Showing papers by "University of Fribourg published in 1975"

Kinetik und stereochemischer Verlauf der thermischen Umlagerung der vier stereoisomeren Propenyl‐(but‐2′‐enyl)‐äther

Abstract: The gas-phase rearrangement of (1Z, 2′E)-, (1Z, 2′Z)-, (1E, 2′E)-, and (1E, 2′Z)- propenyl but-2′-enyl ether (Z, E)-, (Z, Z)-, (E, E)-, and (E, Z)-1) into erythro- and threo-2, 3-dimethyl-pent-4-en-al (erythro- and threo-2) was investigated over a temperature range from 142,5° to 190,0° at 20–35 Torr (for kinetic data and activation parameters see table 2). All four stereoisomeric ethers 1 rearrange preferentially via a chair-like transition state C into the aldehydes 2 (ΔΔG≠ (160°) = 2,5–2,7 kcal/mol for B – C (B = boat-like transition state). The relative rates (krel) for (Z, Z)-1, (Z, E)-1, (E,Z)-1, and (E,E)-1 at 160° are 1,0, 2,9, 4,3 and 9,0 respectively (see table 5). Taking into account the relative enthalpies of the ethers 1 and the steric interaction in the C transition state of the ethers 1 (see table 6), krel values can be estimated. They are in good agreement with those observed (see table 5).

Photoinduzierte Reaktionen von 3‐Phenyl‐2H‐azirinen mit Carbonsäureestern 40. Mitteilung über Photoreaktionen

Abstract: Irradiation (280–350 nm light) of a benzene solution of 3-phenyl-2H-azirines 1a–e in the presence of carboxylate esters, whose carbonyl groups are activated by electron withdrawing groups situated in the acyl or alkyl moiety, produces 5-alkoxy-3-oxazolines (Tab. 1 and 4, Scheme 2) isolated in 18–82% yield. These heterocycles undoubtedly originate by regiospecific addition of the ester carbonyl group to the azirine-derived benzonitrile-methylide ‘dipole’ (Scheme 1). The 5-(2,′ 2′, 2′-trifluoroethoxy)-3-oxazolines, derived from 2′, 2′, 2′-trifluoroethyl carboxylic esters, on treatment with methanolic hydrogen chloride at low concentration, are smoothly transformed into the corresponding 5-methoxy-3-oxazolines (e.g. 16 17, Tab. 5). Utilizing this process, various hitherto relatively unknown 9. 5-alkoxy-3-oxazolines become accessible. The constitution of the adducts is based essentially on spectral data. The structure of trans-5-methoxy-2,4-diphenyl-5-trifluoromethyl-3-oxazoline (trans-14), the addition product of methyl trifluoroacetate and the benzonitrile-benzylide from 2,3-diphenyl-2H-azirine (1d), was determined by X-ray crystallography (Section 5). Benzonitrile-isopropylide (22), resulting from the photochemical transformation of 2,2-dimethyl-3-phenyl-2H-azirine (1a), also reacts with S-methyl thiobenzoate to give 2,2-dimethyl-5-methylthio-4,5-diphenyl-3-oxazoline (26). Ethyl cyanoacetate protonates predominantly the dipolar species derived from 1a at the nitrile C-atom and yields after work-up ethyl α-cyano-cinnamate (29) and ethyl isopropylidene-cyanoacetate (30) (Scheme 4). The relative rate of addition (krel) of benzonitrile-isopropylide (22) to methyl α-haloacetates and dimethyl oxalate was determined by competition experiments (Section 6). Log krel correlated satisfactorily (r = 0.97) with the pKa of the acide derived from the ester reactant: log krel = − 1.72 pKa + 2.58 or with Taft's substituent constants σ*: log krel = 2.06 σ* − 4.11 [krel(methyl dichloroacetate) = 1; Section 7.1]. On the basis of the results obtained, the mode of reaction of the so-called benzonitrile-methylide ‘dipole’ is discussed and a model for the transition state of addition of ester-carbonyl groups is proposed that accounts for the observed regiospecifity and steroselectivity.

Photochemical Cyclization of Allylated Anisole and N-Alkyl Aniline Derivatives. Preliminary communication†

Abstract: The allyl anisole derivatives 1, d2-1, 3, 5 and 7 (Scheme 1), on exposure to UV. light in benzene, acetone or methanol solution, cyclize to yield the corresponding cyclopropyl anisole derivatives 2, d2-2, cis- and trans-4, 6 and 8, respectively. Under the above conditions the N, N-dialkyl-2-allyl anilines 9, 10 and 11 give similar results (Scheme 2). On the other hand, N-alkyl-2-allyl anilines (15 and 19, Scheme 3) are transformed by UV. light in cyclohexane or benzene solution into 2-methyl-indolines (16 and 20, resp.), whereas in methanol solution the corresponding 2′-methoxy compounds 18 and 21 are formed in addition to 16 and 20, respectively.

