摘要:

AbstractTheSchiffbase of all‐trans‐retinal was investigated in organic solution by1H‐ and13C‐NMR. at high field. Complete assignment of the1H‐NMR. peaks ofN‐butyl‐(all‐trans‐retinylidene)amine (2) and theN‐butyl‐(all‐trans‐retinylidene)‐ammonium ion (3) was achieved by INDOR (internuclear double resonance). The vicinal proton coupling constants of the polyene chain show that the π‐bond orders remain unchanged inN‐butyl‐(all‐trans‐retinylidene)amine relative to all‐trans‐retinal (1), but change towards larger π‐delocalization in theN‐butyl‐(all‐trans‐retinylidene)ammonium ion. At −‐61° only one isomer ofN‐butyl‐(all‐trans‐retinylidene)ammonium was observed. This was shown to betransat the imine linkage and independent of the solvent. The trifluoroacetic acid counter‐ion can approach the positive charge of the N‐atom in the weakly polar solvent dichloromethane but not in the leveling solvent methanol. In dichloromethane the nature of the 1:1 complex is a H‐bonded (O−…H‐N+) ion‐pair whose rate of breaking and forming is rapid at RT. Strong stabilization of the ion‐pair resulted from homo‐conjugation with a second molecule of trifluoroaceti

ISSN:0018-019X    

DOI:10.1002/hlca.19810640702

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

Abstract3,5‐Octadiyne cation in its lowest excited state has been studied in the gas phase by laser‐induced fluorescence and photoelectron‐photon coincidence techniques. The excitation spectrum of the Ã2″←2A″ transition has been obtained and yields vibrational frequencies of some of the fundamentals for the excited cationic state. The fluorescence quantum yields and lifetimes at selected energies within the Ã2A″ state have been determined from the coincidence measurements. This provides quantitative data for the discussion of the relaxation behaviour of such an excited op

ISSN:0018-019X    

DOI:10.1002/hlca.19810640703

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractThe photoelectron (PE.) spectra of thirteen methyl‐substituted [2.2]paracyclophanes have been recorded and analyzed, to assess the influence of methyl‐substitution on their ionization energies. It is shown that this influence is qualitatively and quantitatively the same as for benzenes and other π‐systems. Comparison with the previous results obtained for the [2r]cyclophanes (r=2 to 6) strongly suggests that the hyperconjugative model for alkyl‐group/π‐system interactions is more appropriate than the in

ISSN:0018-019X    

DOI:10.1002/hlca.19810640704

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractDeprotonation of the 3‐trialkylsilyloxy‐1,4‐diene3aand subsequent electrophilic substitution of the non‐isolated 3‐trialkylsilyoxypentadienyllithium4gives the α‐ and γ‐products8and/or6in good yields. Whereas alkylation of4proceeds with variable regioselectivity(Table 1)aldehydes and ketones attack preferentially the γ‐position of4(Table 2). The desired γ‐products6may be directly subjected to inter‐ and intramolecular [4 + 2]‐additions as demonstrated by the reactions5a(6d) →7and6h→19(Schemes 4and12). Alternatively, smooth fluoride‐promoted silylether‐cleavage6→11(Scheme 8)provides a convenient approach to substituted vinyl ketones such as to the natural products11f(Table 3). The stereoselective conversion6k→23(Scheme 13)implies anendo‐selective intramolecularDiels‐Alderaddition (26→23) and exemplifies the use of4as an equivalent of the hypothetical anionIV. Furthermore, some electrophilic substitutions of the he

ISSN:0018-019X    

DOI:10.1002/hlca.19810640705

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

Abstractγ‐Selective sulfenylation of the triethysilyloxypentadienyllithium1gave the versatile alkylthiodene4which on successive deprotonation and alkylation furnished with high regioselectivity the γ‐products6. Fluoride‐promoted silylether cleavage6→7may be followed by intramolecular [4 + 2]‐addition7c→8and sulfoxide elimination8→9. The conversions7b→12and7a→17demonstrate the feasibility of5to serve as an equivalent of the hypothetical β‐deprotonated divinylketone13whose two enone units may

