Browsing by Author "Crooks, John E."

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    Kinetics and Thermodynamics of Hydrogen-bond Formation and Proton-transfer in the Reactions of Tetrabromo phenolphthalein Ethyl Ester with Amine Bases in Chlorobenzene, by a Microwave Temperature-jump Method
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (6), 1973) Caldin, Edward F.; Crooks, John E.; Donnell, Derek O’
    The proton-transfer reactions of the substituted phenol tetrabromophenolphthalein ethyl ester with various aliphatic and aromatic amines in chlorobenzene have been studied over ranges of temperature. Equilibrium constants and thermodynamic parameters have been determined spectro- photometrically; rate constants and activation parameters for the forward and back reactions have been determined with the aid of a microwave temperature-jump apparatus. As in the case of the reactions with 2,4-dinitrophenol (preceding paper), the forward rate constants approach the value for diffusion control, and are not correlated with the equilibrium constants but appear to reflect steric factors. With some of the amines, spectrophotometric investigation revealed the presence also of a hydrogen-bonded species, whose formation may precede the proton-transfer step; equi librium constants were determined for several of these complexes. The kinetics have been analysed on the basis of a two-stage mechanism, hydrogen-bond formation followed by proton-transfer. Various considerations, including the absence of a Bronsted-type relation between rate and equilibrium constants, indicate that the formation of a hydrogen-bonded complex or an encounter-complex is rate-limiting and the proton-transfer relatively fast.
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    Kinetics and Thermodynamics of the Proton-transfer Reactions of 2,4-Dinitrophenol with some Amine Bases in Chlorobenzene studied by a Microwave Temperature-jump Method
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (6), 1973) Caldin, Edward F.; Crooks, John E.; Donnell, Derek O’
    The proton-transfer reactions of 2,4-dinitrophenol with trimethylamine, tri-n-octylamine, quinuclidine and triethylenediamine in chlorobenzene at 25CC have been studied. Equilibrium constants have been determined spectrophotometrically, and rate constants for some of the reactions have been determined by means of a microwave temperature-jump apparatus. The forward rate constants are one-tenth to one-hundredth of the value calculated for diffusion control. They do not correlate with the equilibrium constants, but appear to be related to steric factors.