- Alkaline hydrolysis of Y-substituted phenyl phenyl thionocarbonates: Effect of changing electrophilic center from C=O to C=S on reactivity and mechanism
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Second-order rate constants (kOH-) have been measured spectrophotometrically for reactions of Y-substituted phenyl phenyl thionocarbonates (4a-i) with OH- in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The ksu
- Kim, Song-I,Park, Hey-Ran,Um, Ik-Hwan
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scheme or table
p. 179 - 182
(2011/10/31)
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- Effect of the leaving group solvation on solvolytic behavior of benzhydryl derivatives
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An effect of the leaving group (LG) solvation on reactivity of benzhydryl derivatives in SN1 reactions has been investigated by using X, Y-substituted benzhydryl phenyl carbonates, methyl carbonates, 3, 5-dinitrobenzoates (DNB), and the corresponding benzhydryl chlorides as reference compounds. Reaction constants (sf) derived from LFER equation log k (25°C)=sf (Nf+Ef) indicate that s f parameters of carbonates and DNBs decrease as the fraction of the water in a given solvent/water mixture increases, while those of chlorides remain unchanged. This phenomenon is due to less important solvation and less charge separation in the TS. Effects of the solvents on the reaction rates were analyzed by Grunwald-Winstein correlations using various solvent-ionizing power scales. The m values obtained for carbonates and DNBs are considerably smaller than the m values for chlorides. Also, the solvolysis rate constants of substrates that have stronger electrofuges are less influenced by solvent (lower m) than those with weaker electrofuges. Values of m parameters obtained for a given substrate in a given binary solvent system correlate well with the electrofugality of the generated benzhydrylium ion. Abscissa at which m=0 represents the extrapolated critical electrofugality Ecrit f of the substrates whose solvolysis rates should not depend on the water fraction in the aqueous/organic solvent mixtures. Similar values for the critical electrofugality have also been obtained from extrapolated logk versus Ef plots. Copyright
- Denegri, Bernard,Kronjaa, Olga
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experimental part
p. 495 - 503
(2010/04/30)
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- Carbon kinetic isotope effects on the hydrolysis of aryl carbonates
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Carbon kinetic isotope effects on the hydrolysis of aryl carbonates in 1:1 (v/v) dioxane-water at 25 °C at various pHs were used to calculate isotope effects on the reactions with hydroxide ion and with water. For diphenyl carbonate kOH12/kOH13 = 1.0482 and kw12/kw13 = 1.0509. For bis(p-methoxyphenyl)carbonate kOH12/kOH13= 1.0493 and kw12/kw13 = 1.0518. For bis(p-nitrophenyl)carbonate kOH12/KOH13 = 1.0476. The small change in the isotope effect with substituent group for both alkaline and neutral hydrolysis is in contrast to the large substituent effect on the rate constants for both reactions. The nearly constant isotope effect indicates that transition-state structures arc similar for all substrates.
- Marlier, John F.,O'Leary, Marion H.
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p. 5996 - 5998
(2007/10/02)
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- Carbamates of homolysergols (8β-hydrohyethylergolines) and compositions thereof
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Novel ergoline derivatives are disclosed having the general formula (I) STR1 wherein R1 is hydrogen, and alkyl radical (C1 to C4) either straight of branched chain, Z is hydrogen, bromine, S-RIV (in which R
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