bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photochemische Reaktionen. 105. Mitteilung [1]. Zur Photochemie optisch aktiver λ, δ‐Epoxy‐enone: Racemisierung und Cyclisierung von (−)‐4‐Methyliden‐5,6‐epoxy‐5,6‐dihydro‐β‐jonon und (−)‐4‐Oxo‐5,6‐epoxy‐5,6‐dihydro‐β‐jonon
Authors: Frei Bruno , Wolf Hans Richard , Jeger Oskar 
Published: December 2004

The photochemistry of optical active λ, δ‐epoxy‐enones. Racemization and cyclization of (−)‐4‐methylidene‐5,6‐epoxy‐5,6‐dihydro‐β‐ionone and of (−)‐4‐oxo‐5,6‐epoxy‐5,6‐dihydro‐β‐iononeUV.‐irradiation (λ ≥ 347 nm as well as λ = 254 nm) converts the conjugated λ, δ‐epoxy‐enones (−)‐2 and (−)‐4 by cleavage of the C,C‐oxirane bond to an intermediate ketonium ylide f which cyclizes giving the racemic starting materials. The degree of racemization depends on the length of the irradiation time.The formation of the optical active products (−)‐3 and (+)‐5 in these irradiations gives evidence, that the photocyclization of (−)‐2 und (−)‐4, respectively, is a one step reaction of a state g.
Kinetics of Ethylene Oxidation on a Supported Silver Catalyst
Authors: Dettwiler Hans Rudolf , Baiker Alfons , Richarz Werner 
Published: December 2004

AbstractThe kinetics of ethylene oxidation by air over a supported silver catalyst were investigated in the temperature range 490–620 K. The reaction network was found to be triangular. Under virtually constant oxygen partial pressure (0.2 bar), the following rate relationships, (in mol g−1s−1) were found: (formulae in curved brackets denote partial pressures)
equation image
where
equation image
R is expressed in J · mol−1 · K−1.The given rate expressions are discussed in the framework of earlier kinetic investigations.
Polar Substituent Effects in the Solvolysis of Acyclic Tertiary Chlorides Polar Effects VI
Authors: Grob Cyril A. , Waldner Adrian 
Published: December 2004

AbstractThe influence of twenty substituents R on the solvolysis rates and products of tertiary chlorides R ‐ CH2CH2C(CH3)2Cl (7) has been studied. H, CH3, (CH3)2NCH2, ClCH2, Cl, CN and NO2 exert an inductive effect only, as the good correlation of the rates with the corresponding inductive substituent constants σ shows. Bulkier alkyl groups, i.e. isopropyl and t‐butyl, lower the rate due to a Baker‐Nathan effect, while the n‐electron donors CH3S, CH3O, HO and (CH3)2N and the σ‐electron donors (CH3)3Sn and HOCH2 cause rate increases based on σ constants. These accelerations are attributed to C,C‐hyperconjugative and inductomeric effects which arise in the transition state for ionization. A comparison of the reactivity of the acyclic chlorides 7 and the corresponding 1‐R‐substituted 3‐bromoadamantanes 1a shows that polar substituent effects are more strongly transmitted in the rigid bicyclic compounds 1a than in the flexible acyclic compounds 7.
Gilmaniellin and Dechlorogilmaniellin, Two Novel Dimeric Oxaphenalenones
Authors: Chexal Kuldip K. , Tamm Christoph , Hirotsu Ken , Clardy Jon 
Published: December 2004

AbstractThe structure and configuration of gilmaniellin, a metabolite of Gilmaniella humicola BARRON, has been shown to be 2 by X‐ray analysis. By comparison of spectral data structure 1 has been assigned to dechlorogilmaniellin.
Halogenation of Xanthenyl and Thioxanthenylallenes
Authors: Abdul‐Malik Nadia Fouad , Awad Sami Bassili , Sakla Afly Badie 
Published: December 2004

