bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of Cyclic ‘ortho’‐Anhydrides of Heptalene‐1,2‐dicarboxylic Acids
Authors: Weber Roland H. , Brügger Paul , Arnold Wolf , Schönholzer Peter , Hansen Hans‐Jürgen
Published: December 2004

1‐(Alkoixycarbonyl)heptalene‐2‐carboxylic acids as well as 2‐(alkoxycarbonyl)heptalene‐1‐carboxylic acids react with the iminium salt formed from N,N‐dimethylformamide (DMF) and oxalyl chloride, in the presence of an alcohol, to yield the corresponding cyclic ‘ortho’ ‐anhydrides (ψ‐esters; cf. Schemes 2,3,6, and 8). When the alkoxy moiety of the acids and the alcohols is different, then diastereoisomeric ‘ortho’ ‐anhydrides are formed due to the non‐planarity of the heptalene skeleton. The approach of the alcohol from the β‐side is strongly favored (cf. Scheme 5 and Table 1). This effect can be attributed to the bent topology of the heptalene skeleton which sterically hinders the approach of the nucleophile from the α‐side of the postulated intermediates, i.e. the charged O‐alkylated anhydrides of type 19 (cf. Scheme 6). Whereas the ‘ortho’‐anhydrides with four substituents in the ‘peri’ ‐positions of the heptalene skeleton are configurationally stable up to 100°, the ‘ortho’ ‐anhydrides with only three ‘peri’ ‐substituents slowly epimerize at 100° (cf. Scheme 7) due to the thermally induced inversion of the configuration of the heptalene skeleton.
Catalytic Intramolecular Palladium‐Ene Reactions. Preliminay Communication
Authors: Oppolzer Wolfgang , Gaudin Jean‐Marc
Published: December 2004

Pd(dba)2[dba = dibenzylideneacetone]/PPh3‐or Pd(PPh3)4‐catalyzed cyclizations of acetoxy‐dienes 2 → 3 and 10 → 11 gave 1‐vinyl‐2‐methylidene‐subsituted cyclopentances and cyclohexanes in high yield, consistent with a palladium‐ene/β‐elimination mechanism (D → E → F, Scheme 2). The efficient and highly stereoselective cyclizations 7 → 7 and 8 → 9 illustrate intramolecular allylpalladium insertions into 1,2‐dialkyl‐, trialkyl‐, trialkyl‐, and cyclic alkenes followed by elimination of the exocyclic β–H giving 1,2‐divinylcyclopentanes. These new olefin insertions proceed faster in AcOH (compared to THF) and occur preferentially cis relative to the Pd (13 → 14 → 15).
Nucleophile Ringöffnung von α‐Nitrocyclopropancarbonsäure‐arylestern mit sterisch geschützter, aber elektronisch wirksamer Carbonyl‐ und Nitro‐Gruppe. Ein neues Prinzip der α‐Aminosäure‐Synthese (2‐Aminobutansäure‐a4‐Synthon)
Authors: Seebach Dieter , Häner Robert , Vettiger Thomas
Published: December 2004

Nucleophilic Ring Opening of Aryl α‐Nitrocyclopropanecarboxylates with Sterically Protected but Electronically Effective Carbonyl and Nitro Group. A New Principle of α‐Amino Acid Synthesis (2‐Aminobutanoic Acid a4‐Synthon)

The readily available 2,4,6‐tri(tert‐butyl)‐and 2,6‐di(tert‐butyl)‐4‐methoxypahenol esters 2 of α‐nitrocyclo‐propanecarboxaylic acid ring opening with C‐, N‐, O‐, and S‐nucleophiles (cyanide, malonate, azide, anilines, alkoxides, phenoxides, thiolates) in DMF or alcohol solvents (80–95% yield). The products 6–14 are 2‐nitrobutanoates with the newly introduced substituent in the 4‐position. Reduction of the NO2 group with Zn/AcOH/Ac2O gives N‐acetyl‐α‐amino acid esters 16–22 (40–90% yield). Subsequent oxidative cleavage (H2O2/HCOOH) of The p‐methoxy‐phenyl esters 18 and 20 produces free amino acids (65% 23 and 67% 24, respectively). Thus, the nitro ester 2 corresponds to a 2‐aminobutanoic‐acid a4‐synthon, it is a ‘homo‐Michael acceptor’ producing γ‐substituted α‐amino acids.
Notiz über die Verwendung von 3‐(Arylsulfonyl)‐2‐cycloalkenonen als 2‐Cycloalkinon‐Synthese‐Equivalente
Authors: Kienzle Frank , Minder Rudolf E.
Published: December 2004

Note on the Use of 3‐(Arylsulfonyl)‐2‐cycloalkenones as Synthesis Equivalents of 2‐Cycloalkynones

3‐(Arylsulfonyl)‐2‐cyclopentenones and 3‐phenylsulfonyl‐2‐cyclohexnone undergo Diels‐Alder reactions with cyclopentadiene. Elimination of arylsulfinic acid leads to products, which would have been obtained directly from a Diels‐Alder reaction of 2‐cyclopentynone or 2‐cyclohexynone.
Cyclodimerization of 1‐(Dimethoxyniethyl)‐5,6‐dimethylidene‐7‐oxa‐bicyclo[2.2.1]hept‐2‐ene Induced by Nonacarbonyldiiron. Crystal Structure of (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)‐ Tricarbonyl[C, 2,3, C‐η‐(1,4‐epoxy‐1,5‐bis(dimethoxymethyl)‐2,3‐dimethylidene‐1,2,3,4,4a,9,9a,10‐octahydroanthracene)]iron
Authors: Bonlantini Edia , Vogel Pierre , Pinkerton Alan A.
Published: December 2004

The transition‐metal‐carbonyl‐induced cyclodimerization of 5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene is strongly affected by substitution at C(1) While 5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept–2‐ene‐l‐methanol (7) refused to undergo [4 + 2]‐cyclodimerization in the presence of [Fe2(CO)9] in MeOH, 1‐(dimethoxymethyl)‐5,6‐di‐methylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene (8) led to the formation of a 1.7:1 mixture of ‘trans’ (19, 21, 22) vs. ‘cis’ (20, 23, 24) products of cyclodimerization together with tricarbonyl[C, 5,6, C‐η‐(l‐(dimethoxymethyl)‐5,6‐di‐methylidenecyclohexa‐1,3‐diene)]iron (25) and tricarbonyl[C,3,4, C‐η‐(methyl 5‐(dimethoxymethyl)‐3,4‐di‐methylidenecyclohexa‐1,5‐diene‐l‐carboxylate)]iron (26). The structures of products 19 and of its exo (21) and endo (22) [Fe(CO)3(1,3‐diene)]complexes) and 20 (and of its exo (23) and endo (24) (Fe(CO)3(1,3‐diene)complexes) were confirmed by X‐ray diffraction studies of crystalline (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)‐tricarbonyl[C, 2,3, C‐η‐(1,4‐epoxy‐1,5‐bis(dimethoxymethyl])‐2,3‐dimethylidene‐1,2,3,4,4a,9,9a,10‐octahydroanthracene)iron (21). In the latter, the Fe(CO)3(1,3‐diene) moiety deviates significantly from the usual local Cs symmetry. Complex 21 corresponds to a ‘frozen equilibrium’ of rotamers with η‐alkyl, η3‐allyl bonding mode due to the acetal unit at the bridgehead centre C(1).
Biologically Active Natural Acetylenic Compounds from Eutypa lata (Pers: F.) TUL
Authors: Renaud Jean‐Marc , Tsoupras Georges , Tabacchi Raffaele
Published: December 2004

