An Examination of the Heat Capacity of Activation for the Hydrolysis of t-Butyl Chloride in Water

1972 ◽  
Vol 50 (2) ◽  
pp. 167-175 ◽  
Author(s):  
J. M. W. Scott ◽  
R. E. Robertson
Keyword(s):  
Heat Capacity ◽  
Alternative Hypothesis ◽  
Ion Pairs ◽  
Heat Capacities ◽  
Butyl Chloride ◽  
Methyl Halides ◽  
Displacement Reactions ◽  
Arrhenius Temperature Dependence ◽  
Hydrolysis Of ◽  
Arrhenius Temperature

The influence of ion-pair intermediates on solvolytic displacement reactions is considered for cases where the observed rate constant is complex.Such complex and composite rate constants under certain conditions may show deviations from the Arrhenius temperature dependence law. The deviations will manifest themselves as "spurious" positive and/or negative heat capacities of activation, superimposed on the real heat capacity terms.The hypothesis of Albery and Robinson (1) which proposes that the heat capacity of activation for t-butyl chloride is entirely "spurious" in the sense outlined above, is critically evaluated and rejected. An alternative hypothesis that considers the heat capacity to be a manifestation of solvation effects is retained.The mechanism of the hydrolysis of both the methyl and t-butyl halides in water is discussed and the kinetic laws appropriate to each are shown to be consistent with real heat capacities of activation. The mechanism proposed differs from the classical SN1–SN2 description. Both series of substrates are considered to give rise to intimate-ion-pairs but in the case of the methyl halides these react further by a path which involves the nucleophilicity of the solvent in a kinetically significant way. In the cases of the tertiary compounds, solvent separation of ion-pairs becomes kinetically significant. The nucleophilic component which characterizes the destruction of the solvent-separated ion-pairs for the tertiary compounds is kinetically insignificant.

The Hydrolysis of t-Butyl Chloride in Aquo-Organic Mixtures: Heat Capacity of Activation and Solvent Structure

1972 ◽  
Vol 50 (9) ◽  
pp. 1353-1360 ◽  
Author(s):  
R. E. Robertson ◽  
S. E. Sugamori
Keyword(s):  
Heat Capacity ◽  
Temperature Dependence ◽  
High Water ◽  
Remarkable Difference ◽  
Solvent Structure ◽  
Butyl Chloride ◽  
Organic Mixtures ◽  
A Value ◽  
Polar Solutes ◽  
Hydrolysis Of

The temperature dependence of the rate of solvolysis of t-butyl chloride in mixtures of tetrahydrofuran and of acetonitrile in water have been determined. In the high-water range both minor co-solvents lead to a reduction in the value of ΔH≠ similar to that found previously where alcohol was the co-solvent. However, a remarkable difference in the values of [Formula: see text] across the same concentration range reflected a difference in the effect of these two co-solvents on the structural properties of the several solvent media. Where tetrahydrofuran or alcohols are the minor co-solvent, [Formula: see text] becomes much more negative until that concentration is reached where the quasi-aqueous structure collapses. Where acetonitrile is the minor co-solvent [Formula: see text] becomes more positive relative to the value found for hydrolysis in water until a value of about −40 cal deg−1 mol−1 is reached. The implication of these findings concerning the nature of solvation of weakly polar solutes in such mixtures is discussed.

Ion pairs and heat capacity of activation for 2,2-disubstituted cyclopropyl bromides

1976 ◽  
Vol 54 (8) ◽  
pp. 1246-1252 ◽  
Author(s):  
Surendra Singh ◽  
Ross Elmore Robertson
Keyword(s):  
Heat Capacity ◽  
Transition State ◽  
Relative Rate ◽  
Ion Pairs ◽  
Water Structure ◽  
Ion Pair ◽  
External Effects ◽  
Enthalpy Of Activation ◽  
Rate Ratios ◽  
Hydrolysis Of

The temperature dependence of the rates of hydrolysis of 2,2-dimethylcyclopropyl bromide, 2,2-cis-vinyl-trans-methylcyclopropyl bromide and 2,2-cis-methyl-trans-vinylcyclopropyl bromide have been determined in water. The temperature coefficient of the enthalpy of activation (ΔCp≠) for these compounds was determined to be −52, −27 and −37 cal deg−1 mol−1 respectively. The relative rate ratios for hydrolysis of the 2,2-methylvinylcyclopropyl bromides with respect to the appropriate 2-vinylcyclopropyl bromide isomer indicate a considerable progress towards allyl cations at the transition state in contrast to the indications of the ΔCp≠ values.The ΔCp≠ term for such reactions in water depends to an important degree on the external effects of charge development on water structure but is insensitive to internal electrostatic effects. In the three examples of ΔCp≠ reported in this study, all tend to show small external effects in spite of evidence which might suggest larger. The differences in ΔCp≠ are attributed to the particular shape and charge distribution of the quasi-ion pair.