AbstractReactions of acids with vinylidenexanthenes (or thioxanthenes) 1 and 9‐methoxy‐9‐vinylxanthenes (or thioxanthenes) 8 give xanthene‐ (or thioxanthene‐) 9‐spiro‐1′‐indenes 7. With bromine or sulfuryl chloride they give the corresponding 2′‐halogenoxanthene‐ (or thioxanthene‐)9‐spiro‐1′‐indenes 5. Formation of such derivatives depends on preferential attack of the reagents on allenes 1 to give initially xanthylium (or thioxanthylium) ions 3 which cyclize. One π bond of the allenes 1 can be selectively reduced in acid media. Chemical and spectral evidence for these routes are presented.
1,3‐Dipolar Cycloadditions to Strained Olefins
Authors: Becker Konrad B. , Hohermuth Martin K. 
Published: December 2004

AbstractThe Bredt olefins bicyclo [3.3.1]non‐1‐ene (2), bicyclo [4.2.1]non‐1 (8)‐ene (3), and bicyclo [4.2.1]non‐1 (2)‐ene (4) react rapidly with 1,3‐dipoles such as diazomethane, phenyl azide, and mesitonitrile oxide to yield mixtures of two regioisomeric cycloadducts 10, 11 and 12, respectively. On the contrary, cycloaddition to the comparable monocyclic 1‐methyl‐(E)‐cyclooctene (5) is fairly regioselective. 2‐Methylnorborn‐2‐ene (6) gives one isomer with mesitonitrile oxide (as do less strained olefins), but mixtures with diazomethane and phenyl azide. 1H‐NMR. and 13C‐NMR. spectra of the cycloadducts are reported. The results are discussed in the light of frontier molecular orbital theory.
Isomerisierung der Bis(triphenylphosphin)platin(0)‐Komplexe von Bicyclo[4.2.1]non‐1‐en und Bicyclo[4.2.1]non‐1(8)‐en
Authors: Stamm Erich , Becker Konrad B. , Engel Peter , Keese Reinhart 
Published: December 2004

Isomerization of the Bis(triphenylphosphine)platin(0) Complexes of Bicyclo[4.2.1]non‐1‐ene and Bicyclo[4.2.1]non‐1(8)‐eneIsomrisation of the Bredt‐Olefins 3 and 7 as the bis (triphenylphosphine)‐Pt(0) complexes 1 and 8, respectively, has been observed. The bridgehead‐olefin 3 as well as the bicyclic olefins 4, 5 and 6 have also been isomerized with catalytical amounts of (ethylene)bis(triphenylphosphine)platinum(0) (2).
Etude par spectrométrie de masse d'une série d'alcanediphtalimides‐α,ω
Authors: Blanc Pierre‐Alain , Gülaçar Fazil O. , Buchs Armand 
Published: December 2004

Mass spectrometric study of a series of alkane‐α,ω‐diphthalimidesAlkane‐α,ω‐diphthalimides with three to seven aliphatic C‐atoms were synthesized and their mass spectral behaviour investigated in detail with the aid of the deuteriated derivatives of hexane‐1,6‐diphthalimide. Besides the expected hydrogen rearrangements, an interesting skeletal rearrangement has been observed.
Chirale 2,2′‐Polyoxaalkano‐9,9′‐spirobifluorene
Authors: Prelog Vladimir , Bedeković Davor 
Published: December 2004

Chiral 2,2′‐polyoxaalkano‐9,9′‐spirobifluorenesFrom 2,2′‐diacetyl‐9,9′‐spirobifluorene (2), twelve chiral polyethers have been prepared as potential ion‐ and enantiomer‐selective ionophores. The absolute configuration of the polyethers 15–17, 19–22, and 25 has been determined by chemical correlation with vespirenes [11] [29], by circular dichroism, and by X‐ray analysis. The circular dichroism of 15–17, 19 and 21 depends on the size of the macrocycle and indicates that the fluorene chromophores of 19 and 21 with 13‐ and 16‐membered rings respectively deviate considerably from orthogonality.
Elektrochemische Untersuchungen über das enantiomerenselektive Verhalten von chiralen Ionophoren in flüssigen Membranen
Authors: Thoma André P. , Viviani‐Nauer Angelika , Schellenberg Kurt H. , Bedeković Davor , Pretsch Ernö , Prelog Vladimir , Simon Wilhelm 
Published: December 2004