Eight new acetylenic compounds have been isolated and identified from the culture medium of the fungus Eutypa lata. Structural elucidation and biological activity are discussed.
Novel Prenylated Xanthones from Garcinia gerrardii HARVEY
Authors: Sordat‐Diserens Isabelle , Marston Andrew , Hamburger Matthias , Hostettmann Kurt , Rogers Colin
Published: December 2004

Three novel prenylated xanthones, 1–3, have been isolated from the root bark of Garcinia gerrardii HARVEY ex T. R. SIM (G. natalensis SCHLECHTER; G. transvaalensis BURTT DAVY; Guttiferae). Structure elucidation was achieved by a combination of one‐ and two‐dimensional NMR spectroscopic techniques, including long‐range HETCOR, mass spectroscopy, and chemical methods. Garcigerrin A (1) and B (2) are pyrano derivatives of 3. They all show a rare 1,4,5 oxygenation pattern of the xanthone nucleus. Xanthone 3 is fungicidal against Cladosporium cucumerinum.
Conversion of Campholene‐ to Necrodane‐Type Monoterpenes. A short stereoselective synthesis of (−)‐(R, R)‐β‐necrodol and its three stereoisomers
Authors: Schulte‐Elte Karl H. , Pamingle Hervé
Published: December 2004

Application of a stereoselective Prins/retro‐Prins rearrangement sequence from (−)‐(R)‐campholenyl acetate((−)‐4) opens a new access to the naturally occurring (−)‐(R, R)‐β‐necrodol ((−)‐1) and its three stereoisomers with high optical purity.
Highly Regioselective Nitration of Hexamethylbenzene and Its Derivatives to Dinitroprehnitene with Excess Nitronium Tetrafluoroborate
Authors: Surya Prakasb G. K. , Wang Qi , Li Xing‐Ya , Olah George A.
Published: December 2004

Hexamethylbenzene and its derivatives undergo very clean regioselective dinitration to dinitroprehnitene (1, 2, 3, 4‐tetramethyl‐5, 6‐dinitrobenzene) with excess of nitronium tetrafluoroborate in dry CH2C12 solution. The mechanism of this unexpected new nitration is also discussed.
Synthesis and Chemical Transformations of 4, 5‐Homosnoutene Derivatives: An Attempted New Access onto the (CH)12 Energy Hypersurface
Authors: Kirchmeyer Stephan , De Meijere Armin
Published: December 2004

Pentacyclo[6. 4. 02, 4. 03, 10. 07, 9]dodeca‐5, 11‐diene(4) is proposed as new potential precursor of the truncated tetrahedrane 1. The synthesis of several new pentacyclo[5. 4. 0. 02, 4. 03, 9. 06, 8] undec‐10‐ene (4, 5‐homosnoutene) derivatives including homosnouten‐5‐one(10), 5‐methylidenehomosnoutene(19a) as well as homosnoutene‐5‐carb‐aldehyde(17b) and their reactions directed toward ring enlargement to the skeleton of 4 are reported. Although all the homosnoutenes resisted ring expansions, several unexpected new polycyclic systems were obtained. Any intermediate developing a cationic center at C(5) of the skeleton of 10 rearranged with release of strain and opening of one or both three‐membered rings to give compounds such as 22 and 23. The aminomethyl derivatives 13a and 13b, upon diazotation, underwent a remarkable fragmentation to give 10 and homosnouten‐5‐o1(20), respectively. The 5‐(dibromomethyl) homosnouten‐5‐o1(14), upon treatement with t‐BuLi, rearranged to the pentacyclic ether 15, while the carbine 11b, generated by the thermal or photochemical decomposition of the tosylhydrazone salt of 17c, solely gave 19a by C, H insertion. The 1, 1‐dicyclopropylethene unit in 19c was excited selectively upon irradiation, but the products 26 and 27 of this photochemical rearrangement were derived only from n‐participation in diradical intermediates 25a‐25c.
Electronic and Steric Influence of Axial and Equatorial Ligands in Vitamin B12 Model Complexes Derived from Cobaloxime: Electrochemical and 59Co‐NMR Studies
Authors: Tavagnacco Claudio , Balducci Gabriele , Costa Giacomo , Täschler Karl , von Philipsborn Wolfgang
Published: December 2004

In four series of strictly related organocobalt complexes, derived from cobaloximes by replacement of the O…H…O with O…‐BF2…O and/or (CH2)3 groups, the trends of 59Co‐NMR shielding and electrochemical data are discussed. A largely parallel behaviour of the plots of E1/2(I) values for the first Co(III)/Co(II) electron transfer vs. the 59Co chemical shifts reflects the similar sensitivity of the two parameters to a change in electron affinity of the central metal ion due to a variation of the organic group R. E1/2(II) values for the second Co(II)/CO(I) electron transfer are less sensitive to the change of R, but the trend of the plot vs. δ(59Co) is still parallel in the four series. Consistent deviations from a roughly linear dependence of E1/2(I) on pKa of the hydrocarbon acid corresponding to R, on Taft constant s̀* and on 59Co shielding are noticed for the isopropyl derivatives and attributed to a steric effect. This was confirmed in a series of RCo(DMG)pyridine complexes in which 59Co shielding decreases steadily with increasing steric parameter Es (Taft) of the alkyl group. There is experimental evidence from X‐ray data that δ(59Co) decreases with an increase of the CoC bond length, illustrating steric hindrance in alkyl coordination to be responsible for the decreased shielding of the 59Co nucleus. The relative displacements of the graphic displays for the different series reflect the effect of changes in electron affinity of the redox center, due to the equatorial ligand, which, in turn, is caused by variations in the electron‐withdrawing power due to the introduction of the BF2 group and by the change from −2 to −1 valence of the (CH2)3‐capped ligands.
Synthesis of Cationic 2,4‐Dimethylpenta‐2,4‐dienylruthenium Complexes. Crystal Structure of Carbonyl(η4‐cyclohexa‐1,3‐diene)‐(η5‐2,4‐dimethylpenta‐2,4‐dienyl)ruthenium Tetrafluoroborate
Authors: Lumini Tito , Cox David N. , Roulet Raymond , Chapuis Gervais , Nicolo Francesco
Published: December 2004

