GLORIA

GEOMAR Library Ocean Research Information Access

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • 1980-1984  (8)
Document type
Keywords
Publisher
Year
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 729-741 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XVIII. 2-Alkoxy-2H-pyrans from Tetra- and Pentasubstituted Pyrylium SaltsAlkali alkoxides add regioselectively to 2,3,4,6-tetrasubstituted pyrylium salts 7 (R'= H), affording high yields of colourless crystalline 2-alkoxy-2H-pyrans 9. The latte are also formed simply on refluxing 7 in the corresponding alcohol with triethylamine as proton acceptor. 3,5-Dialkylsubstituted 2,4,6-triarylpyrylium salts react analogously. The 2H-pyran structure of the adducts obtained follows from their n.m.r., i.r., u.v. and mass spectra as well as from their reaction with tetracyanoethylene to cycloadducts of type 10. Acids regenerate from 9 the original pyrylium cations, whereas reaction of 9 with nitromethane or ethyl cyanoacetate provides benzene derivatives. -- The novel starting pyrylium salts 7b--o are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 955-961 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXV. Quantum Chemical Calculations Concerning the Valence Isomerization of 2-Amino-2H-pyran and -thiopyranThe equilibrium 2-amino-2H-pyran 6 ⇌ 5-amino-2,4-dien-1-one 7 was investigated using the semi-empirical MINDO/3 and MNDO methods. In accordance with experimental findings for the substituted derivatives 1/2a-d, the introduction of a methyl group into the position 3 of 6 or the exchange of oxygen by sulfur shifts the equilibrium towards the cyclic structures 8 and 10, respectively. Polar solvents, the influence of which was estimated applying the reaction field approach as well as the solvaton theory, and entropy effects are calculated to favour the ring-open valence isomer 7. These results also correspond to experimental results.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 287-302 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXI. Structure and Tautomerism of Pseudobases of Unsymmetrically Substituted 2,4,6-Triarylpyrylium SaltsHydrolytic ring opening of unsymmetrically substituted 2,4,6-triarylpyrylium salts 11 results in a mixture of two tautomeric pseudobases, the penten-1,5-diones 13 and 14. In crystalline state as a rule one of these tautomers markedly predominates, whereas in solution a rapid equilibrium establishment occurs which can be followed by 1H-n.m.r. and u.v. spectroscopy (equilibrium ratio nearly 1:1). The 1H-n.m.r. spectroscopic structural assignment of the two isomeric forms was supported by u.v. spectroscopic studies using 1:1 mixtures of the chromophoric partial systems ArCOCH=CHPh and ArCOMe or the pseudobases 10 of symmetrically substituted 2,4,6-triarylpyrylium salts 9 as reference systems. From the mass spectra of the pseudobases 10 and 13/14 follows that - if hydrolysis of 11 is performed in media containing H218O - mass spectrometric isotopic analysis of the resulting 18O-labelled pseudobases allows no information to be made about the regioselectivity of the ring opening. - Novel starting pyrylium salts of type 9 and 11 are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 647-656 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXII. 1H-N.M.R. and U.V. Spectroscopic Investigations on the Isomerization of Pseudobases of Unsymmetrically Substituted 2, 4, 6-Triarylpyrylium SaltsThe kinetics and mechanism of the isomerization of the title compounds, the pentene 1,5-diones 2 and 3, were studied by 1H-n.m.r. and u.v. spectroscopy. The equilibrium constants measured vary little near 1, indicating the small influence of substituents on the equilibrium position. The mutual rearrangement 2⇄3 proved to be a base-catalized reaction which is characterized by strictly linear Hammett correlation between 1g k and Σσp. The results obtained suggest resonance-stabilized anions of type4 as intermediates. - Pseudobases of 3-alkyl-2, 4, 6-triarylsubstituted pyrylium salts do not undergo a reversible isomerization.