Electrochemical Investigations of the Enantiomer Selectivity of Chiral Ionophores in Liquid MembranesThe enantiomer selectivity of a series of chiral neutral ionophores was investigated by electrochemical methods using ionophore‐solvent‐polymer membranes and chiral ammonium salts as substrates. The potentiometrically determined enantiomer selectivities are in good agreement with the results of electrodialytic transport studies.
Carbocyclen aus Monosacchariden. III. Zur Diastereoselektivität der Bildung von Cyclopentanderivaten. Umsetzungen in der Galactosereihe
Authors: Bernet Bruno , Vasella Andrea 
Published: December 2004

Carbocycles from monosaccharides. III. Concerning the diastereoselective formation of cyclopentane derivatives. Transformations in the galactose series.The diastereoselectivity of the intramolecular nitrone‐olefine cycloaddition of 1, 3 and 4 (Scheme 1), yielding only 2, 5 and 6 but none of the isomers 8, 9 and 10 is explained by assuming a kinetic control and postulating that the relative activation energies of the two relevant transition states in the cyclization of e.g. 1 can be estimated from the conformers A and B, the latter being destabilized by a synperiplanar arrangement of the nitrone function and the 2‐alkoxy‐group (Scheme 2). It is further postulated, that this destabilization is responsible for the formation of (2,3)‐trans configurated products. Since 2, 5 and 6 are presumably thermodynamically more stable than 8, 9 and 10, a case was investigated, where the cycloaddition can either give thermodynamically less stable (2,3)‐trans‐product such as 12 or a thermodynamically more stable (2,3)‐cis‐product such as 13. 12 and 13 could both be formed from the aldehyde 25 via the nitrone 11 (Schemes 3 and 5). Treatment of the galactoside 16 first with Zn in aqueous butanol (forming among other products 25 and its 2‐debenzyl‐oxy‐derivative) and then with N‐Methyldroxylamine yielded the isoxazolidines 12 (72%), 13 (2%) and 27 (7%) (Schemes 4 and 6). Similarily, the anomeric silylated galactosides 17 and 23 gave 29 (78% from 17, 77% from 23) and 27 (5% and 3%). Upon desilylation, 29 gave 32, which was converted into 12. The structure of the isoxazolidines was unambiguously deduced from their NMR. spectra and those of their derivatives 33 and 34. Compound 32 was further transformed into its deoxyderivative 36. The high diastereoselectivity of the cycloaddition restricts the number of diastereomeric, pentasubstituted cyclopentanes available by this method. However, cyclization of the 2‐Hydroxy‐aldehyde 37 (Scheme 8) gave the kinetically less favoured isomer 40 in a higher proportion, showing the differential influence of hydrogen‐bonds on the relevant activation energies. Thermolysis of 32 gave 40 (79%) and 41 (11%). The structure of 41 was deduced from its NMR. spectra and those of its derivatives 42 and 43. Thermolysis of 29 gave, after desilylation, 41 (42%), 40 (22%) and 32 (13%) and thermolysis of 6 lead to a 25 : 75 equilibrium with 44 (combined yield 90%). These transformations illustrate means leading to additional isomers and are in agreement with the proposed explanation of the diastereoselectivity in question.
Towards the Construction of a Complete Cyclic Water Decomposition System, Design and Operation of an Oxygen Producing Half Cell
Authors: Kalyanasundaram Kuppuswamy , Mićić Olga , Pramauro Edmondo , Grätzel Michael 
Published: December 2004

