected (S)‐aspartic‐β‐semialdehyde 4 by reductive alkylation. Whereas the sarcosine analogue 16 showes nearly the same biological activity as nicotianamine, the glycine analogue 17 only exhibits a weak biological effect with regard to the phenotypical normalization of the tomato mutant chloronerva.
Photochemie von Bis‐2H‐tetrazolen. V. Kurzzeitspektroskopischer Nachweis von Bisnitriliminen
Authors: Weinberg P. , Grummt U. W. , Csongar Ch.
Published: December 2004

Photochemistry of Bis‐2H‐tetrazoles. V. Flash Spectroscopic Indication of Bisnitrile Imines

The flash photolysis of bis‐2H‐tetrazoles 3‐‐hyphen;6 was investigated. Nitrile imines were detected spectroscopically as short living intermediates. The absorption maxima of the bis(nitrile imines) 9‐‐hyphen;12 are between 360 and 450 nm. The values are in agreement with those obtained by low temperature photolysis of bis‐2H‐tetrazoles. For some bis(nitrile imines) a strong influence of the temperature on the absorption maxima was found. The reaction kinetics of bis(nitrile imines) in ethanol and cyclohexane in the presence of acetic acid and acrylonitrile are described.
Kinetische Untersuchungen zum Alkylierungsvermögen von Dithiophosphorsäureestern im binären Solvensgemisch Methanol/Wasser [1, 2]
Authors: Füllbier B. , Schultze K. , Haberland D.
Published: December 2004

Kinetic Investigations on the Alkylation Capacity of Dithiophosphoric Acid Triesters in Binary Solvent Mixtures Methanol/Water

The influence of solvent polarity on the alkylation capacity of dithiophosphoric acid triesters towards the nucleophiles trimethylamine and monomethylamine is investigated. Different binary mixtures of methanol and water and also the pure compounds are used as solvents. The observed effects are described quantitatively on the basis of Linear Free Energy Relationships by means of empirical parameters of the solvent polarity. Good results are obtained by correlation of the rate constants with the concentration of the polar component cp by Langhals.
Studies on the Decomposition of Alkyl Hydroperoxides by different catalysts
Authors: Lauterbach Gerlinde , Pritzkow W. , Tien Tieu Dung , Voerckel V.
Published: December 2004

The catalytic decomposition of cumene, 1‐methylcyclohexyl and cyclohexyl hydroperoxides was studied in cyclohexane, cis‐ and trans‐1,4‐dimethylcyclohexane and cis‐pinane as the solvents. The stearates and the acetylacetonates of manganese, cobalt and chromium, the acetylacetonates of molybdenum and vanadium, n‐butyl orthoborate and n‐butyl metaborate were used as the catalysts. The chromium‐, vanadium‐, molybdenum‐ and boron‐containing catalysts brought about some Hock‐type decomposition of cumene hydroperoxide and thus proved to be acidic. Of these more of less acidic catalysts only molybdenyl acetylacetonate effected a partially stereospecific hydroxylation of the tertiary CH‐bonds in cis‐ and trans‐1,4‐dimethylcyclohexane. The well‐known selectivity of chromium catalysts for the ketone formation during the decomposition of secondary hydroperoxides is caused by the catalytic oxidatio of secondary alcohols by hydroperoxides in the presence of chromium compounds.

In the presence of all the catalysts used the free‐radical pathways of the hydroperoxide decomposition predominated, and the attack of the intermediate radicals on the starting hydroperoxide was more important than the attack on the solvent molecules.
Amphiphile Aggregation in konzentrierten Säuren Grenzflächenaktivität von N‐(n‐Alkyl)‐pyridinium‐Salzen in Schwefelsäure
Authors: Müller Annerose , Miethchen R.
Published: December 2004

Amphiphilic Aggregation in Concentrated Acids. Interfacial Activity from N‐(n‐Alkyl)‐Pyridinium Salts in Sulfuric Acid

The critical micelle concentration of N‐(n‐alkyl)‐pyridinium salts in sulfuric acid of different concentrations was determined by measurements of their surface tension and interfacial tension changes. The concentration of surface saturation Γmax and surface area per molecule F were calculated from the slope of decreasing parts of surface tension lines VS log c. The influence of counter ion and anorganic additives was studied.
Synthesis of pyrroles, a diazepindione and substituted 3‐aminoacrylonitriles by reaction of Bisalkylthioacrylonitriles with α‐aminoacid derivatives
Authors: Erdmann Barbara , Knoll A. , Liebscher J.
Published: December 2004

3,3‐Bisalkylthioacrylonitriles (2), substituted by a cyano, carboxylate or amido group at position 2 react with derivatives 5 of α‐aminoacids by monosubstitution under the formation of 3‐carbonylmethylaminoacrylnitriles (6) or by substitution and cyclisation to 5‐alkylthio‐3‐aminopyrrole‐2‐carboxylates (7) or the tetrahydro‐1,4‐diazepin‐2,7‐dione (8).
On the Acetylation of Phenanthrene and 9‐chlorophenanthrene
Authors: Fernández Franco , Gómez Generosa , López Carmen , Santos Ana
Published: December 2004

Friedel‐Crafts acetylation of phenanthrene (1a) in sym‐tetrachloroethane yields mixtures of 2‐, 3‐ and 9‐acetylphenanthrenes (2a, 3a, 4). The distribution of isomers is found to depend strongly upon the method of mixing the reagents. Acetylation of 9‐chlorophenanthrene (1b), performed by a variety of methods and solvents, led mainly to 3‐acetyl‐9‐chlorophenanthrene (3b) (≥85%). Previously unreported 2‐acetyl‐9‐chlorophenanthrene (2b) was found to form up to a maximum 11% in nitrobenzene.
Chalkonaziridine. IV. Vergleich des spektroskopischen und massenspektrometrischen Verhaltens von trans‐Chalkonaziridinen und trans‐Chalkonepoxiden
Authors: Weber F. G. , Liepert H. , Radeglia R. , Köppel H.
Published: December 2004

Chalcone Aziridines. IV. Comparison of Spectroscopical and Mass Spectrometrical Behavior of trans‐Chalcone Aziridines and trans‐Chalcone Epoxides

The aziridines 1 were compared with epoxides 2 by their i.r. and n.m.r. spectroscopical behavior and the threemembered ring electron densities. In the masse spectra we found not only identical path‐ways i. e. the formation of M⊕ and Ar2CH⊕ ions and onium or aryl fragmentation, but also differences as the formation of [M–17]⊕ ions for 1 and carbonyl rearrangements for 2.
Chinoxaline. XXVI. Synthese von bis‐azolo[a,c]kondensierten Chinoxalinen. I. Darstellung aus 4‐substituierten 1,2,3‐Triazolo[1,5‐a]chinoxalinen
Authors: Vogel M. , Lippmann E.
Published: December 2004

Quinoxalines. XXVI. Synthesis of Bis‐azolo[a,c]‐fused Quinoxalines. I. Synthesis from 4‐Substituted 1,2,3‐Triazolo[1,5‐a]quinoxalines

The synthesis of bis‐azolo‐fused quinoxalines of type. 6 is described. The new bisazolo‐fused compounds 9, 10a, b, 12, and 16 were synthesized from the 4‐substituted 1,2,3‐triazolo‐[1,5‐a]quinoxalines 7, 8, 11, and 13 by intramolecular cyclization reactions. The structures were determined by microanalysis, i.r., 1H‐n.m.r., and mass spectra.
Regio‐ and stereoselectivity of 1‐(Pyridazin‐3‐yl)‐3‐oxidopyridinium Betaines towards 2π‐ and 4π‐conjugated olefins
Authors: El‐Abbady S. A. , Ahmed M. G. M. , Abdulhamid H. A. , Shalaby A. A. , Moustafa A. H.
Published: December 2004

1‐(6‐Phenyl) and 1‐(6‐(4‐tolyl)‐3‐oxidopyridinium betaines (1a, b) react as 1,3‐dipoles with conjugated olefines, namely 4‐vinylpyridine, ethyl cinnamate and styrene as 2π‐1,3‐dipolarophiles to give 2,6‐cycloadducts [6‐substituted‐8‐azabicyclo[3,2,1]oct‐3‐en‐2‐ones (3a, b, 4a, b and 5b)] and with butadiene and furan as 4π‐dipolarophiles to give 2,4‐cycloadducts [7‐substituted‐7‐azabicyclo[4,3,1]deca‐3,8‐diene‐10‐one] and 3‐6‐phenylpyridazin‐3‐yl)‐3‐aza‐10‐oxatricyclo‐[5,2,1,12,6]undeca‐4,8‐diene‐11‐one (9a). Structural and configurational assignments were based on H.n.m.r. spectral analysis.
Vinyloge Acylverbindungen. XXI. 1H‐NMR‐spektroskopische Untersuchungen an 3‐Chlor‐propen‐iminiumsalzen
Authors: Fischer G. W. , Olk B.
Published: December 2004

