Journal Archive Collections

Permanent URI for this communityhttp://localhost:4000/handle/123456789/16937

Browse

Author: search.filters.author.Caldin, Edward F.

Search Results

Now showing 1 - 7 of 7
  • No Thumbnail Available
    Item
    Kinetic Isotope Effect in the Reaction of 4-Nitrophenylnitromethane with the Cyclic Amidine Base DBU [l,5-diazabicyclo(5,4,0)undec-5-ene]
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (08), 1978) Caldin, Edward F.; Rogne, Otto
    Kinetic deuterium isotope effects have been determined for the reaction of the cyclic amidine base DBU [1,5-diazabicyclo(5,4,0)undec-5-ene] with the carbon acid 4-nitrophenylnitromethane in toluene solution from –5 to +25°C. The isotopic rate ratio for the forward reaction (kHf/kDf) at 25°C is 13.3 ± 1.2; this is large enough to suggest an appreciable tunnelling correction. The activation enthalpies are strikingly low, both for proton and deuteron transfer: ΔH‡Hf= 2.0 ± 0.2 kcal mol–1(8.4 ± 0.8 kJ mol–1) and ΔH‡Df= 3.6 ± 0.3 kcal mol–1(15.1 ± 1.3 kJ mol–1). The interpretation of these results is discussed.
  • No Thumbnail Available
    Item
    Kinetics of the Reaction Between 2,4-Dinitrophenol and Tri-n-octylamine in Chlorobenzene Solution Diffusion and other Rate-limiting Factors
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Caldin, Edward F.; Tortschanoff, Karl
    The kinetics of the reaction between 2,4-dinitrophenol and tri-n-octylamine in chlorobenzene solution have been investigated by a microwave temperature-jump technique. The rate constant is about 30 times smaller than the value calculated from the Smoluchowski treatment for a diffusion-controlled reaction. The activation enthalpy is slightly negative (ΔH[graphic omitted]=–6.7 ± 2 kJ mol–1 or –1.6 ± 0.5 kcal mol–1). This is strong evidence against a one-step mechanism. A three-step mechanism accommodates the results. For this mechanism the significant fact about ΔH[graphic omitted] is that it is lower than the viscosity-controlled value, rather than the fact that it is negative.
  • No Thumbnail Available
    Item
    Kinetic Isotope Effects in the Reactions of 4-Nitrophenylnitromethane with Alkylamidine Bases in Toluene
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Caldin, Edward F.; Rogne, Otto; Wilson, Christopher J.
    Kinetic isotope effects have been determined for the proton-transfer and deuteron-transfer reactions of 4-nitrophenylnitromethane (4-NPNM; NO2C6H4CH2NO2, NO2C6H4CD2NO2) with two alkylamidine bases [HN = C(NEt2)R; R = n-butyl, n-nonyl] in toluene solution. The observed values of the isotopic rate ratio kHf/kDf at 25°C are 11.7 ± 1.0 and 8.0 ± 0.3, respectively. The former value indicates an appreciable tunnel correction; this is confirmed by a value of (ΔH[graphic omitted]D-ΔH[graphic omitted]H)= 2.5 ± 0.8 kcal mol–1(10 ± 3 kJ mol–1). The isotopic differences are not precise enough to allow calculations of the dimensions of the energy barrier.
  • No Thumbnail Available
    Item
    Kinetics of the reaction of the nickel(II) ion with pyridine-2-azo-p-dimethylaniline in t-butanol + water mixtures
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (12), 1974) Caldin, Edward F.; Godfrey, Peter
    Rate constants and activation parameters have been determined for the reaction of the nickel(II) ion with pyridine -2-azo-p-dimethylaniline, in a series of t-butanol + water mixtures with mole fractions from 0 to 0.4 t-butanol. The rate constant at 25°C varies little with composition, but the enthalpy and entropy of activation both vary considerably, with compensation; they show maxima and minima, which are discussed in relation to theories of solvent structure.
  • No Thumbnail Available
    Item
    Solvent Effects in the Kinetics of Fast Proton-transfer Reactions: Diffusion, Preliminary Complexes, and Steric Factors
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Burfoot, Graham D.; Caldin, Edward F.; Goodman, Howard
    The kinetics of the reaction of tri-n-butylamine with the substituted phenol tetrabromophenol- phthalcin ethyl ester (Bromophthalein Magenta E) in various solvents have been investigated, by a microwave temperature-jump method. The rate constants are inversely correlated with the viscos ities of the solvents, and are 15 to 30 times less than the values calculated for diffusion control. Bromophthalein Magenta E shows close similarities with other substituted phenols (c.g. 2,4-dinitro- phenol and Bromophcnol Blue) in its reactions with tertiary aliphatic amines. All the data on these reactions are satisfactorily correlated by a theory which envisages diffusion-controlled formation of weakly-bound complexes, during whose life-time the reactant molecules can rotate into positions where the active centres are adjacent so that reaction can proceed. Alternative models are con sidered and found unsatisfactory.
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    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.