摘要:

AbstractStarting from a selectively protected derivative of α,α′‐diaminosuberic acid (3) the linear protected peptide11has been obtained. Cyclisation to12followed by removal of the protecting groups by hydrogenolysis afforded the ‘dicarba’ analogue of oxytocin,1 c, which showed about 5 IU/μmol of uterotonic activi

ISSN:0018-019X    

DOI:10.1002/hlca.19740570502

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractHomo‐p‐chinon (4= Bicyclo[4.1.0]hept‐3‐en‐2,5‐dion) wurde hergestellt und auf seine Spektraleigenschaften untersucht. Die UV.‐, IR.‐ und NMR.‐Spektren sind charakteristisch für die darin enthaltene Endion‐undcis‐disubstituierte Cyclopropan‐Substruktur, ohne eine starke Wechselwirkung zwischen den beiden zum Ausdruck zu bringen.Basische Thermolyse des Bis‐p‐toluolsulfonylhydrazons (9) von Homo‐p‐chinon ergab das bekannte 1,7 a‐Diaza‐inden (10). Dies bestätigt den früher postulierten Mechanismus derBamford‐Stevens‐Reaktion mit den z

ISSN:0018-019X    

DOI:10.1002/hlca.19740570503

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractThe photoelectron spectra of 1,5‐cyclooctadiyne (2) and of 1,6‐dithiacyclodeca‐3,8‐diyne (3) have been recorded. The first four (2) or six (3) PE. bands have been assigned as follows; in increasing order of ionization potentials:\documentclass{article}\pagestyle{empty}\begin{document}$$ 2:\,2{\rm b}_{{\rm 2g}} (\pi),\,6{\rm b}_{{\rm 1u}} (\pi),\,7{\rm a}_{\rm g} (\pi),\,2{\rm b}_{{\rm 3u}} (\pi) $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ 3:\,14{\rm a}_{\rm g} ({\rm n}),\,9{\rm a}_{\rm u} (\pi),\,13{\rm b}_{\rm u} ({\rm n}),\,12{\rm b}_{\rm u} (\pi),\,8{\rm b}_{\rm g} (\pi),\,13{\rm a}_{\rm g} (\pi) $$\end{document}The relative sequence and the positions of the PE. bands are explained in terms of through‐bond and through‐space interactions between the basis π‐orbitals and σ‐orbitals of appropriate symmetry behaviour.An analysis of the PE. spectroscopic data for cyclooctyne (1) and for (2) indicates that acis‐bend of the acetylene moiety by θ<20° leads to a split in energy of the in‐plane and out‐of‐plane basis π‐orbitals which is smaller than ∽ 0.2 eV. This is in agreement with the predictions derived from semiempirical models (MINDO/2, SPINDO) and qualitative orbital arguments. However, it is shown by using orbital localization procedures, that the rationales underlying the two semiempir

ISSN:0018-019X    

DOI:10.1002/hlca.19740570504

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractThe photochemical reactivity of the title compound3was studied in the context of a novel acid catalysed photocyclisation reaction recently discovered byBarton et al.[1b]. The following results were obtained by flash photolysis methods and steady state irradiations in the presence and absence of quenchers and sensitisers combined with luminescence measurements: The fluorescence of3in benzene is very weak and short‐lived (ϕF1≤ 10−4, τF1≤ 10−9s) due to efficient intersystem crossing (ϕT= 0.8 ± 0.15). On the other hand, the conjugate acid4exhibits an intense green fluorescence (ϕF1= 0.97± 0.1) with a lifetime of (4. ± 1.) · 10−9s. Acidity constants of4in the ground and first excited triplet state were estimated in acetic/trifluoroacetic acid mixtures by comparison withHammettindicators: pK(S0) = −0.3, pK(T1) = +1.TheFörstercycle yields pK(S1) = +6, however, adiabatic protonation of S1(3) to produce fluorescent4is not efficient. The lowest ππ*triplet state of3(ET= 45 ± 1 kcal/mol,3τ = 8 · 10−4s in dilute, degassed benzene solution) is an intermediate in the photoreduction of3by oxidisable substrates. Hydrogen abstraction from 2‐propanol by T1(3) yields the semiquinone methide radical5which dimerises to6. On readmission of air after irradiation,6is reoxidised to the starting material3. Predictions derived from PPP SCF CI calculations are in accord with the observed spectroscopic a

ISSN:0018-019X    

DOI:10.1002/hlca.19740570505

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractA total of 68 constitutents, mainly aldehydes, ketones and esters, have been identified for the first time in a black tea aroma concentrate using coupled gas‐chromatography/mass spectrometr

ISSN:0018-019X    

DOI:10.1002/hlca.19740570506

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractThe reaction between (Z)‐1‐alkenyllithium and (E)‐β‐(N, N‐dialkylamino)‐α, β‐alkenals, (E)‐β‐(N, N‐dialkylamino)‐α, β‐alkenones or (E)‐β‐(N, N‐dialkylamino)‐α, β‐alkenoic esters yields mainly (E, Z)‐α, β‐γ, δ‐diunsaturated aldehydes, keton

ISSN:0018-019X    

DOI:10.1002/hlca.19740570507

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractThe magnesium 3,3‐dimethylcyclohex‐1‐enolate1i, formed in the copper catalyzed addition of methylmagnesium iodide to 3‐methylcyclohex‐2‐enone, has been subjected to regiospecific electrophilic reactions such as acylation, alkylation, and aldol condensation in order to find a new access to the damascones, ionones and carotenoids. By way of illustration a new synthesis of γ‐damascon

ISSN:0018-019X    

DOI:10.1002/hlca.19740570508

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractThe formation and dissociation kinetics of the pentaco‐ordinated Cu2+, Ni2+, Co2+and Zn2+complexes with 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane (4‐MeCyclam‐14) was studied by pH‐stat techniques and spectrophotometrically. The rates of the reactions between 4‐MeCyclam‐14 and each of the four metal ions, although slower than normal complexations by a factor of 103−104, closely follow the order Cu2+>Zn2+>Co2+>Ni2+, found for the rate of water exchange. This implies that beside water exchange an other constant factor plays an important role in the rate determing step. The dissociation of the pentaco‐ordinated 4‐MeCyclam‐14 complexes is acid catalyzed. The limiting rate for acid dissociation is not reached even in 2.5MHNO3in the case of Ni(4‐MeCyclam‐14)2+. From the formation and dissociation rates stability constants have been calculated, which do no

ISSN:0018-019X    

DOI:10.1002/hlca.19740570509

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractThe mass spectra of the O‐isopropylidene derivatives ofthreo‐ anderythro‐furanose and those of the four C(4) methylated stereoisomers have been studied. Fragmentation modes based upon deuterium labelling, metastable peaks and high‐resolution measurements are proposed. Each stereoisomer can be characterized by its low‐resolution mass

ISSN:0018-019X    

DOI:10.1002/hlca.19740570510

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY

摘要:

AbstractThe complex formation of Hg2+, CH3Hg+and C6H5Hg+with eight substituted quinolines, α,α′‐bipyridyl and 1, 10‐phenanthroline has been investigated in water and 75(v)% dioxane by pH and pHg methods. Hg2+forms mercurated products with 8‐hydroxyquinolines, if the 5‐ or 7‐positions are unsubstituted. The formation of chelates by CH3Hg+and C6H5Hg+

ISSN:0018-019X    

DOI:10.1002/hlca.19740570511

出版商:WILEY‐VCH Verlag GmbH    

年代:1974

数据来源: WILEY