Vinylogous Acyl Compounds. XXI. 1H‐N.M.R. Spectroscopic Investigations on 3‐Chloropropen‐iminium Salts

The 1H‐n.m.r. data of a series of 3‐aryl‐3‐chloropropeniminium salts 5 are reported. From the vicinal coupling constants 3J(H1, 2H) as well as from NOE difference spectra follows that salts of type 5 have throughout E(1,2)Z(2,3) configuration.
Photochemie von Acylaziden. III. Direkte und sensibilisierte Photolyse von p‐Trimethylsilylbenzoylazid in fluider Phase und in polymeren Schichten
Authors: Abraham W. , Siegert St. , Kreysig D.
Published: December 2004

Photochemistry of Acylazides. III. Direct and Sensitized Photolysis of p‐Trimethylsilylbenzoylazide in the Fluid Phase and in Polymeric Layers

The photochemistry of the title compound in cyclohexane was investigated by direct and sensitized excitation, respectively. The only products which could be detected by means of HPLC were the rearrangement product isocyanate from the singlet azide and the insertion product into the solvent via the singlet nitrene, respectively. Products via the triplet states were not formed by direct photolysis. The generally high quantum yields of the photolysis of the acylazide 1 are strongly dependent on the concentration. At 0.1 M the quantum yield amounts to 4.

The photolysis was sensitized by several triplet generators creating the abstraction products as main products. But also insertion products were formed via the triplet azide. From the results a triplet ground state of the nitrene is postulated. The sensitization can be realized also by electron donors like diphenylanthracene, pyrene or perylene. An electron transfer to 1 is assumed. The products of this sensitization are the same as via the direct photolysis.

The results in solutions can be applied to polymers. The modification of polymers (silylation by the nitrene formed) is possible in this way.
Nitriles in Organic Synthesis: Synthesis of new pyridazine, pyridine and pyrazolo[3,4‐b]pyridine derivatives
Authors: Ibrahim Nadia Sobhy , Mohamed Mona Hassan , Mahfouz Youssef , Elnagdi Mohamed Hilmy
Published: December 2004

The reaction of diethyl monoiminomalonate with benzoylacetonitrile affords the ethyl 3‐amino‐4‐cyanopentanoate derivative 1 a. Compound 1 a condensed with salicylaldehyde to yield the coumarin 5 and coupled with arenediazonium salts to yield the arenehydrazones 6a–c. Compounds 6a, b could be converted into the aminopyridazinium carboxylate 8a, b on treatment with aqueous sodium hydroxide. The reaction of 6a–c with hydrazine and phenyl hydrazine is reported.
Reactions of Alcohols with 0,0‐Diethylphosphorothioic and 0,0‐diethylphosphorodithioic acid in the presence of triphenylphosphine and diethyl azodicarboxylate II. 31P‐N.M.R. Studies
Authors: Młotkowska B.
Published: December 2004

Low temperature 31P‐n.m.r. studies of the reaction of 0,0‐diethylphosphorothioic acid with triphenylphosphine and diethyl azodicarboxylate revealed that, at low temperatures, the only intermediate is the protonated betaine, even in the presence of neopentyl alcohol. Above 0°C this species reacts with neopentyl alcohol to produce the neopentoxytriphenylphosphonium salt which decomposes to isomeric diethyl neopentyl phosphorothioates and triphenylphosphine oxide, at elevated temperatures. The reaction of ethanol with 0,0‐diethylphosphorodithioic acid leads mainly to 0,0,S‐triethyl phosphorodithioate and triphenylphosphine oxide. In addition, a small amount of 0,0,0‐triethyl phosphorothionate and triphenylphosphine sulfide were detected. The mechanism of these reactions is suggested.
Synthese von 5‐Hetaryl‐1,3‐dithiol‐Derivaten durch Reaktion von Hetarylmethyl‐dithiokohlensäurediestern mit Schwefelkohlenstoff
Authors: Dölling W. , Hildebrandt Andrea
Published: December 2004

Synthesis of 5‐Hetaryl‐1,3‐dithiole Derivatives by Reaction of Hetarylmethyl‐dithiocarbonates with Carbon Disulfide