The Phenomenological Reduction as Epoche and as Explication

Abstract: A clear understanding of the notion of phenomenological reduction is crucial for any evaluation of the claims of Husserlian phenomenology. The phenomenological reduction is said to be the distinctive step (or steps) one has to take if one is to enter the realm of phenomenology proper. Husserl labored all his life to find the best way which would lead the nonphenomenologist into the new land which he thought he had discovered. Commentators have classified the ways discussed by Husserl under at least three main headings: the Cartesian way, the way through psychology, and the way through ontology. In each of these ways, one is urged to perform a phenomenological reduction. But since the ways are different, the step also of the phenomenological reduction varies somewhat for each approach. Husserl and his interpreters tried hard to clarify these subtle distinctions, but up to now their ways of speaking have proven rather opaque, especially to philosophers accustomed to the standards of clarity of Analytic Philosophy.

Säurekatalysierte Umlagerung von 4‐Allyl‐cyclohex‐2‐en‐1‐olen; Beispiele für ladungskontrollierte [3s, 4s]‐Umlagerungen von cyclischen Allylkationen

Abstract: The acid-catalysed rearrangement of the cyclohex-2-en-1-ols 15, d3-15, 16, 17 and 19, the cyclohexa-2,5-dien-1-ols 20 and 21, and also the allyl alcohols 22 and 23 (Scheme 3), using 98-percent sulfuric acid/acetic anhydride 1:99 at room temperature, was investigated. From the rearrangement of 4-allyl-4-phenyl-cyclohex-2-en-1-ol (15), with reaction times greater than 2 hours a single product is obtained, 4-allyl-biphenyl (50) in 33% yield (Scheme 9). With reaction times below 2 hours the acetate 53 from 15 was isolated, and this could be converted into 50. The reaction of 2′,3′,3′-d3-15 in Ac2O/H2SO4 lead to 1′,1′,2′-d3-50 (Scheme 11). The rearrangement of 4-allyl-4-methyl-cyclohex-2-en-1-ol (16) (Scheme 14) yielded 39% of the corresponding acetate 60 and 30% of 4-allyl-toluene (6), which also resulted by a rearrangement of 60 under the reaction conditions. These rearrangements are all [3s,4s]-sigmatropic reactions, which proceed via the cyclohexenyl cation a (Scheme 12, R = C6H5, CH3). In Ac2O/H2SO4 the allyl-cyclohexadienes primarely formed subsequently undergo dehydrogenation to yield the benzene derivatives 6, 50 and d3-50. From the rearrangement of 4,4-diphenyl-cyclohex-2-en-1-ol (19) at 0° a reaction mixture is obtained which consists of the acetate 55, 2,3-diphenyl-cyclohexa-1,4-diene (57) and o-terphenyl (56) (Scheme 10). Both 55 and 57 are converted under the reaction conditions to o-terphenyl (56). No 4-(1′-methylallyl)-biphenyl is obtained from the rearrangement of 4-crotyl-4-phenyl-cyclohex-2-en-1-ol (17). In this case, apart from the corresponding acetate 64, a single product 5-(1′-acetoxyethyl)-1-phenyl-bicyclo[2.2.2]oct-2-ene (65) (Scheme 16) was obtained; under the reaction conditions the acetate 64 rearranges to 65. The rearrangement of 4-allyl-4-phenyl-cyclohexa-2,5-dien-1-ol (20) gives, as expected, not only 4-allyl-biphenyl (50) but also 2- and 3-allyl-biphenyl (51 and 52) and biphenyl (Scheme 13). 4-Benzyl-4-methyl-cyclohexa-2,5-dien-1-ol (syn- and anti-21) gave in Ac2O/H2SO4 at 10° as rearrangement products 93% of 2-benzyltoluene (97) and 7% of 4-benzyl-toluene (98) (Scheme 21). Hence [1,4]-rearrangements in cyclohexadienyl cations, seems to occur only to a limited extent. The alicyclic alcohols 22 and 23 (Scheme 18) gave, in Ac2O/H2SO4, as main product the corresponding acetates 73 and 75, as well as small amounts of olefins 74 and 76 formed by dehydration i.e. [3,4]-rearrangements occur in these systems. Also no [3,4]-rearrangements were observed in solvents reactions of either 4,4-dimethyl-hepta-1, 6-dien-3-yl tosulate (79; see Scheme 19) or its corresponding alcohol 24.