ISSN:0018-019X    

DOI:10.1002/hlca.19810640706

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractA tentative assignment is proposed for the He (Ia) photoelectron (PE.) spectra of the title compounds. It is based on the assumption that the first four π‐bands occupy the same position in both spectra, as suggested by a qualitative correlation with the PE. spectrum of [24](1,2,4,5)cyclophane and by a previously proposed molecular orbital model. If this is accepted, then the bands due to electron ejection from the lone‐pair orbitals are split by roughly 0.8 eV in the case of the 4, 13‐diaza isomer, whereas no split can be detected in the case of the 4, 16‐diaz

ISSN:0018-019X    

DOI:10.1002/hlca.19810640707

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractA surfact derivative of phenothiazine was synthesized which is capable of micelle formation in aqueous solution. Concomitantly with micellization, strong changes in the photochemical behaviour occur. In particular, monophotonic photoionization is only observed above the critical micelle concentration (CMC.). Cooperative effects associated with self‐assembly of this amphiphilic redox chromophore leading to local electrostatic barriers are evoked to explain these effect

ISSN:0018-019X    

DOI:10.1002/hlca.19810640708

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractIt has been demonstrated that the triplet lifetime of nonemitting molecules in the dilute vapor phase ‐ even for complex triplet decays ‐ can be accurately determined by means of time‐resolved triplet‐triplet (T‐T) energy transfer to a strong emitter molecule. Besides the test molecules 1‐butyne‐3‐one and benzaldehyde the lifetime of the vibrationally relaxed nonemitting T1(nπ*) state of cycloheptanone, τ=63 ± 5 µs at ∼︁0.5 Torr, together with its energy transfer rate constant to biacetyl,kET=(1.80±0.08) x 106s−1

ISSN:0018-019X    

DOI:10.1002/hlca.19810640709

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractTwo new metabolites have been isolated from cultures ofChaetomium globosum. The structures of 19‐O‐acetylchaetoglobosin B (4) and 19‐O‐acetylchaetoglobosin D (5) are assigned. The13C‐NMR. spectra of chaetoglobosin A (1), 19‐O‐acetylchaetoglobosin A (2), chaetoglobosin C (3), 19‐O‐acetylchaetoglobosin B (4), 19‐O‐acetylchaetoglobosin D (5) and of cytochalasin G (6), a (3‐indolyl)‐[11]cytochalasan isolated fromPseudeurotium zonat

ISSN:0018-019X    

DOI:10.1002/hlca.19810640710

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY

摘要:

AbstractIncorporation of [1‐13C]‐, [2‐13C]‐ and [1,2‐13C2]‐acetate, [1‐13C]‐propionate, [13C‐CH3]‐L‐methionine and [3‐14C]‐DL‐tryptophan into chaetoglobosin A (1) and 19‐O‐acetylchaetoglobosin A (2) byChaetomium globosumdemonstrated that the building blocks of1and2are 9 and 10 units of acetate/malonate respectively, 3 units of methionine and 1 unit of tryptophan. Propionate is incorporated indirectly after several biological transformations. Using [2‐13C, 2‐2H3]‐acetate as precursor, the starter unit of the polyketide‐chain was identified. Experiments which [13C,2H3‐CH3‐L‐methionine demonstrated that the threeC‐methylations occur with retention of all three H‐atoms of the methyl group. Incorporation experiments with various14C‐ and3H‐labelled tryphtophan samples and with [2‐2H]‐ and [2‐15N]‐L‐tryptophan showed that the amino acid is incorporated intact with retention of both the α‐H‐ and the α‐N‐atom. On the basis of these results

ISSN:0018-019X    

DOI:10.1002/hlca.19810640711

出版商:WILEY‐VCH Verlag GmbH    

年代:1981

数据来源: WILEY