The complex [Ru(η5‐C7H11)2H]BF4 (C7H11 = 2,4‐dimethylpenta‐2,4‐dienyl) is highly reactive towards two‐ and six‐electron ligands. e.g. giving with CO complex [RuCO(η4‐C7H12)(η5‐C7H11)]BF4. The 2,4‐dimethylpenta‐1,3‐diene ligand (C7H12) of the latter complex is readily displaced giving, e.g. with excess cyclohexa‐1,3‐diene (C6H8) complex [RuCO(η4‐C6H8)(η5‐C7H11)]BF4. These reactions provide a convenient entry into monopentadienylruthenium chemistry.
Kinetic and thermodynamic parameters for Schiff‐rase formation between 5′‐deoxypyridoxal and hexylamine
Authors: Vazquez Miguel A. , Donoso Josefa , Muñoz Francisco , Blanco Francisco Garcia , del Vado M. Angeles Garcia , Echevarria Gerardo
Published: December 2004

The thermodynamic parameters involved in the formation of Schiff bases between 5′‐deoxypyridoxal and hexylamine were determined at different pH values and a constant ionic strength (0.1 M). The overall and individual rale constants of formation and hydrolysis at 10, 15, 20, 25, and 30° were also determined. The enthalpy of the overall formation process was found to be negative at all the pH values assayed except the neutral, while its entropy was always positive. The results obtained show the great relevance of the phosphate group at C(5′) to the stabilization of the Schiff bases of pyridoxal 5′‐phosphate.
Studies Directed Towards the Biosynthesis of the C7N Unit of Rifamycin B: A New Synthesis of Quinic Acid from Shikimic Acid
Authors: Meier Rose‐Marie , Tamm Christoph
Published: December 2004

The synthesis of quinic acid (4) via epoxide 13, starting from shikimic acid (5), is described (Scheme 1). Treatment of 13 with thiophenol yielded not only 17, but also the γ‐lactones 18 and 19 as result of migration of silyl groups within a cis‐ and trans‐diol system. The conversion provides a direct stereoselective epoxidation of a shikimic‐acid derivative as well as an alternative pathway for the preparation of 4. A shorter approach via the disilylated epoxide 22 was unsuccessful because the γ‐lactone 25 was obtained in place of the desired α‐hydroxy ester 24 (Scheme 2).
Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)‐3,6:3′,6′‐Diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotin‐5,5′‐diol), ein neues Carotinoid aus Paprika (Capsicum annuum)
Authors: Deli Jóseph , Mólnar Péter , Tóth Gyula , Baumeler Andreas , Eugster Conrad Hans
Published: December 2004

Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)‐3.6:3′,6′‐Diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐5,5′‐diol), a Novel Carotenoid from Red Paprika (Capsicum annuum)

From red paprika (Capsicum annuum var. longum nigrum) cycloviolaxanthin was isolated as a minor carotenoid and, based on spectral data, assigned the symmetrical structure 8.
Double‐Diamond Inclusion Compounds of 2,6‐Dimethylydeneadamantane‐1,3,5,7‐tetracarboxylic Acid
Authors: Ermer Otto , Lindenberg Lorenz
Published: December 2004

The crystal structures of four inclusion compounds of 2,6‐dimethylideneadamantane‐1,3,5,7‐tetracarboxylic acid (4) are described, which involve the following guest species: (a) a mixture of 4‐methylpent‐3‐en‐2‐one, 2,6‐dimethylhepta‐2,5‐dien‐4‐one, and mesitylene (condensation products of acetone); (b) mesitylene; (c) a mixture of 4‐methylpent‐3‐en‐2‐one and mesitylene; (d) (tert‐butyl)benzene. In all four cases, the host architectures consist of two interpenetrating super‐diamond networks built up by the tetra‐acid molecules via pairwise H‐bonds between the tetrahedrally directed COOH groups. In the first three cases (tetragonal crystal symmetry), the two diamond‐like host lattices interpenetrate symmetrically, in the fourth case (monoclinic) asymmetrically. This asymmetry is brought about by the increased steric bulk of the (tert‐butyl)benzene guest molecules. Attempts to enforce an inclusion compound of 4 with a single, extremely hollow diamond‐like host lattice by offering still bulkier guest molecules have as yet not been met with success. The generally very high propensity of 4 to form inclusion compounds was envisaged and designed beforehand by appropriate evaluation and modulation of the crystal structure of the parent adamantane‐1,3,5,7‐tetracarboxylic acid, which represents a fivefold diamond‐like self‐inclusion compound. Crystals of the free, uncomplexed 4 appear to be extremely unstable and could so far not be obtained. On the other hand, from aqueous solution a very stable monohydrate of 4 may be crystallized (4‐H2O), which was also subjected to X‐ray analysis. The (triclinic) crystal structure of 4·H2O involves an interesting dichotomy inasmuch its pattern of H‐bonding may be rationalized either in terms of a double, cross‐linked super‐zincblende (sphalerite) architecture, or as a system of porous, puckered 4‐connected sheets, which interpenetrate each other pairwise and are cross‐linked by the H2O molecules. Various structure and (space group) symmetry characteristics of the supramolecular solid‐state complexes reported here are highlighted by pointing out analogies with comparable structures retrieved from the literature.
Ruthenium(II) Complex of the Alkaloid 2‐Bromoleptoclinidinone. Preparation and Interaction with Double‐Stranded DNA
Authors: Goullc Véronique , Lehn Jean‐Marie , Schoentjes Bruno , Schmitz Francis J.
Published: December 2004

The fused pentacyclic alkaloid 2‐bromoleptoclinidinone (1) isolated from an ascidian possesses a bidentate chelating site. Complexation of 1 with [cis‐RuCl2{(D8)bpy}2] · 2H2O forms an octahedral complex which was isolated both as hexafluorophosphate 2 and chloride 3 salts. Intercalation of 3 in calf‐thymus DNA was shown to occur as well as photoactivated cleavage of double‐strand supercoiled DNA pBR322 under visible‐light irradiation.
1,3‐Oxathiolan‐Synthese: Spirocyclische 1,3‐Oxathiolane aus der Lewis‐Säure‐katalysierten Umsetzung von cyclischen Trithiocarbonaten und Oxiranen
Authors: Oremus Vladimir , Linden Anthony , Heimgartner Heinz
Published: December 2004