On re-normalization in the theory of weak turbulence in plasmas

Abstract: The paper compares the methods of re-normalization introduced by the Dupree—Weinstock theory of turbulence with those in the theories of Kadomtsev, Rudakov and Tsytovich. It is shown to what extent they are equivalent.

Zur Konstruktion komplexer Basen

Abstract: A method of Stein [17] is generalized to construct in an explicit way complex bases of open holomorphic mappings, defined on normal complex analytic spaces. Using theorems concerning the existence of pushouts, we can sharpen a theorem of Wolffhardt ([22],§4) and generalize the above construction. As a consequence, we can prove for a big class of complex bases b:X→B, that the induced mapping π1(X)→π1(B) its surjective. We give a characterisation of locally simple and analytically locally simple analytic equivalence relations.

Fluorénacènes et fluorénaphènes Synthèses dans la série des indéno‐fluorènes, XIX Dérivés tétraméthylés du trans‐fluorénaphène et du trans‐fluorénacène

Abstract: By condensation of isophthaloyldichloride resp. of terephthaloyldichloride with 4-bromo-1,2-xylene according Friedel-Crafts, followed in each case by a double cyclisation and a final reduction, the 2,3,9,10-tetramethyl-7,12-dihydro-indeno[1,2-a]fluorene resp. the 2,3,8,9-tetramethyl-6, 12-dihydro-indeno[1,2-b]fluorene are synthesized.

Sur les dérivés de la fluorénone VIII. Difluorénonyl‐cétones, difluorényl‐cétones et difluorényl‐méthanes

Abstract: By condensation of the chlorides of the four isomeric fluorenecarboxylic acids, respectively of the three 1-, 3- and 4-fluorenonecarboxylic acids with fluorene, followed by reduction of the obtained mono-respectively diketones, the four difluorenylmethanes I, II, III and IV are synthesized. The oxydation of the diketones gives the corresponding triketones. Starting from the chloride of 4-fluorenecarboxylic acid and 1-methylfluorene, a methyl derivative of IV is analogically obtained.

Contribution à l'étude de la mésomérie, X Simplification du calcul des éléments du déterminant séculaire par voie graphique Système formé d'un atome à quatre électrons et de n atomes à un électron chacun

Abstract: On indique une methode graphique simplifiant considerablement, dans le cadre de la methode de mesomerie, le calcul des elements du determinant seculaire et par consequent celui de l'energie et de la repartition electronique. Les regles de calcul presentees sont valables pour un systeme forme d'un atome a quatre electrons et d'un nombre quelconque d'atomes a un electron chacun. En outre, il a ete possible de reunir dans un seul ensemble les regles valables pour des systemes d'un atome a 1, 2, 3 ou 4 electrons et de n atomes a un electron chacun.

A model relating transfer of learning and correlation

Abstract: The theoretical and practical importance of a double undertaking is discussed: the development of learning and transfer taxonomies with psychometric relevance and the building of psychometric classificatory systems with implications for learning and instruction. Psychometric classifications of human performances are most often based on the covariation of individual differences. The model presented justifies the expectation that the transfer from learning one task to learning another is linearly dependent on the coefficient of intercorrelation between the two tasks when the coefficient is corrected for attenuation. Two studies so far have explicitly confirmed the main deductions from this model. Contrary to the predictions, however, the regression curves yielded negative intercepts. Two empirically testable explanations are offered, one of which would be in full accordance with the model, while the other would call for a further assumption.

On the diffraction of electromagnetic waves by semi-infinite bodies of revolution

Abstract: The radiation characteristics for nearly-conical, semi-infinite, perfectly conducting bodies of revolution are calculated. The excitation is assumed to be performed by the given currents distributed in an axial-symmetric way at the top of the body and the wave-length of radiation emitted is assumed to exceed the radius of curvature of the top greatly. The problem of radiation from the top of conducting hyperboloid is solved exactly. For similar cases, not allowing the separation of variables, an approximate method based on separation of fields in quasi-static (corresponding to the proximity of the top) and wave-zones is formulated. It is shown that the total radiation loss for such nearly-conical bodies of revolution depends upon the frequency ω of the given currents as ωn. The powern is smaller than the valuen=4 corresponding to the Hertz's dipole and is determined uniquely by the cone's vertical angle.