(Pyrid‐2‐yl)‐ and (quinol‐2‐yl)‐dithiocarbonates 4 and 7 cyclocondense with carbon disulfide to yield 4,5‐disubstituted 1,3‐dithiole‐2‐thiones 5 and 8a–d after alkylation reaction. 8 is transformed into the 2‐oxo‐derivatives 9 by reaction with mercuric acetate. A series of heterocyclic substituted dithiocarbonates 10a, 10b, 12a, 12b, and dithiocarbamates 12c–g, respectively, is synthesized by reactions of halomethylheterocycles with the corresponding salts of xanthates or dithiocarbamates.
Untersuchungen zur Photolyse von Diaryliodoniumsalzen
Authors: Timpe H.‐J. , Schikowsky V.
Published: December 2004

Investigations on Photolysis of Diaryliodonium Salts

The photolysis of diaryliodonium salts in solution leads to various competitive and consecutive reactions. Upon irradiation, the excited state desactivates mainly through homolytic cleavage of the CI‐bond, but to a minor extent also through heterolytic cleavage of the same bond. Thus, several photolysis products have been obtained: aromatics, new iodonium salts, iodoaromatics, substitution products of the solvent, protonic acid in aqueous solutions, iodide and iodate ions and iodine. In the case of diphenyliodonium iodide the yields of iodine are higher compared to those of other salts because of electron transfer processes. The quantum yields of the disappearance of the iodonium salt (ΦI) and of the formation of protonic acids (ΦP) are equal within the experimental error. These values do not depend on the nature of the solvent, with the exception of H‐donor solvents, on the initial salt concentration and on oxygen. But, they depend strongly on the light intensity and on the substituent at the aromatic ring. The ΦP‐data also depend on the oxidation potential of the anion used. For diphenyliodonium chloride, the quantum yield of iodobenzene formation reaches only the half of the values for ΦI and ΦP. A kinetic scheme is given for the explanation of the light intensity dependence, which is based on 1. and 2. order reactions of intermediates formed by the homolytic pathway. It is assumed, that the electron transfer reaction by iodide salts proceeds only between the iodide ion and the intermediate products.
Heterocyclic synthesis with nitriles: Syntheses of some novel pyrazolo[1,5‐a]pyrimidine and Pyrrolo[2′,3′:3,4]pyrazolo[1,5‐a]pyrimidine Derivatives
Authors: Abdelrazek F. M.
Published: December 2004

3,5‐Diamino‐4‐phenacylpyrazoles 1a, b react with the cinnamonitriles 2a, b to afford the novel 7‐phenacylpyrazolo[1,5‐a]pyrimidine derivatives 4a–d, respectively. Compounds 4c, d undergo cyclization with trichloroacetonitrile to afford the novel tricyclic system pyrrolo‐[2′,3′:3,4]pyrazolo[1,5‐a]pyrimidine derivatives 5e, f, respectively.
Synthesis, spectral data and extraction of copper by 1‐(2′‐Hydroxy‐5′‐alkylphenyl)‐1‐alkanone Oximes
Authors: Krzyżanowska Ewa , Olszanowski A. , Juskowiak M.
Published: December 2004

1‐(2′‐Hydroxy‐5′‐alkylphenyl)‐1‐ethanone oximes with a normal alkyl group containing 2 to 12 carbon atoms and 1‐(2′‐hydroxy‐5′‐methylphenyl)‐1‐alkanone oximes containing 1 to 11 carbon atoms in the hydrocarbon chain were synthesized. Spectral data (u.v., i.r., n.m.r. and 13C) of oximes are reported. Four of these oximes were used for copper extraction from acidic solution. The results obtained indicate, that these oximes are better extractants than alkyl derivatives of 2‐hydroxybenzophenone oximes.
Thermal Decomposition of Phenyl Alkyl Ethers
Authors: Ondruschka B. , Engelstädter U. , Vorwerk D. , Zimmermann G.
Published: December 2004

