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1983 (1)
1980 (1)
1978 (1)
1Author    Milan StrašákRequires cookie*
 Title    Substituent Effects in the Oxythallation of Alkenes  
 Abstract    The rate constants for oxythallation of alkenes have been correlated with their experi-mental and calculated ionization potentials respectively. A good correlation between the rate constants and the ionization potentials of alkenes was found. It was found that inductive effects were the most important in the oxythallation of RCH —CH2 and RiR2C = CH2 alkenes. From earlier studies [1, 2] it is obvious that the rate determining step of the oxidation of alkenes by thallic salts is the formation of the intermediate oxythallation adduct according to Eq (1): R2C=CR2 + T13+ + H20 -> [CR2(0H)CR2T1]2+ + H+ (1) 
  Reference    Z. Naturforsch. 33b, 224—227 (1978); received October 20 1977 
  Published    1978 
  Keywords    Alkenes, Oxythallation, Kinetics, Inductive Effect, Ionization Potentials 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-0224.pdf 
 Identifier    ZNB-1978-33b-0224 
 Volume    33 
2Author    D. Bryce-Smith, A. Gilbert, N. Al-Jalal, R. R. Deshpande, J. Grzonka, M. A. Hems, P. YianniRequires cookie*
 Title    Acid and Polarity Effects in Benzene Photoreactions with Alkenes and Alkynes  
 Abstract    The effects of polar solvents and proton donors on various photoreactions of the benzene ring with electron-acceptor alkenes and alkynes are described and discussed in relation to the various electronic excitation mechanisms involved. Proton donors prove valuable as mechanistic probes for polar intermediates in such processes, and can in some systems both initiate and divert reaction pathways. In 1970 we observed that the course of the photo-chemical cycloadditions of certain ethylenic and acetylenic compounds to benzene, earlier reported by us [1, 2], was profoundly altered in the presence of proton donors, leading to a type of photochemical Friedel-Crafts reaction [3]. Since then, we have described, mostly in preliminary form, numerous further examples of acid catalysis in the photo-reactions of benzene, viz. with amines [4], ethers [5], a ketone [6], a carboxylic acid [6], and hexa-fluorobenzene [7]. Our objective in this present paper is to bring together the previous preliminary reports on acid catalysis in the photoreactions of ethylenic and acetylenic compounds with benzene in conjunction with unpublished recent findings, and to provide a mechanistic rationale together with relevant experimental details. But before we proceed to consider the acid-cata-lysed processes, it is desirable to summarise the main types of reaction that have been shown to occur in the absence of acids. Ethylenes and/or acetylenes photoadd to benzene in the following four main ways: (a) ortho cycloaddition; (b) meto-cycloaddi-tion; (c) £>ara-cycloaddition; and (d) para-ene addi-tion [8, 9]. The mode of addition varies with the addend, and in some cases more than one pathway may be followed. In the case of (a), the adducts (1) of ethylenes may be obtained as such when the ethylenic addend is not a strong thermal dienophile, e.g. acrylonitrile [10], 2,3-dihydropyran [11]. When it is a strong dienophile, as in the case of maleic * Reprint requests to Prof. D. Bryce-Smith. 0340-5087/83/0900-1101/$ 01.00/0 anhydride and certain maleimides, a second mole-cule may add thermally to give the remarkably 
  Reference    Z. Naturforsch. 38b, 1101—1112 (1983); received May 2 1983 
  Published    1983 
  Keywords    Photoreactions, Benzene, Alkenes, Alkynes, Acid Effects 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-1101.pdf 
 Identifier    ZNB-1983-38b-1101 
 Volume    38 
3Author    J. Schmitzer, S. Gab, M. Bahadir, F. KörteRequires cookie*
 Title    Photomineralisierung chlorierter Alkane, Alkene und Aromaten an Kieselgel Photomineralization of Chlorinated Alkanes, Alkenes and Aromatics on Silica Gel  
 Abstract    The photodegradation to C02 (photomineralization) of chlorinated alkanes, alkenes and aromatics adsorbed on silica gel was examined. In addition to CO2, CI" and Cl2 were determined. The degradation depends considerably on the activity of the surface and decreases in the order alkenes > alkanes > aromatics. 
  Reference    Z. Naturforsch. 35b, 182—186 (1980); eingegangen am 6. September 1979 
  Published    1980 
  Keywords    Photomineralization, Degradation on Silica Gel, Chlorinated Alkanes, Alkenes, Aromatics 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-0182.pdf 
 Identifier    ZNB-1980-35b-0182 
 Volume    35