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 322 (1980), S. 229-236 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic Phosphorus Compounds. XIII. Reaction of Vinylogous Chloromethylene Immonium Salts with Trialkyl Phosphites3-Chloropropenylidene immonium salts of the type Cl—CAr=CH—CH=NMe2⊕X⊖ don't react like chloromethylene immonium salts Cl—CH=NMe2⊕X⊖ with trialkyl phosphites according to the classical MICHAELIS-ARBUSOV principle (RO)3P + R′Cl → (RO)2P(O)R′ + RCl but lead to salts of 1-dimethylaminophosphonates (RO)2P(O)—CH(NMe2 · HX)—CH=CClAr the structure of which is confirmed by two independent syntheses. Some characteristic reactions of the free dimethylaminophosphonates are described.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 322 (1980), S. 99-124 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vinylogous Acyl Compounds. XIX. Vinylogous Acyl Group Migration in 2-Aminophenol. A Contribution to the Isomerization Mechanism of Mixed Diacyl Derivatives of 2-AminophenolStarting with 2-acylaminophenols 5 and 2-(2-acylvinylamino)-phenols 6 the N-acyl O-acylvinyl derivatives 7 of 2-aminophenol and their N-acylvinyl O-acyl isomers 8 were prepared and characterized. These vinylogous acyl compounds are able to isomerize in the same manner as simple O,N-diacylated 2-aminophenols 3 and 4, which under suitable conditions easily rearrange to give a dynamic equilibrium 3 ⇌ 4. Contrary to 3 and 4, however, the isomerization of 7 and 8 can be followed directly by spectroscopic methods, so that vinylogs of this type are useful model systems for studying acyl group migrations in 2-aminophenol. Kinetic measurements show that the mutual rearrangement of 7 and 8 is a reversible general based catalyzed reaction, being first order with respect to substrate and catalyst. The isomerization of the N-acetyl derivatives 7a-h as well as the N-benzoyl derivatives 7i-p results in strictly linear HAMMETT correlations with positive reaction constants ϱ. In the case of 7a-h the equilibrium constant K and the forward and reverse velocity constants k1 and k2 (including activation parameters) could be determined. The kinetic investigations and additional nonkinetic experiments indicate that the catalyst acts as proton acceptor and not  -  as hitherto supposed  -  as acyl group transferring nucleophile. Based on the findings an isomerization mechanism for mixed diacyl derivatives of 2-aminophenol is suggested.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 324 (1982), S. 1063-1068 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic Phosphorus Compounds. XIV. Studies on the Reactivity of Pesticidal Phosphoramidothioate Dimethyl Esters
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 55-65 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vinylogous Acyl Compounds. XX. Reactivity and Toxicity of Aryl-substituted β-Chlorovinyl Ketones, β-Chlorovinyl Aldehydes, and β-Chlorovinyl Methyleniminium SaltsBased on kinetic measurements, the nucleophilic replaceability of the chlorine in aromatic β-chlorovinyl ketones ArCO-CH = CH-Cl (1), isomeric β-chlorovinyl aldehydes OCH—CH=C(Cl)Ar(2), and corresponding β-chlorovinyl methyleniminium salts Me2N⊕;=CH—CH=C(Cl)Ar X⊖ (3) is compared and related to toxicological findings. The chemical reactivity of these important synthetic building blocks increases in the order 2〈1〈3, the acute toxicity (24 h LD50 i. p. in the mouse) shows the graduation 2〈3〈1. Compounds of type 1 prove to be relatively toxic (LD50 24-42 mg/kg) and display a marked necrotic action after percutaneous absorption, whereas the aldehydes 2 have not only a minor acute toxicity (LD50 158-298 mg/kg) but also a somewhat less marked skin damaging activity. In addition, the LD50 values of selected β-chlorovinyl carbonyl compounds are compared with those of corresponding halogen-free compounds as well as of vinylogous carbonamidium salts ArCO—CH=CH—N⊕R3X⊖. The latter, which can be used as synthetic equivalents of 1, differ in both the reduced acute toxicity and missing skin damaging properties.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...