Showing papers by "University of Fribourg published in 1978"

Zum photochemischen Verhalten von Sydnonen und 1,3,4‐Oxadiazolin‐2‐onen. 56. Mitteilung über Photoreaktionen

Abstract: The photochemical behaviour of several 3,4-disubstituted sydnones (cf. Scheme 5) in dioxane solution was investigated. The pure sydnones give, as was already reported [2-6], 2,4,5-trisubstituted 1,2,3-triazoles 2 (cf. Scheme 1) in 25-30% yield. In the presence of dipolarophiles (cf. Scheme 1) pyrazole derivatives 3 or 4 are formed which can be taken as a proof for the formation of nitril-imines 5 as primary products in sydnone photochemistry. Since irradiation of 2-[15N]-3,4-diphenyl- sydnone (2-[15N]-15) in dioxane leads to the formation of 1,3-[15N]-2,4,5-triphenyl-1,2,3-triazole (1,3-[15N]-22; cf. Scheme 10), nitril-imine formation must be induced by the creation of a bond between N(2) und C(4) in the excited sydnones (cf. Scheme 22). The irradiation of sydnones in dioxane solution in the presence of carboxylic acids yields N'-acylhydrazides in 50-70% (cf. Scheme 14), the formation of which can be explained by addition of the acids to the nitril-imines and rearrangement of the primarily formed anhydride monohydrazones (Scheme 15). By analogy, the formation of 1-benzoyl-2-(t-butyl)-4-phenyl-1,2-diazetidin-3-one (14; Scheme 4 ) during the photolysis of 3-(t-butyl)-4-phenylsydnone (12) in benzene solution (cf. [5b]) may also be explained: Sydnone 12 undergoes two different photoreactions leading by loss of carbon dioxide to the corresponding nitril-imine 5 (R = t-C4H9, R' = C6H5) and by loss of isobutylene to a 1,2,3-oxadiazolin-5-one of type 48 or 49 which isomerizes to yield diazophenylacetic acid (51; cf. Scheme 17). Reaction of both products (5 and 51) results in the formation of the N'-acylhydrazide 52 (Scheme 18) which may cyclize after loss of nitrogen to yield the diazeti- dinone 14 in a carbene type reaction. The triazoles 2 are formed photochemically from the corresponding 1,2-bisazo-ethylenes 64 (Scheme 26) which arise from a direct 'head-to-head' dimerization of the nitril-imines 5. This type of reaction seems to be common to all nitrilium betaines (Schema 30). The photolysis of the 2,4-disubstituted 1,3,4-oxadiazolines 76 does not lead to nitril-imines 5 (cf. [11]). On the contrary, loss of carbon monoxide induces the formation of azoketones 77 (cf. Scheme 31), which may be photo-reduced to yield hydrazides or may undergo cleavage of the N,acyl bond to form derivatives of 1,2-diketones (cf. Scheme 32).