1,3‐Oxathiolanc Synthesis: Spirocyclic 1,3‐Oxathiolanes from the Lewis‐Acid‐Catalyzed Reaction of Cyclic Trithiocarbonates and Oxiranes

The cyclic trithiocarbonates 1.3‐dithiolane‐2‐thione (4) and 1,3‐dithiole‐2‐thione (9) in 1,2‐dichloroethane and MeCN, respectively, react with alkyl‐ and phenyl‐substituted oxiranes 2 in the presence of Lewis acids to give 1‐oxa‐4,6,9‐trithiaspiro[4.4]nonanes 5 and 6 (Scheme 2) and 1‐oxa‐4,6,9‐trithiaspiro[4.4]non‐7‐enes 10 and 11 (Scheme 3), respectively. The reactions proceed regioselectively yielding 2‐alkyl (5, 10) and 3‐phenyl derivatives (6, 11) as the main products. From the reaction of 4 and 2‐phenyloxirane (2e) with TiCl4, 2‐phenyl‐1,4,6,9‐tetrathia‐spiro[4.4]nonane (7) is isolated as a minor product. The molecular structures of 5a, 6e, and 7 are established by X‐ray crystallography.
SN2 or Electron Transfer?? A new technique discriminates the mechanisms of oxidative addition of alkyl halides to corrinato‐ and porphyrinatocobalt(I)
Authors: Zhou De‐Ling , Walder Peristera , Scheffold Rolf , Walder Lorenz
Published: December 2004

A fast electrochemical technique for the discrimination of one‐ and two‐electron mechanisms in the oxidative addition of alkylating agents (RX) to corrinato‐ and porphyrinatocobalt(I) ([CoIL]) is described. It is based on single‐scan voltammograms of [CoIIL] in the presence of RX and variable amounts of the radical trap acrylonitrile. In the first part of the voltammogram, [CoIIL] is reduced, and fast oxidative addition of RX to [CoIL] is triggered. If the reaction proceeds via a two‐electron mechanism, [RCoIIIL] is formed independently of acrylonitrile concentration, but if a transient free radical R is involved, R is competitively trapped by acrylonitrile and [CoIIL] to yield, at high enough acrylonitrile concentration, exclusively the olefin‐inserted [RCNCoIIIL]. [RCNCoIIIL] is reducible in the intermediate potential range, [RCoIIIL] at the negative end of the single‐scan voltammogram. Hence, from the appearance of the reduction waves due to [RCNCoIIIL] and [RCoIIIL], the mechanism of oxidative addition of RX to [CoIL] is easily deduced. The method is applied to the study of the mechanistic borderline of oxidative addition using a series of 15 RX and 4 [CoL]'s, i.e. cobalamin (Cbl), heptamethyl cobyrinate (‘Cby’), (tetraphenylporphyrinato) cobalt ([Co(tpp])), and (octaethylporphyrinato) cobalt ([Co(oep)]). All non‐activated primary alkyl iodides and bromides exhibit, at room temperature, pure two‐electron mechanisms with all [CoIL]'s, except neopentyliodide with Cb1I and ‘Cby’I. All secondary alkyl iodides involve free radicals with Cb1I and ‘Cby’I, but a pure two‐electron mechanism or a mixed one‐electron two‐electron mechanism with [CoI(tpp)] and [CoI(oep)]. The mechanistic switch from a two‐electron to a one‐electron mechanism for increasingly sterically demanding RX's occurs earlier with the supernucleophilic Cb1I and ‘Cby’I than with [CoI(tapp)] and [CoI(oep)].
Axially Dissymmetric diphosphines in the Biphenyl Series: Crystal structures of three new group‐VIII metal complexes of (6,6′‐dimethyl‐1,1′‐biphenyl‐2,2′‐diyl)bis(diphenylphosphine) ( = biphemp)
Authors: Knierzinger Andreas , Schönholzer Peter
Published: December 2004

(6,6′‐Dimethyl‐1,1′‐biphenyl‐2,2′‐diyl)bis(diphenylphosphine) ( = biphemp) reacts with allymetal halidesm to yeild complexes 1–3 which were transformed into the corresponding perchlorates 4–6. The molecular structures of 4–6 were determined by X‐ray analyses.
Synthesis and Properties of Macrobicyclic Cryptates Incorporating Five‐ and Six‐Membered Biheteroaryl Units
Authors: Lehn Jean‐Marie , De Vains Jean‐Bernard Regnouf
Published: December 2004

The socium cryptates of the macrobicyclic ligands 1–6 have been synthesized by direct macrobicyclisation or by stepwise procedures. They incorporate 2,2′‐bithiazole, 2,2′‐biimidazole, 2.2′‐bipyrimidine as well as 2,2′‐bipyridine units. Treatment of the sodium complexes with europium(III) chloride gave the corresponding EuIII cryptates. The structural and spectral properties of these compounds are described. The EuIII complexes present characteristic 1H‐NMR chemical‐shift features. Their luminescence properties are described.
A Short Syntheses of 1,2‐Dimethylazulenes
Authors: Fallahpour Reza Ali , Hansen Hans‐Jürgen
Published: December 2004

Dimethyl azulene‐1,2‐dicarboxylates are reduced with a 4–5 molar excess of DIBAH in Et2O/hexane at 0° to yield the corresponding 2‐(hydroxymethyl)‐1‐methylazulenes which can be further reduced to 1,2‐dimethylazulenes on treatment with Et3SiH in TFA at 60° (cf. the Table).
Synthesis of Phosphonates and Oligodeoxyribonucleotides Derived from 2′‐Deoxyisoguanosine and 2′‐Deoxy‐2‐haloadenosines
Authors: Seela Frank , Mertens Ralf , Kazimierczuk Zygmunt
Published: December 2004

Oligonucleotides containing 2′‐deoxyisoguanosine (1) or 2‐chloro‐2′‐deoxyadenosine (2a) have been prepared by solid‐phase synthesis. Suitably protected phosphonates 3a, 4a, and 4b as well as the phosphoramidite of 1 have been obtained from the nucleosides 1, 2a, or 2b via the (dimethylamino)methylidene derivatives 5–7. 4,4′‐Dimethoxytrityl groups were introduced to yield the base‐protected derivatives 8–10. Alternatively to the direct incorporation of 1 into oligonucleotides, they were also obtained by the photochemical conversion of a 2a residue within the oligonucleotide chain.
Total Synthesis of the Gastroprotective Substance AI‐77‐B and of Analogues
Authors: Durgant Jean‐Marc , Vogel Pierre
Published: December 2004

