No abstract

ROBIY A. COX and KEITH YATES. Can. J. Chem. 57,2944Chem. 57, (1979 Kinetic equations, applicable to A-1, A-S,2, and A-2 reactions in concentrated aqueous acids, are derived. The variation in reaction rate with varying acid concentration is treated in terms of the "excess acidity" of the medium (X-function), rather than in terms of Hammetttype acidity functions or the water activity. The parameters obtained are the medium-independent rate constant k,, in the aqueous standard state, as an intercept, and a slope parameter 1~1 ' ; hydration parameters (r-values) are also obtained, for A-2 reactions. The equations derived are shown to apply to A-1 acetal hydrolyses, A-SE2 electrophilic aromatic substitutions, and mixed A-21A-I ester hydrolyses. In a general discussion of available methods for analyzing rate data in these media, it is shown that the X-function method encompasses most, if not all, of the others, and that classical acidity functions are no longer necessary. Dans une discussion genirale sur l'ensemble des methodes disponibles d'analyse de donnees de vitesse en milieu acide on a montre que la methode de la fonction de X englobe la plupart si ce n'est pas toutes les autres methodes, et que les fonctions classiques d'acidite ne sont plus nkcessaires.[Traduit par le journal]

Oxford University Press, 2013. 160 pp., softcover, $ 45.00.—ISBN 978‐0199670529

Oxford University Press, 2013. 160 S., Broschur, 45.00 $.—ISBN 978‐0199670529

systems where IO2 may be involved including erythropoietic protoporphyrias2 and hematoporphyrin p h~t o c h e m o t h e r a p y .~~-~~ The relatively precise distance and angle information for 4-7 provided by N M R studies coupled with the triplet energy transfer rate constants determined by flash photolysis provide correlations among structural, dynamical, and photophysical paratneters which will be useful in developing or testing quantitative theories of energy transfer between chromophores within a single molecule.For example, it appears that a quantum mechanical calculation of orbital overlap would be necessary in order to correlate the above-mentioned electron transfer in polystyrene with structure. These molecular systems are also potentially useful for studying intramolecular electron transfer reactions; in fact, a carotenoporphyrin linked to a quinone has recently been found to form a long-lived charge-separated state upon excitation with visible light.56 (52) Mathews-Roth, M. M. -(4-hydroxyphenyl)-lO,l5,20-tris(4methylphenyl)porphyrin, 57412-08-5; 7'-apo-7'-(4-(iodomethyl)phenyl)-P-carotene, 95998-89-3; 5-(3-hydroxyphenyl)-lO,l5,20-tris(4methylphenyl)porphyrin, 57412-06-3; 5-(2-hydroxyphenyl)-lO,l5,20tris(4-methylphenyl)porphyrin, 57412-07-4; 5-(4-(3-hydroxypropoxylphenyl)-10,15,20-tris(4-methylphenyl)porphyrin, 95998-90-6; abromo-p-toluoyl chloride, 52780-16-2; 2,3-dimethoxybenzaldehyde, 86-51-1; p-tolualdehyde, 104-87-0; pyrrole, 109-97-7; propionic acid, 79-09-4; 2,6-dimethoxybenzaldehyde, 3392-97-0; ethylene oxide, 75-21-8; methyl a-bromo-p-toluate, 2417-72-3; P-apo-S'-carotenal, 1 107-26-2; oxygen, 7782-44-7. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ (56) Moore, T. A.; Gust, D.; Mathis, P.; Mialocq, J. C.; Chachaty, C.; Bensasson, R. V.; Land, E. J.; Doizi, D.; Liddell, P. A.; Lehman, W. R.; Nemeth, G. A.; Moore, A. L. Nature (London) 1984, 307, 630-632.Abstract: The condensation of acetaldehyde (1) to an equilibrium mixture of aldol ( 2 ) and crotonaldehyde (3) is second order in 1. An excess acidity analysis reveals that a water molecule is also involved in the rate-limiting step; the reaction is actually the base-assisted addition of vinyl alcohol to protonated 1, even in concentrated H2S04. A previous report of a kinetically first-order conversion of 1 to 3 is shown to be due to the presence of a fast-reacting oligomer of 1. The reaction of 1 in D2S04 leads to partially deuterated 3, a result ascribed to partial conversion of vinyl alcohol to deuterated 1. Hydrogen isotope exchange of 3 was also observed, but at a slower rate. The rates of enolization of 1 were studied by iodination and are consistent with previous results and the proposed mechanism. The interconversion of 2 and 3 is shown to proceed via the enol of 2; in this case the rate-limiting step is water attack on/water loss from protonated 3/2, not proton transfer at carbon.The acid-catalyzed condensation of acetaldehyde (1) to aldol