Zur Photochemie von Allylaryläthern. 55. Mitteilung über Photoreaktionen

Abstract: The photochemical reactions of different allyl aryl ethers (Scheme 3) were investigated in hydrocarbons (Chap. 3.1) and in alcoholic solvents (Chap. 3.2). The composition of the photoproducts depended very much on the nature of the solvent. Irradiation (3-95 h) of different methyl substituted allyl aryl ethers (1, 3, 5, 7 and 11) with a low pressure mercury lamp (lambda(Emiss.) = 254nm; 6 or 15 Watt) under argon (quartz vessel) resulted in the formation of 2-, 3- and 4-substituted phenols, dienones and products of consecutive reactions (Tables 1-4 and 6). The results suggested that all products were formed by homolytic cleavage of the C-O bond in the singlet state of the ethers to intermediate radical-geminates (Scheme 5) followed by radical recombination of the two fragments. No products were formed by concerted processes (Table 5, Schemes 5 and 6). Upon irradiation of allyl aryl ethers lacking alkyl substituents at position 4 (1 and 5) in protic solvents, mainly 2- and 4-allylated phenols were obtained (Tables 1 and 4); 3-allylated phenols were formed only in small amounts (0.02%). However, in aromatic hydrocarbons or cyclohexane 3-allylated phenols were obtained from 1, 5 and 11 in significant amounts (3-11%; Tables 1, 4 and 6). E.g., upon irradiation of allyl-2,6-dimethylphenyl ether (5) in toluene, the main photoproduct was 6-allyl-2,6-dimethy1-2,4-cyclohexadien-1-one (6) besides 3- and 4-ally1-2,6-dimethylphenol (23 and 24). Irradiation of 5 in methanol afforded 23 and 6 only in traces, whereas 24 was the main product. Ethers alkylated at position 4 (3 and 7) yielded 3-allylated phenols after irradiation in hydrocarbons and in methanol (Tables 2 and 3). The time independent equilibration of deuterium labelling in the allyl chain of dienone d3-6 obtained upon irradiation of 2,6-dimethylphenyl-2’, 3’, 3’-trideuterioallyl ether (2’,3’, 3’-d3-5) (cf. Table 5) demonstrated that the photolysis of aromatic allyl ethers did not occur by a [1s,3s]-sigmatropic process (cf. Chap. 3.1.4.2). For the photochemical formation of 3-allylated phenols, the following two mechanisms may be envisaged: 1. According to CIDNP measurements [12] at least one portion of the 3-allylated phenols 14, 20 and 23 is produced via a direct recombination of the triplet-geminate, which is formed from the singlet-radical-geminate via intersystem crossing (Scheme 5, pathway d). 2. Formation of 4-allyl-2,5-cyclohexadien-1-ones (III, IV and 12) could occur via a singlet-geminate (Scheme 5, pathway c). These dienones undergo photochemical excitation and give bicyclic intermediates, which after further photoexcitation are finally transformed into the 3- allylated phenols 14, 20 and 23 (cf. Scheme 6, pathway g, h and i). This path allows the formation of significant amounts of 3-allylated phenols (3- 11%) during photo-Claisen-rearrangement of allyl phenyl ethers lacking a substituent at position 4. The lifetimes of the initially formed 4-monosubstituted dienones III and IV in hydrocarbons were long enough to permit photochemical isomerization to 3- allylated phenols. In protic solvents however, a fast enolization of 3 and IV to 4-allylated phenols is expected, so that the photochemical isomerization is interrupted. The presence of bases which catalyse this heterolytic enolization further suppress the photochemical isomerization (Table 1). The very small amount (0,01- 0,1%) of 3-allylphenols, which were still formed after the irradiation of allyl aryl ethers lacking a substituent at position 4 in protic solvents or under basic conditions, must be produced by direct radical recombination within the triplet-geminate (cf. Scheme 5, pathway m and n). Free phenoxy and allyl radicals were also formed from the triplet-geminate (cf. ESR. experiments, Chap. 5). The former yielded the observed phenols after hydrogen abstraction from the solvent. A crossover experiment with tritiated ether 3’-t-3 and ether 1 suggested that recombination of free phenoxy and allyl radicals during photolysis did occur only to a very small extent (2 - 0,1%; cf. Chap. 4). The photochemical transformation of ((E)- or (Z)-2’-buteny1-2,6-dimethylphenylether ((E)- and (Z)-11, respectively) to (E)- or (Z)-6-(2’-butenyl)-2,6-dimethyl-2,4-cyclohexadien-1-one ((E)- and (Z)-26, respectively) at 7° showed, that the configurational integrity of the allyl radical was maintained (90-95%) until the recombination had occurred (Table 6).

Spinal projection to the dorsolateral nucleus of the caudal basilar pons in the cat.

Abstract: In the cat, a spinal projection to a restricted area of the basilar pontine grey has been revealed with use of anterograde degeneration technique (Fink-Heimer). The area was ipsilateral to the spinal lesion, restricted to the far caudal limit of the pons, and included the dorsal and the dorsolateral subdivisions of the pontine nuclei (PN). Comparisons following high cervical, midthoracic and upper lumbar spinal lesions did not reveal any somatotopic organization. Only a few spinopontine fibers had origins below segmental level L4. Lesions of various quadrants of the cord indicated that the spinopontine fibers ascended through the dorsolateral funiculus, and not through either the dorsal or the ventral funiculi. Comparison with the degeneration effects of cerebral cortical lesions showed that the spinal projection to the PN overlapped to some extent with the projection from the first sensorimotor and second somatosensory cortices. In the rat no comparable spinopontine projection was found. It is suggested that the spinopontine pathway might forward information to the cerebellum from visceral sensory receptors or perhaps from pools of spinal interneurons.

Electromyographic assessment of central motor disorders.

Abstract: Experimental procedures are described that were designed to assess central motor disorders quantitatively. Initially delineated is a study of triggered ballistic movement performed in a reaction-time situation. The reciprocal triphasic EMG pattern recorded in an antagonistic muscle pair was clearly abnormal in Parkinsonian patients; increased duration, diminished synchronization of motor units, and a tendency for coactivation of agonist and antagonist muscles and for action tremor were observed. Transport time of elbow movement was prolonged, particularly in a choice reaction-time situation. Rapid, passive displacements of the forearm combined with excitability measurements of hindlimb motoneurons in monkeys revealed the existence of a transcortical loop that may contribute to increased muscle tone in Parkinsonian patients.