Reaction products and intermediates of the thermal conversions (temperature range: 600 to 1200°C, total pressure about 120 mPa) of phenyl methyl ether (1), phenyl ethyl ether (2), and m‐cresyl methyl ether (3) were determined in a pyrolysis apparatur set combined with mass spectral „real time”︁ analysis. In all cases, the predominant initial process was PhO–R bond homolysis. Phenoxy type radicals thus generated decompose unimolecularly to cyclopentadienyl type radicals and carbon monoxide. In runs with 1 and 2 cyclopentadienyl dimers (C10H10) were formed and, in addition, at temperatures >1000°C, naphthalene (C10H8). Under similar conditions the m‐methylphenoxy radical (from 3) suffers CO elimination providing the methylcyclopentadienyl radical which chiefly gives benzene instead of the dimers or the products derived from it. Under the applied conditions only bimolecular stabilization of the unsubstituted cyclopentadienyl radical proved possible, whereas the methyl substituted radical has a chance for unimolecular stabilization, too, as a result of which fulvene is formed through the loss of hydrogen. Fulvene is a direct benzene precursor.
The Autoxidation of Hept‐3‐yne
Authors: Brose Th. , Pritzkow W. , Sebald F. , Voerckel V.
Published: December 2004

In the reaction mixtures of the oxidation of hept‐3‐yne with molecular oxygen as products of the attack on the CC triple bond heptane‐3,4‐dione, propionic and butyric acids and a very small amount of 2‐ethylvaleric acid were found. Hept‐2‐en‐4‐one and hept‐3‐en‐5‐one were probably present, but could not be identified unambiguously. As in the case of the isomeric octynes the main primary reaction products were the hydroperoxides formed by attack on the CH bonds in α‐position to the CC triple bond.
Spektroskopische Untersuchungen an 4‐Nitrophenylhydrazonen sekundärer und tertiärer α‐Ketocarbonsäureamide
Authors: Waldheim G. , Möhrle H. , Rüdiger S.
Published: December 2004

Spectroscopic Studies on 4‐Nitrophenylhydrazones of Secondary and Tertiary α‐Ketoamides

4‐Nitrophenylhydrazones of secondary and tertiary α‐ketoamides both exist in two stable isomeric forms (E/Z) with respect to the position of the substituents at the CN‐Bond. But whereas the Z‐form of the secondary amides can be easily assigned by means of intramolecular hydrogen bond, this criterion in case of most the derivatives of tertiary amides fails. As shown by derivatives of glyoxylic acid this deviation is evidently caused by steric facts due to the double substituted amide group and the alkyl residue on the α‐C‐atom.
Zur Umsetzung von Oxalamidinen mit Heterocumulenen der Kohlensäurereihe zu Imidazolidin‐Derivaten
Authors: Beckert R. , Gruner M.
Published: December 2004

On the Reaction of Oxalic Amidines with Carbonic Acid Derived Heterocumulenes to Imidazolidine‐Derivatives

A useful synthetic route to nonsymmetric derivatives of imidazolidine (derivatives of parabanic acid) is demonstrated by the reaction of tetraarylated oxalic amidines 1 with different alkyl‐ and aryl substituted isothiocyanates 4, isoselenocyanates 31, and carbodiimides 30.

Acylisothiocyanates 9 react differently leading to a mixture of three cycloacylation products 12, 13 and 14. Silylated heterocumulenes such as 25 and 26 react with 1 to give 28 and 29 transsilylation. Based on the 13C‐n.m.r. spectroscopic investigation of the reaction between 1a and methyl isothiocyanate and phenyl isothiocyanate respectively a mechanism is proposed.
Spectral Sensitization of Dediazoniation by the 2‐electron‐transfer system meso‐tetraphenylporphinato‐dichlorostannate(IV)/10‐methyl‐9‐Phenyl‐9.10‐dihydro‐acridine
Authors: Becker H. G. O. , Grossmann Katrin
Published: December 2004

The photoreduction of meso‐tetraphenylporphinatodichlorostannate(IV) (SnCl2TPP) by 9‐phenyl‐10‐methyl‐9,10‐dihydro‐acridine (ACH) in 1,2‐dichloroethane/acetonitrile 1:1 (v/v) under argon proceeds only with a low quantum yield in spite of the fact that ACH is in other cases an excellent 2‐electron donor. The reason may be the formation of a triplet exciplex which opens a new deactivation channel. Evidence for such an exciplex is given by means of the WARE treatment of flash‐photolytic experiments and quantum yields of dediazoniation, Keq ≈ 650 M−1 and τexc = 46 μs.