Heat capacities and enthalpies of fusion and transformation for solvates of some salts with dimethyl sulfoxide and dimethylformamide

1988 ◽  
Vol 53 (12) ◽  
pp. 3072-3079
Author(s):  
Mojmír Skokánek ◽  
Ivo Sláma
Keyword(s):  
Heat Capacity ◽  
Phase Transformation ◽  
Phase Transformations ◽  
Dimethyl Sulfoxide ◽  
Liquidus Temperature ◽  
Molar Heat Capacity ◽  
Solid Phase ◽  
Zinc Nitrate ◽  
Heat Capacities ◽  
Liquid Phases

Molar heat capacities and molar enthalpies of fusion of the solvates Zn(NO3)2 . 2·24 DMSO, Zn(NO3)2 . 8·11 DMSO, Zn(NO3)2 . 6 DMSO, NaNO3 . 2·85 DMSO, and AgNO3 . DMF, where DMSO is dimethyl sulfoxide and DMF is dimethylformamide, have been determined over the temperature range 240 to 400 K. Endothermic peaks found for the zinc nitrate solvates below the liquidus temperature have been ascribed to solid phase transformations. The molar enthalpies of the solid phase transformations are close to 5 kJ mol-1 for all zinc nitrate solvates investigated. The dependence of the molar heat capacity on the temperature outside the phase transformation region can be described by a linear equation for both the solid and liquid phases.

Heat capacity of activation for the hydrolysis of methanesulfonyl chloride and benzenesulfonyl chloride in light and heavy water

1969 ◽  
Vol 47 (22) ◽  
pp. 4199-4206 ◽  
Author(s):  
R. E. Robertson ◽  
B. Rossall ◽  
S. E. Sugamori ◽  
L. Treindl
Keyword(s):  
Heat Capacity ◽  
Free Energy ◽  
Temperature Dependence ◽  
Heavy Water ◽  
Bond Formation ◽  
Sulfonyl Chlorides ◽  
Benzenesulfonyl Chloride ◽  
Methanesulfonyl Chloride ◽  
Hydrolysis Of ◽  
Parameter Temperature Dependence

Rates of solvolysis of methanesulfonyl chloride and benzenesulfonyl chloride have been determined in H2O and D2O. The free energy, enthalpy, entropy, and heat capacity of activation were calculated. The exceptional accuracy of the data permitted an estimation of dΔCp≠/dT from a four parameter temperature dependence of the kinetic rates.From these data we conclude that both sulfonyl chlorides hydrolyse by the same mechanism (Sn2) The change in R from CH3 to C6H5 in RSO2Cl did not alter ΔCp≠ but ΔS≠ (20°) was changed from −8.32 to −13.25 cal deg−1 mole−1, respectively. The significance of this difference is attributed to the probability of bond formation rather than to differences in solvent reorganization.

Self-diffusion of Ag+ and Na+ in molten Ca(NO3)2-KNO3

1972 ◽  
Vol 25 (8) ◽  
pp. 1613 ◽  
Author(s):  
BJ Welch ◽  
CA Angell
Keyword(s):  
Electrical Conductance ◽  
Ionic Species ◽  
Tracer Diffusion ◽  
Dilute Solution ◽  
Self Diffusion ◽  
Capillary Method ◽  
Arrhenius Temperature Dependence ◽  
Radio Tracer ◽  
Tracer Diffusion Coefficients ◽  
Arrhenius Temperature

In order to explore the behaviour of diffusing ionic species in a molten salt in which non-Arrhenius behaviour of other transport properties is established, the diffusivities in dilute solution of Ag+ and Na+ in 38.1 mol% Ca(NO3)2+ 61.9 mol% KNO3 have been measured. For both ions limited radio-tracer diffusion coefficients, determined using a diffusion-out-of-capillary method, are reported. D(Ag+) has also been measured by chronopotentiometry, by which means the range and reliability of the measurements were considerably extended. Chronopotentiometric and tracer data agree within expected errors of measurement. Both ionic diffusivities show a non-Arrhenius temperature dependence which is indistinguishable in magnitude from that of the electrical conductance of the solvent melt.