Untersuchungen über Allylgruppenwanderungen in aliphatischen Carbenium‐Ionen

Abstract: Investigations on the Migratory Aptitude of Allyl Groups in Aliphatic Carbenium-Ions The acetolysis (80°) of the 4-bromobenzenesulfonates given in Scheme 6 were investigated in regard to determine type allyl/methyl migratory aptitudes in the secondary carbenium ion a (Scheme 24). In all cases olefins (about 80%) and acetates (about 20%) were formed which can be derived from the rearranged tertiary carbenium ions b (being formed by allyl group migration) and c (being formed by methyl group migration). Olefin A and acetate H, originated in carbenium ion a, occurred in the acetolysis mixture only in minor amounts (<2%). By acetolysis of [l4C]-20, isolation of [14C]-4,5-dimethyl-l, 3-hexadiene ([14C]-45), and degradation of this diene (Scheme 16) it could be shown (4 Scheme 15) that the ions b and c (Scheme 24, R1R4H) are not interconverted by a [1,2]-hydride shift (extent < 1%). Since olefin D arises by proton loss from ion b as well as from ion c, [14C]-4,5-dimethyl-l,4-hexadiene ([14C]44 D, R1R4 H) was also degraded (cf. Scheme 15 and Scheme 17). It was found that [14C]-44 contained 48% of the label in the methyl group at C(4) and 52% in the methyl groups at C(5), i.e. 48% of 44 is formed via the allyl migration path and 52% via the methyl migration path. In addition, acetolysis of d3-20 and product analysis showed, that the d3-ally1 moiety migrates as expected only in a [1,2]-fashion. Product analysis of the acetolysis mixtures of erythro- and threo-24 (cf. Scheme 19 and Tables 4 and 5) revealed that carbenium ion a must exist as an intimate ion pair (with the 4-bromobenzenesulfonyloxy-ion) which has lost its configuration at C(1) only partially. This is indicated by reversed ratios (1: 11 and 10: 1, resp.) in the formation of erythro- and threo-2,3,4-trimethyl-l, 5-hexadiene (erythro- and threo-77) arising from ion b (Scheme 24, R1R3 H, R4 CH,). The acetolysis of 1,2,2,4-tetramethyl-4-pentenyl4-bromobenzenesulfonate (23) was not studied in detail, but the appearance of a seventh product in the olefin part cannot be explained by the genesis paths in Scheme 24. Thus, it may be concluded that in this case a third tertiary carbenium ion d3 (Scheme 21) is produced by cyclization of a3. Cyclizations of this type are known to occur in carbenium ions bearing β-substituted allyl groups (see Scheme 22). The kinetic data of the acetolysis of all 4-bromobenzenesulfonates (Table 6) are in accord with a rate determining ionization step leading to a since all activation enthalpies resp. entropies are within 25.5 L± 0.6 kcal/mol resp. −0.2 ± 1.7 e.u. The migratory aptitudes given in Table 7 show, that allyl groups migrate only slightly easier than methyl groups in ion a. This is in strong contrast to allyl substituted methylcyclohexadienyl cations (generated in the acid catalyzed dienone/phenol and dienol/benzene rearrange-ment) which undergo exclusively [1,2]-ally1 migrations (Schemes 3-5).

Standing waves in a magnetized plasma cylinder of finite length

Abstract: The magnetic field component Bz generated in a magnetized plasma cylinder was measured at frequencies reaching from well below the first magnetoacoustic resonance up to the lower hybrid resonance. In this spectrum between 1 MHz and 100 MHz the first, second and even the third magnetoacoustic resonance have been identified. Investigation of the radial and axial dependence of Bz at different plasma parameters shows the typical field distribution for geometric resonances. In the upper part of the spectrum, between the third magnetoacoustic resonance and the lower hybrid resonance, a sharp minimum has been observed.

Finite elements ofC1-class on a tetrahedron

Abstract: This paper describes two finite elements of C1-class defined on a tetrahedron. In order to define these elements we give the corresponding function spaces in explicit form.

L'espace vécu chez le peuple Hébreu (à l'époque du retour de l'exil. VI ème siècle avant J.-C.)

Abstract: La maniere d'apprehender l'espace de le de¬ crire, d'agir sur lui, d'Interpreter la rela¬ tion qu'on entretient avec lui varie avec les regions et les epoques. Dans le cadre de ce theme general, les pages qui suivent analysent un cas vieux de 25 siecles: celui du peuple hebreu au retour de sa deportation ä Babylone. Pourquoi ce choix? Nous disposons, gräce ä la Bible, d'une source documentaire ecrite, remontant loin, et d'une richesse teile qu'on s'etonne qu'elle ait ete, sous cet angle precis de la perception spatiale, encore aussi peu exploitee.

A New CAMAC Data Acquisition Interface

Abstract: This article reviews the different types of pulse height analysers and presents their main advantages and disadvantages. The new Camac module offers a solution for hardware problems related with interfacing ADC's to most of the mini-computers. It regulates and derandomises the data flow to the processor, provides a hand-shaking mode between ADC and Central Processor, undertakes a maximum of interface tasks, facilitates the introduction of routing bits and allows the correlation of a number of converters. The design, construction and advantages of this instrument are described and illustrated by examples.