The exciplex reacts fast with p‐N,N‐dimethylamino‐benzenediazonium tetrafluoroborate (kr = 4.1 × 108 M−1 s−1) under electron transfer leading to dediazoniation. At high ACH concentrations (8 × 10−3 M) the dediazoniation gives even at very low diazonium salt concentrations (≈ 4 × 10−5 M) quantum yields as high as 1.95 (0.37 stemming from sensitization by the SnCl2 complex of tetraphenylchlorine present as an impurity of SnCl2TPP. SnCl2TPP) remains unchanged during the sensitization reaction, i.e. the process is fully photocatalytic.
Méthode d'essai pour apprécier L'aptitude à la déflagration des explosifs
Authors: Bigourd J. , Michot C.
Published: December 2004

La méthode utilisée de fa¸on courante au CERCHAR est la suivante. Les essais sont effectués dans un mortier d'acier qui est fermé hermétiquement par un disque de cuivre résistant à une pression d'environ 300 bar. Dans ce mortier, l'explosif essayé est disposé, sous forme d'une cartouche, à une distance de 15 cm d'une charge de poudre noire qui est mise à feu par allumeur électrique. Suivant l'importance de la charge de poudre, il se produit ou non une déflagration de l'explosif. Celle‐ci est mise en évidence par la rupture du disque de cuivre. D'un essai à l'autre, on fait varier la masse de poudre noire, de fa¸on à obtenir une estimation de la masse qui correspond à une probabilité de 50% de déflagration de l'explosif. Cette méthode s'applique aussi bien aux explosifs classiques qu'aux bouillies explosives et aux mélanges nitrate d'ammonium‐fuel oil.
Nitroureas 1. Synthesis, scale‐up and characterization of K‐6
Authors: Mitchell A. R. , Pagoria P. F. , Coon C. L. , Jessop E. S. , Poco J. F. , Tarver C. M. , Breithaupt R. D. , Moody G. L.
Published: December 2004

The synthesis and characterization of 2‐oxo‐1,3,5‐trinitro‐1,3,5‐triazacyclohexane (K‐6), a cyclic dinitrourea, is described. The laboratory synthesis was scaled‐up to provide 1.6 kilograms of crystalline K‐6 which was used for performance testing. K‐6 was formulated with 5% Viton A and pressed to 96.5% theoretical maximum density (TMD). Performance measurements in the form of front surface velocity measurements (tantalum plate push) and 1‐inch cylinder expansion experiments indicate K‐6 will out‐perform HMX by 4% at early volume expansions. Thermal response and shock sensitivity experiments on K‐6 are also described.
Electrical Performance of Explosive‐Driven Switches for slapper detonator applications
Authors: Podlesak Michael
Published: December 2004

Time dependent resistance measurements were performed on fast, high current electrical switches proposed for use in slapper detonators. The switches, consisting of a copper‐polymer‐copper laminate, are designed to conduct electrically after being impacted by an explosive‐driven copper flyer plate. The polymer film used in our experiments was Kapton (polypyromellitimide) and was expected to exhibit shock induced conduction at pressures of 9 GPa and above. While it is believed that shock pressures in the vicinity of 9 GPa were achieved in the switches, no significant shock conduction effect was observed. This was corroborated by observing identical electrical behaviour for switches based on Teflon (polytetrafluoroethylene) film, which is known to possess good insulating properties even under strong shocks. However, in spite of the lack of evidence of significant shock induced conduction in the Kapton based switch, its operation is satisfactory. The average switch closure resistance at practical voltage and current levels was found to be of the order of 0.15Ω, attained within a closure time of 10 ns to 20 ns. Also, the electrical characteristic of the switch performance was largely independent of the supply voltage, when a low impedance voltage source was used, though the closure resistance values displayed a large scatter with standard deviation of the order of 0.1Ω.
Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCFMOLC(LCGO) Methode. III. Das Cyclopropan (C3H6)
Authors: Preuss H. , Diercksen G.
Published: December 2004

Das C3H6 wurde unter Berücksichtigung aller 24 Elektronen ab initio mit dem Allgemeinen Programmsystem/SCFMOLC(LCGO) Methode berechnet. Es ergab sich nach Variation des CC Abstandes ein Minimum der Gesamtenergie von −116.02 a.E. bei einem CC Abstand von 2.91 a.E. Die Ionisierungsenergie wurde zu 10.33 eV bestimmt.
Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCFMOLC(LCGO) Methode. IV. Das Äthylen (C2H4)
Authors: Diercksen G. , Preuss H.
Published: December 2004

