摘要:

AbstractTheN‐diazo coupling ofp‐chloroaniline withp‐chlorobenzenediazonium tetrafluoroborate in acetonitrile at 30° shows non‐linear base catalysis by water. The results are interpreted in terms of theSE2 mechanism with rate‐limiting proton loss at low base concentration; it is postulated, moreover that the reaction proceedsviatransition states in which varying degrees of H‐bonding from the amine and the intermediate ω‐complex to different water species influence the initial step and the

ISSN:0018-019X    

DOI:10.1002/hlca.19810640602

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractIn the title reactions it is shown that aminoazo formation does not occur by direct attack of diazonium ion at C‐atom. Initial attack is at N‐atom, but proton loss from the ωN‐complex formed is relatively slow. Hence, at low amine concentration this rearranges intermolecularly to the aminoazo derivative. At high amine concentration a second method of aminoazo formation can take place involving attack of an amine molecule on the ωN‐complex or on a molecular complex formed between the diazonium ion and the amine. Implication of these proposals for the diazoamino rearrangement are

ISSN:0018-019X    

DOI:10.1002/hlca.19810640603

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractVarious free radicals formed during UV.‐irradiation of aliphatic dicarboxylic acids in aqueous and methanolic solution are identified by ESR.‐spectroscopy. Their structures point to α‐cleavage and photoreduction as the dominant primary photochemical decay processes. The relative contributions of these reactions to the overall photodecomposition depend on solvent and degree of α‐alkylation of the acid. Emission ESR.‐spectra are found for radicals formed by C, CO‐bond cleavage of α‐dimethyl substituted acids. The polarization is referred to the triplet mechanism of CIDEP. and indicates this cleavage reaction occurs from a triplet

ISSN:0018-019X    

DOI:10.1002/hlca.19810640604

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractStreptazolin, a lipophilic neutral compound giving a yellow colour reaction withEhrlichreagent, was isolated from cultures ofStreptomyces viridochromogenes, strain Tü‐1678. On the basis of a “chemical screening”. Its structure,1, was determined by spectroscopic investigations and chemical degradations. Dihydrostreptazolin3exhibits limited antimicrobial activities. Pharmacological investigations are in pr

ISSN:0018-019X    

DOI:10.1002/hlca.19810640605

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

Vinylogous β‐Cleavage of Epoxy‐enones: Photoisomerization of 3,4: 5,6‐Diepoxy‐5,6‐dihydro‐β‐iononeOn1n,π*‐excitation (λ>347 nm), 3,4:5,6‐diepoxy‐5,6‐dihydro‐β‐ionone ((E)‐3) shows the typical behaviour of α,β‐unsaturated γ,δ‐epoxy ketones furnishing the(Z)‐enone3and by C(γ),O cleavage of the oxirane the dihydrofuryl ketone10and the cyclohexanones(E/Z)‐11. However, on1π,π*‐excitation an unexpected type of transformation is observed:(E)‐3is isomerized to the four aliphatic triketones5–8as the main products. To a smaller extent the allene diketone9is formed by a known type of isomerization as well as(Z)‐3.As the starting material for the preparation of(E)‐3, the known epidioxy‐enone(E)‐4was used. In addition to(E)‐3,(E)‐4gives the aliphatic trik

ISSN:0018-019X    

DOI:10.1002/hlca.19810640606

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

Abstract4,2‐Chloronitrobenzenediazonium ions in aqueous buffer solutions between pH 2.9 and 7.9 do not hydrolyze by dediazoniation as previous authors have assumed, but by denitration. The isomeric 2,4‐compound reacts by denitration (ca. 70%) and dechlorination (ca. 30%). The reactions are general base catalyzed. The products and kinetics are consistent with anSNAr‐mechanism in which the general base‐catalyzed addition of a hydroxyl group at the reacting C‐atom is rate‐limiting. The rate maxima at or near the pH‐values corresponding to (pK1+ pK2)/2 of the diazonium ⇄cis‐diazotate equilibria can be rationalized on the assumption that the diazonium ion is the only equilibrium form of the diazo compound which enters the substitution proper, and the superposition of the rate term B∑kB[B] of all nucleophiles involved (H2O,

ISSN:0018-019X    

DOI:10.1002/hlca.19810640607

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractThe complex formation of some divalent 3d‐ and trivalent 4f‐metal ions with four macrocyclic ligands has been investigated in methanol/water 95:5 by use of alkalimetric titrations. In contrast to alkali and alkaline‐earth cations the obtained stability constants are quite low. The reasons of this effect are disc

ISSN:0018-019X    

DOI:10.1002/hlca.19810640608

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

Revised Structure of the Macrodiolide ColletodiolAn X‐ray analysis shows that the vicinal glycol unit of colletodiol has thethreo‐rather than the previously assignederythro‐configuration (see1,Fig. 1andFig. 3). Together with the correlative assignments of (2R)‐ and (8R)‐absolute configurations byMacMillan&Simpsonthe centers of chirality of colletodiol1are now established to be (2R, 8R,

ISSN:0018-019X    

DOI:10.1002/hlca.19810640609

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractTriplet state formation (Φisc) and properties (εT‐T, τT) of phthalocyanine (HPC) and zinc phthalocyanine (ZnPC) have been characterized in homogeneous solutions (1‐chloronaphthalene, 1‐propanol) and in microemulsion by investigating the variation of the transient optical density as a function of the intensity of the exciting laser. Experimental results follow the theoretically predicted dependence only for very low intensities of the exciting pulse. At higher intensities, a more complicated scheme of primary reactions has to be taken into account, implicating qualitative restrictions in the application of saturation experiments. The observed transients at high‐intensity excitation are interpreted as being perturbed by aggregational

ISSN:0018-019X    

DOI:10.1002/hlca.19810640610

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

A Ring Enlargement Reaction with a BarbiturateThe (6‐membered) barbituric acid derivative3was synthesized and treated with KF/DMF/18‐crown‐6 to form the ring‐enlarged 14‐membered compound8in g

ISSN:0018-019X    

DOI:10.1002/hlca.19810640611

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY