ISSN:0018-019X    

DOI:10.1002/hlca.19820650102

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

The Avileurekanoses A and C and Further Degradation Products of the Avilamycins A and CAlkaline hydrolysis of the orthosomycin antibiotics, avilamycins A ad C products similar t those earlier described for flambamycin. Among these avileurekanose c (15) became of particular importance because its acetate prisms suitable for an X‐ray structural determination. For the avilamycins A and C structural formulae2and3, respectively, can now be drawn, in which only the configuration at C (16), one out of 32 asymmetric C‐atoms, is not yet determi

ISSN:0018-019X    

DOI:10.1002/hlca.19820650103

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

Spezifitäten der α‐Alkinon CyclisierungDie Regio‐ und Stereo spezifitäten der α‐Alkinon‐Cyclisierung, einer thermischen Umwandlung von Alkinyl‐alkyl‐ketonen, welche in β′‐Stellung mindestens ein H‐Atom tragen, zu 2‐Cyclopentenonen wurden untersucht. Cyclisierung zum höher substituierten C(β′)‐Atom ist dabei bevorzugt, vorausgesetzt, dass die zur Insertion zur Verfügung stehende C(β′), H‐Bindung zur Propioloylseitenkette eine möglichst synplanare Anordnung einnehmen kann. In Cyclisierungen zu β′‐Methylen‐C‐Atomen, welche diastereotope H‐Atome tragen, wird daher eines der möglichen epimeren Produkte bevorzugt oder ausschließlich gebildet. Die mechanistischen Konseque

ISSN:0018-019X    

DOI:10.1002/hlca.19820650104

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractThe103Rh‐resonance has been investigated at 2.8 MHz in mono‐ and dinuclear olefin complexes by steady‐state NMR.‐pulse techniques. For dirhodium complexes with scalar Rh, Rh‐coupling, a selective rf‐irradiation was applied to improve sensitivity. Within the same measuring time the signal/noise ratio is improved by the factor (T2/T 2*)1/2by this steady‐state method in comparison with the usual free‐induction technique. (T1/T2)‐ratios, as obtained from the dependence of signal in tensity on the pulse‐flip angle are discussed in terms of relaxation mechanisms and chemical exchange phenomena. From (T1/T2)‐ and (T1+ T2)‐experiments, individual T1and T2values have been determined for C5H5RhC8H12and Rh(acac)3.The 103Rh‐chemical shifts of 39 olefin complexes are reported. Shielding depends upon the (formal) oxidation state of Rh whereby resonances of pure olefin complexes appear at the low‐frequency end of the δ‐scale, which extends over 10000 ppm. For cyclic 1,3‐diene ligands Rh‐shieldingincreaseswithdecreasing ringsize anddecreaseswith further conjugation of the diene systems.In the dirhodium complexes, Rh, Rh spin‐coupling constants are<10 Hz. Rh, C‐coupling constants in (diene)RhCp‐complexes increase, for the terminal diene C‐at om, with increasing ring size

ISSN:0018-019X    

DOI:10.1002/hlca.19820650105

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractThe complexation of Cue2+with 1, 8‐diamino‐3, 6‐diaza‐2, 7‐octanedione (N, N′‐diglycyl‐1, 2‐ethanediamine, DED) and with 1, 9‐diamino‐3, 7‐diaza‐2, 8nonanedione (N, N′‐diglycyl‐1, 3‐propanediamine, DPD) has been studied by potentiometric and by spectrophotometric titration. With both ligands L the complexation to Cue2+leads to relatively complicated equilibria with CuLH3+, CuL2+, CuLH−2, and dimeric Cu2L 24+complexes. With DED, another dimeric species, Cu2L2H −22+, is formed in addition. Independent numerical treatment of spectrophotometric and poteritiometric titrations was used to obtain a satisfactory model for the complexation and to test the relative discriminatory power of the two methods. Titrations of glycine ethylamide (GEA) were used as an additional test and as a model for DED and DPD. It was shown that in each case spectrophotometric titrations give results of similar reproducibility and have a discriminatory power equal to or better than potentiometric titrations, provided that optimum mathematical a