AbstractOxygen is generated when aqueous solution of iron (III) tris(2,2′‐bipyridyl), Fe(bipy), are brought in contact with catalytic amounts of powdered or colloidal RuO2. The oxygen yield depends strongly on the pH, reaching a maximum between pH 7 and 8 where it corresponds to the stoichiometry of the reaction:
equation image
The rate of the reaction is so fast that it occurs practically upon dissolution of Fe(bipy) in the aqueous phase. In acidic media (pH 4), no O2 evolution is observed. Instead, Fe(bipy) is converted to an intermediate which in the presence of RuO2 yields O2 upon neutralization.The pH profile of the O2 evolution occuring upon illumination of Ru(bipy) in the presence of the cobalt complex [Co(NH3)5Cl]2+ was also investigated.The surprisingly low energy losses (160 mV) in reaction (1) makes the construction of four quanta water splitting systems feasible.
High Pressure 17O‐FT‐NMR. Evidence for the Associative Nature of Substitution Reactions on Mn2+ in Water
Authors: Ducommun Yves , Newman Kenneth E. , Merbach André E. 
Published: December 2004

AbstractThe water exchange on [Mn(H2O)6](ClO4)2 in aqueous solution has been studied as a function of pressure (up to 250 MPa), measuring 17O‐FT‐NMR. linewidths of the free water resonance at 8.13 MHz. A pressure independent volume of activation, ΔV≠ = −6.2 ± 0.2 cm3 mol−1 is obtained, producing a clear evidence that, contrary to general belief, the mechanism for solvent exchange on Mn2+ is an associative interchange (Ia).
Sorellin und Hobartin, zwei neue Indolalkaloide aus Aristotelia peduncularis (LABILL.) HOOK. F. 173. Mitteilung über organische Naturstoffe
Authors: Kyburz Rolf , Schöpp Emanuel , Hesse Manfred , Bick I. Ralph C. 
Published: December 2004

Sorelline and Hobartine, Two New Indole Alkaloids from Aristotelia peduncularis (LABILL.) HOOK. F.From Aristotelia peduncularis (LABILL.) HOOK. F. two new indole alkaloids, sorelline (1) and hobartine (2), have been isolated. Their structures were elucidated on the basis of spectroscopic data (the formulae represent their relative configurations). The alkaloids 1 and 2 have closely related structures with a monosubstituted indole moiety and an unrearranged monoterpene unit in the aliphatic part.
Metal Complexes with Macrocyclic Ligands. XIV. Formation, dissociation and metal exchange with an N2S2‐macrocycle
Authors: Kallianou Chariklia S. , Kaden Thomas A. 
Published: December 2004

Abstract10, 10, 12‐Trimethyl‐3,4‐benzo‐1,6‐dithia‐9,13‐diazacyclopentadecen‐dihydrochloride (LH, 2) and its Ni2+ complex were synthesized and their reactivity studied. The formation kinetics of 2 with Cu2+ were found to be a second order reaction between Cu2+ or CuACO+ and the monoprotonated form of the ligand LH+. The rate constant k = 29 M−1S−1 is 105–106 times smaller than those of monoprotonated tetraazamacrocycles either because of second bond formation or because of a strong electrostatic interaction between the positive charges of the Cu2+ and the ammonium group. The metal‐metal exchange between NiL+ and Cu2+ was also investigated. The reaction is independent of [Cu2+] and has the same rate and activation parameters as the dissociation of NiL2+. In contrast to open chain ligands, no mixed complex CuNiL4+ as intermediate was observed.
Über Pterinchemie. 72. Mitteilung. Trennung der Diastereomeren (6R)‐ und (6S)‐5,6,7,8‐Tetrahydro‐L‐biopterin
Authors: Furrer Hans‐Jürg , Bieri Jost H. , Viscontini Max 
Published: December 2004