The Diels‐Alder adducts 8 of furan to 1‐cyanovinyl acetate were converted into (Methyl 3‐chloro)‐5‐O‐(3‐chlorobenzoyl)‐2, 3‐dideoxy‐α‐dl‐arabino‐hexofuranosid)uronic acid ((α)‐18a) and into (methyl 3‐azido‐5‐O‐(3‐chlorobenzoyl_‐2,3‐dideoxy‐α‐dl‐ribo‐hexofuranosid)uronic acid ((α)‐41a). These compounds were condensed to (3S)‐3‐[(1′S)‐1′‐amino‐3′‐methylbutyl]‐3,4‐dihydro‐8‐hydroxyisocoumarin hydrochloride ((−)‐2); the resulting mixtures of diastereoisomeric amides were transformed and separated to give the gastroprotective substance AI‐77‐B((−)‐1) and analogues.
C2‐Symmetrical Pyrrolidine Derivatives Chiral Auxiliaries in Radical Chemistry
Authors: Veit Andres , Lenz Roman , Seiler Martin E. , Neuburger Markus , Zehnder Margareta , Giese Bernd
Published: December 2004

Fumaramides 3b and 3c bearing the C2‐symmetrical pyrrolidine moieties (2R,5R)‐2,5‐bis(methoxymethyl)pyrrolidine (2b) or 1,3:4,6‐di‐O‐benzylidene‐2,5‐dideoxy‐2,5‐imino‐L‐idit (2c), respectively, as a chiral auxiliary lead to high diastereoselectivities in radical reactions (‘tin method’;Scheme 1). Removal of the chiral auxiliaries affords the corresponding alkylated fumaric acids Scheme 2. Single‐crystal X‐ray structures of 3b and 3c support arguments that lead to the model of 1,4‐stereoinduction.
Nucleic‐Acid Analogues with Constraint Conformational Flexibility in the Sugar‐Phosphate Backbone (‘Bicyclo‐DNA’). Part 1. Preparation of (3S,5′R)‐2′‐Deoxy‐3′,5′‐ethano‐αβ‐D‐ribonucleosides (‘Bicyclonucleosides’)
Authors: Tarköy Markus , Bolli Martin , Schweizer Bernd , Leumann Christian
Published: December 2004

We describe the synthesis of 2′‐deoxy‐3′,5′‐ethano‐D‐ribonucleosides 1–8 (= (5′,8′‐dihydroxy‐2′‐oxabicyclo‐[3.3.0]oct‐3′‐yl)purines or ‐pyrimidines) of the nucleobases adenine, thymine, cytosine, and guanine. They differ from natural 2′‐deoxyribonucleosides only by an additional ethylene bridge between the centers C(3′) and C(5′). The configuration at these centers (3S,5′R) was chosen as to match the geometry of a repeating nucleoside unit in duplex DNA as close as possible. These nucleosides were designed to confer, as constituents of an oligonucleotide chain, a higher degree of preorganization of a single strand for duplex formation with respect to natural DNA, thus leading to an entropic advantage for the pairing process. The synthesis of these ‘bicyclonucleosides’ was achieved by construction of an enantiomerically pure carbohydrate precursor 18/19 (Schemes 1), which was then converted to the corresponding nucleosides by known methods in nucleoside synthesis (Schemes 2 and 3). In all cases, both anomeric forms of the nucleosides were obtained in pure crystalline form, the relative configuration of which was established by 1H‐NMR‐NOE spectroscopy. A conformational analysis of the nucleosides with β‐configuration at the anomeric center by means of X‐ray and 1H‐NMR (including NOE) spectroscopy show the furanose part of the molecules to adopt uniformly a 1′exo‐conformation with the base substituents preferentially in the anti‐range in the pyrimidine nucleosides (anti/syn ca. 2:1) distribution in the purine nucleosides (in solution).
C‐Alkylation of Sarcosine Residues in Cyclic Tetrapeptides via Lithium Enlates
Authors: Miller Scott A. , Griffiths Sian L. , Seebach Dieter
Published: December 2004

The cyclic tetrapeptides cyclo(‐Leu‐Sar‐Gly‐), cyclo(‐Val‐Sar‐Sar‐Gly‐), and cylco(‐Meleu‐Gly‐D‐Alasar‐) have been synthesized from the component amino acids (BOP‐Cl coupling), using the pentafluorophenyl esters for the cyclization step (42, 13, and 30% yield, respectively). Multiple deprotonation (LDA in THF/LiBr/DMPU) and addition of highly reactive electrophiles (CF3CO2D, MeI, CH2O, CH2CHCH2Br, PhCH2Br) produce cyclic tetrapeptides with additional substituents introduced diastereoselectively (70 to > 98% ds) in yields ranging from 20 to 90%. The C‐alkylatd products are all derived from a sarcosine‐enolate moiety adjacent to another N‐methylamino acid. The structures of the resulting products are determined by NMR spectroscopy (DNOE and ROESY techniques) and by hydrolysis to the parent amino acids, suitable derivatization, and analysis by chromatography on a chiral GC column. It was shown in two cases that the overall yield of cyclization/alkylation to give a disubstitued cyclic tetrapeptide is higher than that of a synthesis of the same product from the corresponding amino‐acid building blocks. Surprising temperature and salt effects on the yields and selectivities of the reactions of the cyclic tetrapeptide enolates are presented, and possible mechanistic interpretations are discussed.
Absolute Configuration of 2‐Substituted 2‐Azabicyclo[2.2.1]hept‐5‐enes
Authors: Pombo‐Villar Esteban , Boelsterli Jakob , Cid Maria Magdalena , France Julien , Fuchs Beat , Walkinshaw Malcolm , Weber Hans‐Peter
Published: December 2004

The diastereoisomeric 2‐substituted 2‐azabicyclo[2.2.1]hept‐5‐enes 2–4 were prepared by aza‐Diels‐Alder reaction of cyclopentadiene with the corresponding methaniminium ions. Their relative configurations were deduced using 1H, 1H‐ROESY experiments, and their absolute configurations were assigned from the crystal structure of the aziridinium derivative (−)‐5. The absolute configuration of (+)‐1, i.e. (1R), was assigned by CD spectroscopy.
Photoisomerization of 2H,6H‐thiin‐3‐one 1‐oxides to 3H,7H‐[1,2]oxathiepin‐4‐ones
Authors: Kowalewski Ronald , Margaretha Paul
Published: December 2004