ISSN:0018-019X    

DOI:10.1002/hlca.19820650106

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractN, N‐Dioctadecyl‐substituted lipophilic monoamides of certain dicarboxylic acids have been prepared. It is shown that they induce a transport of alkaline earth metal cations through solvent polymeric membranes coupled to a counter transport of hydrogen ions or K+. They proved to be suitable components for ion‐selective elect

ISSN:0018-019X    

DOI:10.1002/hlca.19820650107

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractWith conventional phase‐transfer catalysis using quaternary ammonium salts, yields of 2, 4‐dinitrobenzenesulfonic acid (2) in the sulfodechlorination of 1‐chloro 2.4‐dinitrobenzene (1) with sulfite ions are no better than those obtained with the classical method in aqueous ethanol (80–82%). Yields up to 97% and a very pure product are obtained, however, by using protonated tertiary amines as catalysts. The optimum chain‐length of the amine is found with tributylamine. On mixing solutions of the reagents and catalysts a strong bluish‐red colour develops immediately, but disappears withinca.1 h. Comparison of the NMR. spectrum of this primary product with model adducts of sulfite ions and di‐ and trinitrobenzene derivatives demonstrates that the primary addition of the nucleophile to 1‐chloro‐2, 4‐dinitrobenzene does not take place at C (1), but at C(5). It is shown that the increments calculated for a C sp 3‐SO 3−group and for the 1, 3‐dinitro‐ and 1, 3, 5‐trinitropentadienyl ring moieties can be employed for the approximate calculation of1H‐chemical shifts usingClerc&Pretsc

ISSN:0018-019X    

DOI:10.1002/hlca.19820650108

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

Fulvene‐Dieters: Synthesis, Structure Elucidation and Thermal BehaviourIn contrast to earlier assumptions, thermal reaction of pure fulvene (1a), 6‐methylfulvene (lb) and 6, 6‐dimethylfuivene (1c) at 227deg; gives oligomeric mixtures consisting mainly of theendo‐[4 + 2]‐eycloaddition products2a,2band2c. Thermal reactivity of the fulvenes decreases strongly in the series1a>1b>1c. While the dimers2band2cequilibrate very easily in solution above room temperature with1band1c, respectively,2aequilibrates with the isomer5a(1, 6‐Dimethyliden3a α, 3bβ, 6a α, 6bβ‐tetrahydro‐1‐H), 6H‐bi (cyclopentadienylen). This surprising rearrangement envolves a formal 1,3‐shift of the 1, 2‐dihydro

ISSN:0018-019X    

DOI:10.1002/hlca.19820650109

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

Structure Elucidation of a Dimethylfulvene‐trimer. Evidence for a [6+ 4]‐Dimerization of 6, 6‐DimethylfulveneThermal reaction of pure 6, 6‐dimethylfulvene (1c) at 60° gives an oligomeric mixture consisting mainly of fulvene‐trimers. The structure of the main product3cis partially elucidated by1H‐NMR. investigations at 400 MHz and definitely confirmed by X‐ray analysis. The formation of3cis explained in terms of a [6+4] dimerization, followed by a 1, 5‐proton‐shift and a finalD

ISSN:0018-019X    

DOI:10.1002/hlca.19820650110

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY

摘要:

AbstractThe effect ofKékulérepresentation and hybrid function of O‐atoms in the PCILO‐CNDO framework of conformation and internal rotation in mono‐sub stituted benzenes Ph‐X (XNH2, OH, OCH3, CH3, CHO, NO2) is studied. Three variational criteria for the choice of the appropriate third‐order energy, proposed to symmetrize the PCILO results, are critically examined in relation with the height of rotational barrier in these molecules. The study shows that, in all cases, the most stable conformation is qualitatively correct predicted by the PCILO method. Since the barrier to internal rotation in the studied aromatic systems arises predominantly from delocalization effect, it is proposed to employ the arithmetic mean of the third‐order energy of the twoKékuléstructures. In molecules, in which the third‐order energy between the twoKékuléstructures is larger than 2 kcal/mol, however, the lower third‐order energy representation alone seems to be appropriate. In phenol and anisole the spa‐hybridization type of the O‐atoms offers better values of rotational barrier, whereas in the sp3‐type the delocalization is overestimat

ISSN:0018-019X    

DOI:10.1002/hlca.19820650111

出版商:WILEY‐VCH Verlag GmbH    

年代:1982

数据来源: WILEY