Separation of the Diastereomers (6R)‐ and (6S)‐5,6,7,8‐Tetrahydro‐L‐biopterinThe mixture of the diastereomers of the tetraacetylderivative IV of (6RS)‐5,6,7,8‐tetrahydro‐L‐biopterin could be separated by fractional crystallisation in methanol into the diastereomers IV A and IV B. Hydrolysis with hydrochloric acid gives the pure, diastereomeric, (6R)‐ and (6S)‐5,6,7,8‐tetrahydro‐L‐biopterins.
2‐Oxocephems. Synthesis and Properties of 7‐Acylamino‐2‐oxocephem‐4‐carboxylic Acids
Authors: Ernest Ivan 
Published: December 2004

AbstractA synthesis of (6 R, 7 R)‐7‐acylamino‐2‐oxocephem‐4‐carboxylic acids from penicillins is reported based on the formation of the 2‐oxocephem system in an intramolecular Wittig condensation. An interesting steric effect of the acylamino grouping on the course of this key step was used to advantage. Some physical and biological properties of this new type of Δ3‐cephem are described.
Iridoidglucoside aus Leucocarpus perfoliatus G. DON. 174. Mitteilung über organische Naturstoffe
Authors: Ozaki Yutaka , Hesse Manfred , Johne Siegfried 
Published: December 2004

Iridoidglucosides from Leucocarpus perfoliatus G. DON.The known iridoid glucoside boschnalosid (1) was isolated from Leucocarpus perfoliatus in addition to the hitherto unknown yuheinosid, for which structure 2 was deduced.
The Course of the Catalytic Hydrogenation/Isomerization Reaction of Steroidal Ring B Olefins in the 13β‐ and 13α‐Series
Authors: Acklin Georg , Graf Walter 
Published: December 2004

AbstractThe course of the catalytic hydrogenation and isomerization (H2/Raney‐Ni/dioxane or H2/Pd/C/EtOH) of Δ5.7‐, Δ7‐, Δ8‐, and Δ8(14)‐steroid olefins was shown to depend strongly on the configuration at C(13). The known hydrogenation/isomerization of reactions of Δ5.7‐dienes in the 13β‐series to Δ7‐(H2/Raney‐Ni/dioxane) and Δ8(14)‐olefins (H2/Pd/C/EtOH) were also confirmed in the 3β, 19‐epoxy‐13β‐ and 3‐Oxo‐19‐acetoxy‐13β‐steroid series (e.g. 32 → 35 → 37, Scheme 3). On the other hand, in the corresponding 13α‐steroid series the same reactions afforded the Δ7‐. and the Δ8‐olefins (mixture of products with H2/Raney‐Ni/dioxane; quantitatively the Δ8‐compounds with H2/Pd/C/EtOH; s. e.g. Scheme 3). A similar dependence on the C(13) configuration was observed in the allylic oxidation of these olefins with SeO2 (Fieser's test, see Table), and in the acid catalyzed opening of the 7α, 8α‐epoxides (e.g. 60 → 62 + 63 in the 13β‐series, and 56 → 64 + 65 in the 13α‐series, Scheme 8).
The photoelectron spectra of D2d and C2ν hydrocarbons containing two norbornadiene or quadricylane groups
Authors: Kovač Branka , Heilbronner Edgar , Prinzbach Horst , Weidmann Klaus 
Published: December 2004

AbstractThe photoelectron spectra of the hydrocarbons 1 to 4 have been recorded and interpreted by qualitative correlation with the spectra of their subsystems norbornadiene, quadricyclane, allene and cyclopropane.It has been shown that the interactions of the symmetry adapted orbitals of the subsystems are governed not only by their symmetry behaviour with respect to D2d in 1 and 2, or C2ν in 3 and 4, but also by the local symmetry at the points of attachment of the subsystems.
Synthese von (‐)‐(R)‐4‐Hydroxy‐β‐ionon und (‐)‐(5 R, 6 S)‐5‐Hydroxy‐4,5‐dihydro‐α‐ionon aus (‐)‐(S)‐α‐Ionon
Authors: Haag Andreas , Eschenmoser Walter , Eugster Conrad Hans 
Published: December 2004