Oxidation of 2H, 6H‐thiin‐3‐ones 1a–c with 3‐chloroperbenzoic acid affords the corresponding 1‐oxides 2a–c. On irradiation (350 nm) in either benzene or MeCN, these cyclic sulfoxides 2 isomerize to 3H, 7H‐1,2‐oxathiepin‐4‐ones 3. The tetramethyl derivative 3a is isolated by flash chromatography at −10°, but, at higher temperatures, it undergoes ring contraction and H2O elimination to give 4,4‐dimethyl‐2(2‐methylprop‐2enylidene)thietan‐3‐one (4). Diemthyloxathiepinones 3b and 3c undergo ring contraction in MeOH to afford 1‐(4‐methylthiophen‐2‐yl)ethanone (5) and two diastereoisomeric 4,4‐dimethyl‐2‐methoxy‐2‐(1‐methoxyethyl)thietan‐3‐ones (6 and 7, respectively).
Palladium‐Catalyzed ‘Metallo‐Ene’‐Type Cyclization/Vinylstannane Coupling of 1‐Acetoxy‐octa‐2,7‐dienes and 1‐Acetoxy‐oct‐2‐en‐7‐ynes
Authors: Oppolzer Wolfgang , Ruiz‐Montes José
Published: December 2004

Palladiumbis(dibenzylideneacetone)/tri(2‐furyl)phosphine‐catalyzed cyclizations of dienyl acetates 2 in the presence of an (1‐alkenyl)(tributyl)stannane and ZnCl2 provided trans‐substituted 3‐alkenyl‐4‐vinylcyclopentanes 11 in good yields. Analogous intramolecular carbometallation/C,C‐coupling of enynyl acetates 4, 6, and 8 furnished, stereospecifically, monocylic trienes 19, 20, and 21, respectively.
Synthesis and Ruthenium‐Catalyzed Enantioselective Hydrogenation of 3‐O‐Substituted 1,3‐Dihydroxypropan‐2‐ones. Part 2
Authors: Cesarotti Edoardo , Antognazza Patrizia , Pallavicini Marco , Villa Luigi
Published: December 2004

A number of 3‐O‐substituted 1,3‐dihydroxypropan‐2‐ones have been synthesized in view of their potential use as prochiral precursors of optically active glycerols. Indeed, the oxo‐ethers have been reduced to the corresponding 3‐O‐substituted glycerols via chiral Ru complexes derived from (S)‐binap, ( =(−)‐(S)‐2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthalene) with enantiomeric excesses up to 93%. The steric course of the catalytic reduction appears to be essentially dependent on the steric encumbrance of the substituents; indeed, a dramatic increase of the enantiomeric excess is observed when the bulky trityl group is substituted by the less encumbering benzyl or octadecyl groups.
Molecular Geometries by the Extended‐Hückel Molecular Orbital Method III: Band‐structure calculations
Authors: Brändle Martin , Calzaferri Gion
Published: December 2004

Geometries of extended structures can be evaluated with the extended‐Hückel tight‐binding method by inclusion of a distance‐dependent weighted Wolfsberg‐Helmholz formula and an approximate two‐body electrostatic repulsive‐energy term. We explain the theoretical procedure which is shown to be straightforward. Application to (all‐trans)‐polyacetylene yields alternating C, C bond lengths and a bandgap of 1.6 eV at the optimized geometry, in good agreement with the experimental finding.
Refined Insight in Stereochemical and Directional Features of the FeI‐Mediated Dehydrogenation of Tetralin
Authors: Seemeyer Katrin , Schwarz Helmut
Published: December 2004

Experimental results demonstrate that, in the course of gas‐phase Fe+‐mediated dehydrogenation of tetralin, the metal ion sticks to the same plane of the hydrocarbon surface. The study of 5‐substituted, labeled tetralin analogues reveal the operation of an interesting substituent effect: Steric hindrance imposed by a CH3 group at C(5) deflects the metal to the more easily accessible region of C(1)/C(2); in contrast, a CH3O substituent at C(5) directs the metal ion to the more congested C(3)/C(4) region which clearly points to a coordination of Fe+ to the MeO group in the course of the haptotropic migration.
Synthesen und Untersuchungen von [Oxazolo[2,3‐a]isoindol‐9b(2H)‐yl]phosphonaten und ‐phosphinaten: Eine neue Klasse von Heterocyclen
Authors: Neidlein Richard , Greulich Peter , Kramer Walter
Published: December 2004

Syntheses and Investigations of [Oxazolo[2,3‐a]isoindol‐9b(2H)‐yl]phosphonates and ‐phosphinates: a New Class of Heterocycles

We attempted to synthesize diethyl (1‐methyl‐2‐phthalimidoethyl)phosphonate (14a) in a Michaelis‐Becker reaction using diethyl sodiophosphonate (13) and the tosylate 12a of (2‐hydroxypropyl)phthalimide as starting materials. Instead of TsO substitution in 12a by the nucleophile 13, the carbonyl C‐atom of the phthalimido moiety was attacked by 13, followed by an intramolecular nucleophilic substitution at C(2) of the side chain leading to the (oxazolo[2,3‐a]isoindolyl)phosphonate 15a (Scheme 1). Similarly, 12a and N‐(2‐bromoethyl)phthalimide (12b) reacted with butyl (benzene)sodiophosphinate (18) to the (oxazolo[2,3‐a]isoindolyl)(phenyl)phosphinates 20a and 20b, respectively (Scheme 2). The attempt to synthesize enantiomerically pure 2‐substituted (2‐phthalimidoethyl)phosphonates 27 starting from L‐α‐amino‐acids failed, too (Scheme 3): the main products of the reaction of the N,N‐phthaloyl‐O1‐tosyl‐L‐aminoalcohols 25a–d with 13 were the 3‐substituted (oxazolo[2,3‐a]isoindolyl)‐phosphonates 26a–d, the desired 27b and 27c being observed as by‐products in the 31P‐NMR spectrum.
Syntheses of the First Selenium‐Containing Bicyclic β ‐Lactams as Potent Antimicrobial Agents
Authors: Hwu Jih Ru , Lai Long‐Li , Hakimelahi Gholam H. , Davari Hady
Published: December 2004

Syntheses of the cis‐configurated isodethiaselenapenam 5 (Scheme 1) as well as the isodethiaselenacephems 29 and 31 (Scheme 2) were accomplished, in which the key step involved addition of Se to the corresponding carbanions of 1, 25, and 27 followed by internal alkylation. β‐Lactams 29 and 31 were found to possess biological activity against several pathogenic microorganisms in vitro. The electronic activation of the lactam moiety in the isodethiaselenacephem 31 and the corresponding isocephem 33 remarkably enhanced their biological activity. Isodethiaselenacephem 31 was more toxic than isocephem 33 in experimental animals.
β‐Peptides: Synthesis by Arndt‐Eistert homologation with concomitant peptide coupling. Structure determination by NMR and CD spectroscopy and by X‐ray crystallography. Helical secondary structure of a β‐hexapeptide in solution and its stability towards pepsin
Authors: Seebach Dieter , Overhand Mark , Kühnle Florian N. M. , Martinoni Bruno , Oberer Lukas , Hommel Ulrich , Widmer Hans
Published: December 2004

