摘要:

AbstractThe factors influencing the ease of the lithium aluminium hydride reduction of various 1,2‐epoxycycloalkanes and 1,2‐epoxyalkanes are described and discus

ISSN:0018-019X    

DOI:10.1002/hlca.19760590702

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

Identification of alkyl‐5H‐6,7‐dihydrococyclopenta[b]pyrazines in roasted meat flavor. Model reaction used as basis for natural product formation and new synthesis.Seven alkyl‐5H‐6,7‐dihydrocyclopenta[b]pyrazines have been identified in a roasted meat aroma obtained by thermolysis of the hydrosoluble flavor precursors of raw meat. Formation of these heterocyclics by condensation of hydroxycyclopentenones with aliphatic α‐dicarbonyl compounds in the presence of ammonia has been confirmed by a model reaction.Alkyl‐5H‐cyclopenta[b]pyrazines and dicyclopenta [b,e]pyrazines are also obtained from this reaction, but have not yet been identified in roasted flavors. Preparation of the intermediates of the model reaction enabled development of an economical synthesis of 2,3,5‐trimethyl‐5H‐6,7‐di

ISSN:0018-019X    

DOI:10.1002/hlca.19760590703

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

Synthesis of alkyl‐5H‐cyclopenta[b]pyrazines.Alkyl‐5H‐cyclopenta[b]‐pyrazines (sometimes together with 5‐alkylidene‐5H‐6,7‐dihydrocyclopenta[b]pyrazines) are prepared by thermal degradation of 5‐acetoxy‐5H‐6,7‐dihydrocyclopenta[b]pyrazines; these are obtained by treatment of alkyl‐5H‐6,7‐dihydrocyclopenta[b]pyrazineN‐oxides with acetic anhydride. Cyclopenta[b]pyrazines which are potentially present in roasted food flavors possess in

ISSN:0018-019X    

DOI:10.1002/hlca.19760590704

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

13C‐NMR. Studies on Ion‐Selective Liquid Membranes.A method for the13C‐NMR. study of solvent polymeric membranes in equilibrium with aqueous salt solutions is described. Neutral ion carriers incorporated in these membranes maintain a high degree of rotational mobility. The complexation by group IA and IIA cations of macrotetrolide antibiotics as well as of carriers of the type 3,6‐dioxa‐octanedioic diamides in the membrane phase was followed by13C‐NMR. chemical shift and spin‐lattice relax

ISSN:0018-019X    

DOI:10.1002/hlca.19760590705

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe linear free energy relationship ofSicherfor relative reactivity towards chromic acid oxidation (ΔΔG Ox≠) as a function of thermodynamic stability (ΔG eq0) has been reexamined with 23 pairs of epimeric alcohols. The plot of ΔG Ox≠vs. ΔG eq0has a slope of 0.8, a correlation coefficient of 0.97 and a standard deviation of 0.23 kcal/mol on ΔΔGOx Ox≠. The limitations of the relationship and the ex

ISSN:0018-019X    

DOI:10.1002/hlca.19760590706

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

Acetoxytropyliumbromide: Synthesis, Structural Evidence, Behaviour in Solution.Acetoxytropyliumbromide (9) is formed from tropone and acetylbromide. In solution the tropylium salt equilibrates with the educts,9being favored at low temperature in polar aprotic solvents. The structure of the title compound has been proved by X‐ray analysis, as well as by investigation of the1H‐NMR. spectra of solutions

ISSN:0018-019X    

DOI:10.1002/hlca.19760590707

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

AbstractThe addition of difluorocarbene to bicyclo[2.2.2]octa‐2,5‐diene gave theexoandendo1:1 cyclopropane adducts. In contrast to norbornadiene, nohomo‐1,4 adduct was formed. The adducts were thermally stable under the conditions of their formation and separation (<170°). However, smooth equilibration was achieved on heating at 250° for 36 h. The same mixture resulted from either isomer. At 250° ΔΔG= 1.83 kcal/mol; theendoisomer being the more stable. Heating to higher temperatures caused decomposition, rather than further reaction to the intramolecular [2+2]cyclization products. The kinetic and thermodynamic product compositions were essentially the same on extrapolating to the same temperature, viz.endo/exo= 19–22 at 25°. The mechanisms by which the cyclo‐addition and the stereomutation of thecis‐fused cyclopropane moiety oc

ISSN:0018-019X    

DOI:10.1002/hlca.19760590708

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

Mechanistic studies on the photochemistry of 2‐alkylindazoles in aqueous solutions.The photochemistry of 2‐alkylindazoles1in aqueous solutions is rather complex, the relative yields of different products being dependent on the pH‐value of the irradiated solution: In neutral or basic solutions (pH>7) as well as in most of the organic solvents isomerization to 1‐alkyl‐benzimidazoles2takes place. In dilute sulfuric acid (pH 2–4) this reaction is suppressed and the dihydro‐azepinones3and4are formed. Irradiation in strongly acid solutions (pH<1) yields theo‐amino‐acetophenones5(Scheme 1).The relative quantum yields of the photoproducts2–5have been measured as a function of the pH‐value of the irradiated solution (Fig. 1). A comparison of these yields with the protonation equilibrium of the indazole in its first excited singlet state (pK= 2.8) suggests that2and3are both photoproducts of the neutral indazole molecule, whereas4as well as5are formed from the protonated indazole.The rearrangement of the indazole1to the benzimidazole2proceedsviaan intermediate6, which can be produced in high concentrations by monochromatic irradiation of1at low temperatures. The thermal reactivity of this intermediate in dilute sulfuric acid could be investigated: At pH 8 the only product is the benzimidazole2. With decreasing pH‐value increasing amounts of3are formed and at pH<4 the formation of2is completely suppressed, the only product being the azepinone3. Thus,3is a solvolysis product of the intermediate6(Scheme 2).The most probable primary product of singlet indazolium is the nitrenium ion7. From this intermediate the formation of5can proceed in well‐known thermal reactions. The formation of4is possibly due to a further protonation equilibrium nitrenium‐nitrene. The nitrene7can be converted into the azepinone4viathe azirine8(Scheme 3). The pK‐values of different indazoles and intermed

ISSN:0018-019X    

DOI:10.1002/hlca.19760590709

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

The crystal structure of xanthopterine‐hydrochloride.The crystal structure of the title compound, a pterine, has been determined by X‐ray analysis (direct methods) and refined with 1332 structure amplitudes toR= 0.027. The crystal system is monoclinic, space groupP21/c, with unit cell dimensionsa= 7.942,b= 8.417,c= 12.076 Å, β = 93.77°. The molecule is protonated at the N(1)‐position. The angle between the planes of the pyrimidine and pyrazine rings

ISSN:0018-019X    

DOI:10.1002/hlca.19760590710

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY

摘要:

Configuration and conformation of 6,7‐Dimethyl‐ and 5,6,7‐Trimethyl‐5,6,7,8‐tetrahydropterines.During the hydrogenation of 6,7‐dimethylpterine,cis‐6,7‐dimethyl‐tetrahydropterine is formed. A possible conformation for this substance and for the 5,6,7‐trimethyl derivative, which is obtained from it, is discussed, taking the1H‐NMR. spectra of both tetrahydropterin

ISSN:0018-019X    

DOI:10.1002/hlca.19760590711

出版商:WILEY‐VCH Verlag GmbH    

年代:1976

数据来源: WILEY