Heat capacities at constant volume, free volumes, and rotational freedom in some liquids

1971 ◽  
Vol 24 (9) ◽  
pp. 1817 ◽  
Author(s):  
DD Deshpande ◽  
LG Bhatgadde
Keyword(s):  
Heat Capacity ◽  
Free Volume ◽  
Heat Capacities ◽  
Organic Liquids ◽  
Velocity Of Sound ◽  
Velocity Data ◽  
Volume Analysis ◽  
Straight Lines ◽  
Rotational Freedom ◽  
Residual Heat

This paper presents the experimental results on the velocity of sound, densities, and heat capacities of eight organic liquids at 25�, 35�, and 45�C. Using Eyring's equation, the free volumes have been calculated from the sound velocity data. For pure liquids, a quantity Cv* = (Cv)L- (Cv)g- Cstr called the residual heat capacity is found to be linearly dependent on free volume. Analysis of the data for 34 liquids shows that a plot of residual heat capacity against the free volume gives a series of straight lines differing in slopes for different groups of liquids such as hydrocarbons, halogen-substituted hydrocarbons, alcohols, etc. This behaviour is ascribed as being due to different degrees of rotational freedom of molecules in these liquids.

scholarly journals DC conductivity of polyethylene and crosslinked polyethylene measured with a dynamic temperature program

2017 ◽  
Author(s):  
Hossein Ghorbani ◽  
Carl-Olof Olsson ◽  
Marc Jeroense
Keyword(s):  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Thermal Conditions ◽  
Dc Conductivity ◽  
Protective Film ◽  
Dynamic Temperature ◽  
Operation Conditions ◽  
Heating And Cooling ◽  
Arrhenius Temperature Dependence ◽  
Arrhenius Temperature

<p>Electrical conductivity of HVDC cable insulation materials is important for its function. It is very practical to evaluate this parameter by DC conductivity measurements on press molded polymeric plates samples. While in real operation conditions, the insulation undergoes both static and dynamic thermal conditions, most of the published research in this area is still focused only on steady state thermal conditions. In this work, the focus is instead on the behavior of electrical conductivity under dynamic thermal conditions. Press molded XLPE and LDPE plate samples with different preparations are tested under 25 kV/mm DC field with a dynamic temperature profile ranging from room temperature to 90 °C.<br />It was discovered that in many cases, the measured conductivity during dynamic measurements strongly deviates from the expected Arrhenius temperature dependence; instead the conductivity shows a nonmonotonic<br />temperature dependence manifested as conductivity peaks during heating and cooling. The behavior is found to be strongly related to the type of protective film used during press molding of the sample; further degassing leads to a reduction of the nonmonotonic temperature dependence and with long<br />degassing the behavior tends to the expected Arrhenius temperature dependence.</p>

scholarly journals The stereochemical course of reactions catalysed by the cellobiohydrolases produced by Talaromyces emersonii

1992 ◽  
Vol 283 (1) ◽  
pp. 31-34 ◽  
Author(s):  
M M Brooks ◽  
M G Tuohy ◽  
A V Savage ◽  
M Claeyssens ◽  
M P Coughlan
Keyword(s):  
Degradation Product ◽  
Proteolytic Degradation ◽  
Substrate Specificities ◽  
Talaromyces Emersonii ◽  
Anomeric Configuration ◽  
Culture Filtrates ◽  
Apparent Homogeneity ◽  
Displacement Reactions ◽  
Hydrolysis Of

Three forms of exocellobiohydrolase (EC 3.2.1.91), CBH IA, CBH IB and CBH II, were isolated to apparent homogeneity from culture filtrates of the aerobic fungus Talaromyces emersonii. CBH IA and CBH II appear to be native forms of these enzymes, while CBH IB may represent a proteolytic degradation product of the CBH IA enzyme. The hydrolysis of beta-cellobiosyl fluoride by each form was monitored by 1H-n.m.r. spectroscopy. The reactions catalysed by CBH IA and CBH IB proceed with retention of the anomeric configuration, whereas that catalysed by CBH II is one of inversion. Thus one may deduce that CBH IA (or CBH IB) and CBH II operate double and single displacement reactions respectively during catalysis of substrate. On the basis of these findings and the observed substrate specificities of the various forms, one may conclude that CBH IA (and CBH IB) is a family C enzyme, while CBH II belongs to family B [Henrissat, Claeyssens, Tomme, Lemesle & Mornon (1989) Gene 81, 83-95].

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