The β‐hexapeptide (H‐β‐HVal‐β‐HAla‐β‐HLeu)2‐OH (2) was prepared from the component L‐β‐amino acids by conventional peptide synthesis, including fragment coupling. A cyclo‐β‐tri‐ and a cyclo‐β‐hexapeptide were also prepared. The β‐amino acids were obtained from α‐amino acids by Arndt‐Eistert homologation. All reactions leading to the β‐peptides occur smoothly and in high yields. The β‐peptides were characterized by their CD and NMR spectra (COSY, ROESY, TOCSY, and NOE‐restricted modelling), and by an X‐ray crystal‐structure analysis. β‐Sheet‐type structures (in the solid state) and a compact, left‐handed or (M) 31 helix of 5‐Å pitch (in solution) were discovered. Comparison with the analogous secondary structures of α‐peptides shows fundamental differences, the most surprising one at this point being the greater stability of β‐peptide helices. There are structural relationships of β‐peptides with oligomers of β‐hydroxyalkanoic acids, and dissimilarities between the two classes of compounds are a demonstration of the power of H‐bonding. The β‐hexapeptide 2 is stable to cleavage by pepsin at pH 2 in H2O for at least 60 h at 37°, while the corresponding α‐peptide H‐(Val‐Ala‐Leu)2‐OH is cleaved instantaneously under these conditions. The implication of the described results are discussed.
Lipase‐Catalysed Regioselective Deacetylation of androstane derivatives
Authors: Baldessari Alicia , Bruttomesso Andrea C. , Gros Eduardo G.
Published: December 2004

A series of acetoxy derivatives of androstane was deacetylated in organic solvents by several lipases. The most satisfactory results were obtained with lipase from Candida cylindracea (CCL) and Candida antarctica (CAL). In some derivatives, CCL and CAL showed an overwhelming regioselectivity towards the removal of the 3β‐ or the 17β‐acetyl group (see Table 2). Three new steroid derivatives were obtained through this approach. A hypothetical rationale for the behaviour of these enzymes is given.
Synthesis and Characterization of the (5′ → 5″)‐Ester of Adenosine 5′‐diphosphate with α‐D‐ribofuranose cyclic 1″,2″‐phosphate: A NAD derivative produced during tRNA splicing
Authors: Hall Jonathan , Genschik Pascal , Filipowicz Witold
Published: December 2004

The synthesis and spectroscopic properties of the (5′ → 5″)‐ester of adenosine 5′‐diphosphate with ribofuranose cyclic 1″, 2″‐phosphate 3, a recently discovered metabolite produced during tRNA splicing, are reported.
Nucleotides. Part XLVIII. Synthesis of 2′‐amino‐2′‐deoxyarabinonucleoside phosphoramidite building blocks
Authors: Walcher Gunter , Pfleiderer Wolfgang
Published: December 2004

Chemical syntheses of 2′‐amino‐2′‐deoxyarabinonucleosides of uracil, thymine, cytosine, adenine, and guanine and their conversion into suitably protected 3′‐phosphoramidite building blocks 24–28 for oligonucleotide synthesis are described. The 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) group was used for protection of the aglycon and the 2′‐amino functions.
Tripodal Dodecadentate Ligands with Salicylamide and bipyridine binding sites for iron(II) and iron(III) coordination
Authors: Lutz Andreas , Ward Thomas R.
Published: December 2004

The synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.
Synthesis of a Ketorolac Model via Aromatic Carbenoid Insertion
Authors: Müller Paul , Polleux Philippe
Published: December 2004

The decomposition of diazo ester 2b with chiral RhII catalysts proceeded via intramolecular aromatic carbenoid insertion to the racemic pyrrole derivative 5b in 72% yield. In contrast, the benzoylated precursor 16 afforded no ketorolac 1b when exposed to RhII. Methyl 2‐diazo‐4‐phenylbutyrate (19), in turn, reacted, by 1,2‐hydrogen migration rather than by aromatic substitution, to 20.
Etudes sur les matières végétales volatiles XXXVI. Présence d'époxylinalol dans les huiles essentielles
Authors: Naves Y. R.
Published: December 2004

L'époxylinalol libre ou estérifié existe dans l'essence de lavandin, libre dans l'essence de shiu. L'acétate d'époxylinalyle est séparé quantitativement des esters acétiques des alcools satellites au moyen de son complexe hexacyanoferrique(II).
Zur Krystallstruktur des p,p′‐Dichlordiphenyl‐trichlor‐äthan
Authors: Wild H. , Brandenberger E.
Published: December 2004

1. p,p′‐Dichlordiphenyl‐trichlor‐äthan krystallisiert in der orthorhombisch‐hemimorphen Klasse C2v und zwar mit C—Pbc als wahrscheinlichem Raumsystem.
Recherches sur l'électrolyse avec le courant ondulé. IV. Observations sur le comportement des anodes de platine poli dans l'électrolyse de solutions utilisées en vue de la préparation du perborate
Authors: Briner E. , Löwy E.
Published: December 2004

Faisant suite aux recherches précédentes sur la production de l'ozone par électrolyse de solutions d'acide sulfurique avec du courant ondulé, on a étudié — toujours en utilisant des électrodes de platine poli — la formation d'oxygène actif dans des solutions alcalines de composition propre à la préparation de perborate.
Über eine neue l‐Aminosäure‐oxydase (Ophio‐l‐aminosäure‐oxydase). 2. Mitteilung
Authors: Zeller E. A. , Maritz A.
Published: December 2004

1. Auf verschiedene Weise konnte gezeigt werden, dass in den Giften von Naja, Bothrops atrox, Vipera aspis, Vipera latastei und Vipera libetina das in der ersten Mitteilung als Ophio‐l‐aminosäure‐oxydase (Ophio‐oxydase) bezeichnete Ferment auftritt. Geringe Unterschiede gehen nicht über die auch sonst bei Fermenten bekannten artspezifischen Eigentümlichkeiten hinaus.
Zur percutanen Resorption lipoidlöslicher Substanzen aus organischen Lösungsmitteln
Authors: Stadlin Walter
Published: December 2004

1. In Aceton und Wasser aa gelöstes Oestron bewirkt bei Auftropfen auf die Nackenhaut des Meerschweinchens eine erhebliche Vergrösserung der Zitzen.
Über Vinylchlorid und seine Polymerisationsprodukte. I. Zur Kenntnis von Polyvinylchlorid
Authors: Fierz‐Davie H. E. , Zollinger Hch.
Published: December 2004