Synthesis of (‐)‐(R)‐4‐Hydroxy‐β‐ionone and (‐)‐(5 R, 6 S)‐5‐Hydroxy‐4,5‐dihydro‐α‐ionone aus (‐)‐(S)‐α‐IononeThe absolute configuration of the chiral 4‐hydroxy‐β‐ionones and 5‐hydroxy‐4,5‐dihydro‐α‐ionones has been determined by chemical connection with (‐)‐(S)‐α‐ionone i.e. by stereoselective epoxidation of the latter, followed by base catalyzed opening of the epoxide as well as by its hydride reduction.
A Reexamination of Inductive Substituent Constants Derived from pKa Values of 4‐Substituted Quinuclidines. Polar effects. Part VIII
Authors: Grob Cyril A. , Schaub Bruno , Schlageter Markus G. 
Published: December 2004

AbstractpKa Values of 42 quinuclidinium perchlorates I have been measured in 0.1 M aqueous KCl‐solution. In a few cases small corrections of earlier thermodynamic pKa values are indicated. These measurements, in conjunction with recent X‐ray structure determinations, confirm the reliability of the inductive substituent constants σIq derived from them.
Approaches to the Synthesis of Cytochalasans. Part 2. Pyrrolinone derivatives as basic units
Authors: Schmidlin Tibur , Tamm Christoph 
Published: December 2004

AbstractSeveral attempts to prepare 3‐acetyl‐5‐benzyl‐3‐pyrrolin‐2‐one (7) from phenylalanine are described. This goal was only reached formally, because compound 7 exists in the tautomeric form of (Z)‐5‐benzyl‐3‐(1′‐hydroxyethylidene)‐4‐pyrrolin‐2‐one (17) according to the spectral data. The problem of tautomerism in pyrrolinone systems is discussed.
Valence Delocalization in Prussian Blue Fe[FeII(CN)6]3 · XD2O, by Polarized Neutron Diffraction
Authors: Day Peter , Herren Fritz , Ludi Andreas , Güdel Hans Ulrich , Hulliger Fritz , Givord Dominique 
Published: December 2004

AbstractPolarized neutron diffraction has been used to investigate the spin delocalization from the high‐spin Fe(III) sites to the low‐spin Fe(II) in deuteriated Prussian Blue, Fe4[Fe(CN)6]3 · xD2O. Measurements of the 111, 200, and 400 reflections were made on a powdered sample at 3 K and 4.8 T using a neutron wavelength of 1.074 Å. The expectation value of S at the Fe(II) site is ‐ 0.008 ± 0.028 corresponding to an upper limit of about 5% of an electron for the spin delocalization.
Photochemische Reaktionen. 106. Mitteilung. Zur Photochemie tetraalkylsubstituierter γ‐Keto‐olefine
Authors: Berger Jacob , Yoshioka Michikazu , Zink Markus P. , Wolf Hans R. , Jeger Oskar 
Published: December 2004