Das C2H4 wird im Gleichgewichtsabstand der Zentren unter Berücksichtigung aller 16 Elektronen ab initio unter Verwendung des Allgemeinen Programmsystem/SCFMOLC(LCGO) Methode berechnet. Es ergibt sich eine Gesamtenergie von −76.77 a.E. Die Ionisierungs‐energie beträgt dabei 10.55 eV.
SCFCI and SCF open‐shell studies of the base components of the nucleic acids
Authors: Kuprievich V. A.
Published: December 2004

The π‐electron structure of adenine, guanine, cytosine, thymine and uracil in their ground, ionized, singlet and triplet excited states are investigated by means of the SCFCI and SCF open‐shell methods. The calculations for singlets fit the maxima of the absorption bands well. The energy difference between the first and the second singlet states of adenine is found to be very small. The open‐shell method leads to the same relative ionization potential as does the SCF (with the integrals empirically corrected). The calculated energies of the triplet states almost coincide in the SCF open‐shell and the SCFCI approximation. The calculated transition energies to the first triplet state of the pyrimidines are higher than in the case of the purines. The value of the singlet–triplet separation energy of purines is in agreement with experimental data.
Simplified SCF calculations for σ‐bonded systems. II. The interhalogens
Authors: Pohl Herbert A. , Raff L. M.
Published: December 2004

A series of simplified LCAOMOSCF calculations has been carried out on the ten possible interhalogen molecules. In the model only the bonding electrons are considered explicitly. The bonded electron pair is described by a single Slater determinant and all integrals are evaluated by unadjusted, semiempirical techniques. Equilibrium separations, binding energies, and potential curves are obtained for each molecule, and the effect of the Wolfsberg–Helmholtz parameter in the off‐diagonal term is studied in detail.

Without empirical adjustment, calculated electronic energies are accurate to about 2% while the bonding energies are too low by about 1 eV. Equilibrium distances are too small. The observed trends of these properties, however, are in satisfactory agreement with experiment. If desired, a single empirical adjustment of the Wolfsberg–Helmholtz parameter, K, suffices to bring the calculated binding energies of the entire series into good agreement with experiment. Previously suggested empirical forms for K yield poor results here and alternate proposals concerning the best procedure for determining, a priori, the best values for this parameter are made.

In general it is concluded that the approximations utilized in this work are compatible and well‐suited for the description of σ‐bonded systems.
Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCFMOLC(LCGO) Methode. IX. Das System (Li2H)−
Authors: Preuss H. , Diercksen G.
Published: December 2004

Das System (Li2H)− wurde für eine Reihe von Kernlagen unter Berücksichtigung aller 8 Elektronen mit dem Allgemeinen Programmsystem/SCFMOLC(LCGO) Verfahren berechnet. Es ergab sich für die lineare symmetrische Anordnung ein stabiles Molekül mit dem Bindungsabstand RLiH = 3,41 a.E. und einer Gesamtenergie von −15,3874 a.E., die um 0,0114 a.E. (0,311 eV, 7,61 kcal/mol) tiefer liegt als die Summe der entsprechenden SCF‐Energien der Systeme LiH und Li−. Die Kraftkonstante der symmetrischen Schwingung ergibt sich zu k = 1,64722 × 106 dyn/cm, aus der die Frequenz zu ω = 1998,9 cm−1 berechnet wurde. Die Ergebnisse werden diskutiert.
Calcul de l'Énergie de Corrélation pour l'État Fondamental de la Molécule d'Acétylène
Authors: Čížek Jíří , Pellégatti Alain
Published: December 2004

Les effects de corrélation dans la molécule d'acétylène sont étudiés à partir d'une méthode utilisant une technique de diagrammes analogues à ceux de Feynman. L'introduction de la réduction des intégrales électroniques atomiques diminue considérablement la valeur de l'énergie de corrélation.
Theoretical considerations of the electronic spectra of methyl flavins
Authors: Song Pill‐Soon
Published: December 2004

Methyl groups in flavins are best treated by the group‐orbital approximation. The pseudo‐heteroatom approximation overestimates methyl hyperconjugation with the Pariser–Parr–Pople SCF–MO method. Singlet π → π* transition energies are calculated by various MO methods with differing degrees of sophistication, and the results from the PPP method agree reasonably with the experimental values. 2‐ and 4‐thioflavin analogs are also treated satisfactorily. The effects of position and number of the methyl groups on the spectra of flavins are described in detail. Rough estimates of the n → π* energies of flavins suggest that the lowest singlet excited state is (π, π*), consistent with the fluorescence and phosphorescence polarization data.