1. Der direkte oxydative Abbau von Polyvinylchlorid liefert keine zur Konstitutionsbestimmung brauchbaren Resultate.
Über den Aufbau von Viskosefasern mit Mantelbildung
Authors: Wuhrmann K.
Published: December 2004

Die quantitative optische Untersuchung von Viskosefasern mit Mantelbildung ergibt, dass in Übereinstimmung mit früheren qualitativen Beobachtungen die Mantelzonen bedeutend höhere Doppelbrechungswerte aufweisen als die Faserkerne.
Hydrogen bonding in simple π‐electron systems I. Pyridinium–pyridine
Authors: Sabin John R.
Published: December 2004

In this work, the application of the Pariser–Parr–Pople scheme to hydrogen‐bonded systems containing π electrons has been examined. The potential energy curves for the movement of the hydrogen atom in the bond have been calculated, and the reliability of the results obtained from this method, applied in this manner, have been discussed.
The ground state of atomic two‐electron systems in the independent particle model
Authors: Hoor Marten J. Ten
Published: December 2004

Scaled variational functions of the form \documentclass{article}\pagestyle{empty}\begin{document}$ \phi _{\alpha k} = e^{ - (Z - 1 + e^{ - \alpha kr})kr} $\end{document}, where Z is the nuclear charge and α is a parameter, and \documentclass{article}\pagestyle{empty}\begin{document}$ \phi _{\beta \alpha k} = e^{ - (\beta + e^{ - \alpha kr})kr} $\end{document}, where both α and β are parameters, are used for the description of the ground state of atomic two‐electron systems in the independent particle model. The scale factor k has been introduced in order to satisfy the virial theorem.

Apart from the energy, a number of one‐electron expectation values have been calculated and the results are compared with those obtained from other variational functions.

The function ϕαk yields already a good approximation to the Hartree–Fock solution whereas with the function ϕβαk the Hartree–Fock results are practically reproduced.
On the formulation of spin‐free quantum chemistry
Authors: Heldmann G.
Published: December 2004

A set of spin‐free functions ϕi(r),i = 1 …︁ f, is obtained which form the basis of spin‐free quantum chemistry. The ϕi(r) show a one‐to‐one correspondence to antisymmetric space‐spin functions Ψi(r, σ) with spin functions constructed according to Löwdin's projector operator method.
Coupling of equivalent particles in a field of given symmetry
Authors: Goscinski Osvaldo , Öhrn Yngve
Published: December 2004

A formula of Kotani for the coupling of equivalent particles in a field of a given symmetry is rederived using group algebraic methods.
Vibronic absorption spectrum of the ethylene dimer
Authors: Sadlej Andrzej J.
Published: December 2004

Vibronic coupling theory is used to construct the vibronic absorption spectrum of the ethylene dimer. It is shown that in this case an extended four‐parameter form of the vibronic Hamiltonian should be considered. In addition to the commonly used three vibronic parameters, the difference between the ground and excited state force constants of the monomer is taken into account.

Numerical calculations were performed for the dimer geometry resembling that of norbornadiene. Some comments on the interpretation of the absorption spectrum of norbornadiene are made.
Free‐electron model for electronic spectra of benzene
Authors: Sen Purnendranath , Basu Sadhan
Published: December 2004

Using a three dimensional free‐electron model for the π‐electron system the energies of the various singly and doubly excited configurations of benzene have been calculated. It has been found that the energies of the various singly excited configurations are in good agreement with the values obtained by Craig; whereas the energies of the doubly excited configurations are higher than those obtained by Craig. Therefore the configurational mixing for the doubly excited configurations is not necessary in this kind of model.
The hydrogen atom in a cubic field of electric dipoles
Authors: Blokker Esko
Published: December 2004

The full rotational symmetry of the hydrogen atom is lowered to that of the double group of Oh. This is done by a cubic field of electric dipoles. Symmetry‐adapted spin orbitals have been calculated and with them the energies of the lowest states as functions of the distance from the dipoles to the atom, the dipole moment, and the size of the atoms forming the dipoles. The Hamiltonian used is obtained by starting with the Dirac equations and then making some simplifications and approximations.
High orders corrections to the Van der Waals–London forces. II. Interaction of two molecules with isotropic polarizabilities
Authors: Malrieu J. P.
Published: December 2004

The infinite summation of intermolecular ring diagrams is extended to any pair of interacting molecules with isotropic polarizabilities. The calculation no longer requires the use of a minimal basis set. The polarizabilities α,α′ may be factorized at all orders, and an expression is derived, which gives modified Van der Waals energies. For heavy atoms the series converges if αα′/R6 is smaller than 1, R being the interatomic distance. This inequality is easily satisfied for the Van der Waals distances, and in practice the correction due to the high orders of the perturbation expansion remains weak. The role of the EPV diagrams and the connection with a configuration interaction treatment are discussed.
On the Mavroyannis–Stephen relativistic long‐range interaction energy term between optically active molecules
Authors: Chang Tai Yup
Published: December 2004

The relativistic long‐range intermolecular interaction energy term of Mavroyannis and Stephen is estimated for some amino acids by using optical rotatory dispersion data and for hexahelicene by using theoretical values of excitation energies and rotational strengths. The result shows that the interaction energy may be significant for the interaction between some essentially dissymmetric chromophores such as hexahelicene, but that it is unimportant for other cases.
Studies on Rydberg orbitals. IV. Basic formulas for the one‐electron perturbation calculation of molecular Rydberg excited states
Authors: Hosoya Haruo
Published: December 2004

General expressions are obtained for the energies of complex and real forms of any hydrogenic orbital (n, l, m) in a cluster of point charges of any geometry. This is a perturbation calculation of hydrogenic Rydberg orbitals in a one‐electron hard core approximation. A model calculation of 3d‐electrons of carbene, ethylene and benzene with varying charge distribution is given.
Quasi‐relativistic approximation in the SCF‐MO‐LCAO method
Authors: Bersuker I. B. , Budnikov S. S. , Leizerov B. A.
Published: December 2004

A quasi‐relativistic approach to the MO‐LCAO method is formulated taking into account the relativistic effects with an accuracy up to (v/c)2 terms, the relativistic part of the electronic interaction in the Hamiltonian being neglected. In the framework of this approximation a set of SCF equations of the Roothaan form is derived; here only the relativistic analogue to the closed shell systems with one‐determinant wave functions is considered. In so doing three types of relativistic corrections arise which are quite similar to those of the Pauli equation for one‐electron atoms. The new matrix elements appearing due to these corrections can be reduced to some common integrals, which have to be calculated with relativistic radial atomic functions. The method allows a semi‐empirical approach to the problem and does not require the Dirac four‐component atomic functions (unknown in the most cases), thus making possible approximate quasi‐relativistic electronic structure calculations of heavy‐atom compounds.