The Photochemistry of Tetraalkyl Substituted γ‐Keto‐olefinesThe photochemistry of 7,8‐dihydro‐β‐ionone (1) in solution is shown to depend on temperature, polarity and viscosity of the solvent. UV. irradiation (λ ≥ 245 nm) in pentane at +25° converts 1 to the isomeric ethers 3 (16%), 5A (48%) and 5B (22%), whereas at −65° 7,8‐dihydro‐γ‐ionone (26) is obtained in 12% yield together with 13% of 3, 12% of 5A and 9% of 5B. The 1n,π*‐excitation of 1 in acetonitrile gives similar results. In the more viscous 1,2,3‐triacetoxypropane the photoisomerization 1 → 26 takes place even at + 60° (10% yield, cf. 40% at −15°). In alcoholic solvents, however, no formation of 26 is detected, but the hitherto unknown [2+2]‐photocycloaddition 1 → 11 can be observed (4% at −7°, 15% at −65S° in 2‐propanol). An intermediate e may be involved (Scheme 14). In addition to the photoreactions 1 → 3, 5A, 5B and 11 the isomerization of 1 to the novel spirocyclic ketone 28 takes place in alcoholic solvents only.Photoisomerization 1 → 3 is presumably a photo‐ene process involving a stereoselective intramolecular H‐transfer. This type of photoisomerization is restricted to cyclic γ‐keto‐olefines. The tetraalkylated acyclic γ‐keto‐olefines 14 and 15 photoisomerize exclusively by [2+2]‐cycloaddition, independent of the solvent.On 1n,π*‐excitation the δ,ϵ‐unsaturated bicyclic ketone 44 undergoes Norrish‐Type‐II photofragmentation to the diene 45 or isomerizes to the γ, ϵ‐unsaturated ketone 17. Competition between these two reactions is strongly temperature dependent: photolysis in pentane at −72° yields quantitatively 45, whereas at + 35° only 30% of 45 and 68% of 17 are obtained.UV. irradiation of the novel spirocyclic ketone 28 gives as primary photoproduct the isomeric aldehyde 29, and in a secondary photoreaction the isomeric oxetanes 30A and 30B. Experiments with deuteriated substrates show that the isomerization of type 28 → 29 is stereocontrolled.
Revision of the Structure of ‘Epoxycolchicine’
Authors: Brossi Arnold , Rösner Manfred , Silverton James V. , Iorio Maria A. , Hufford Charles D. 
Published: December 2004

Revision der Struktur von «Epoxycolchicin»Die für natürliches «Epoxycolchicin» vorgeschlagene Struktur 2 muss aufgrund einer Kristall‐Röntgenstrukturanalyse zu derjenigen des cyclischen Acetals 3 abgeändert werden. Es wird vorgeschlagen, den Namen «Epoxycolchicin» aus der Literatur zu streichen, da er irreführend ist.
Light Induced Redox Reactions of Water Soluble Porphyrins, sensitization of hydrogen generation from water by zincporphyrin derivatives
Authors: Kalyanasundaram Kuppuswamy , Grätzel Michael 
Published: December 2004

AbstractThe photoredox behaviour of two water soluble derivatives of zincporphyrin, 5,10,15,20‐tetra‐p‐sulfonatophenyl (1) and 5,10,15,20‐tetra‐p‐N‐methylpyridiniochloride (2), was investigated using laser and continuous photolysis techniques. Photoexcitation produces triplet states whose lifetimes in aqueous solution exceeds 1 ms. These triplet states can be quenched reductively by donors such as EDTA and oxidatively by acceptors such as methylviologen (MV2+). Electron transfer to MV2+ is greatly influenced by the charge of the porphyrin, rate constants being 1.4 x 1010M−1S−1 and 2 × 106M−1S−1 for 1 and 2, respectively. In the presence of colloidal Pt catalyst, the cationic porphyrin sensitizes photoreduction of water to hydrogen with remarkable efficiency.
Oxygen‐17 and Carbon‐13 Nuclear Magnetic Resonance. Chemical shifts of unsaturated carbonyl compounds and acyl derivatives
Authors: Delseth Claude , Nguyên Thi Thanh‐tâm , Kintzinger Jean‐Pierre 
Published: December 2004

AbstractThe 17O and 13C chemical shifts (δ) of 14 α,β‐unsaturated aldehydes and ketones and 33 acyl derivatives RXC = O (X = Cl, OH, OMe, OEt, NH2 and R = H or alkyl) have been measured. In the unsaturated carbonyl series, a correlation exists between δ 17O and the π electron density at the β‐carbon atom. From this correlation, an δ 17O of 530 ppm was extrapolated for the loss of one electron at the oxygen atom. In the acyl series, the δr 17O were also sensitive to changes in the polarity of the carbon‐oxygen bond. A partial correlation between 17O‐NMR. chemical shifts and the nuclear quadrupole coupling constants exists for aldehydes, ketones, esters and amides but not for acyl chlorides.