QUADRUPOLE RELAXATION FOR A SPIN I = 3/2: THE F19 N.M.R. SPECTRA OF BF3 AND ClO3F

1963 ◽  
Vol 41 (12) ◽  
pp. 3063-3069 ◽  
Author(s):  
J. Bacon ◽  
R. J. Gillespie ◽  
J. W. Quail
Keyword(s):  
Electric Quadrupole ◽  
Activation Energies ◽  
Kcal Mole ◽  
Molecular Reorientation ◽  
Quadrupole Relaxation

An expression is derived for the broadening of the components of the quartet obtained for the n.m.r. spectrum of nuclei coupled to a nucleus of spin 3/2 undergoing electric quadrupole relaxation. It is shown that the F19 spectra of BF3 and ClO3F at various temperatures may be satisfactorily interpreted by means of this expression. Activation energies for molecular reorientation of 1.4 kcal/mole for BF3 and 1.0 kcal/mole for ClO3F are obtained.

Tracer Impurity Diffusion in Liquid Metals: K in Na and Na in K

1973 ◽  
Vol 28 (1) ◽  
pp. 117-119
Author(s):  
T. Persson ◽  
S. J. Larsson
Keyword(s):  
Liquid Metals ◽  
Activation Energies ◽  
Impurity Diffusion ◽  
Effective Activation ◽  
Kcal Mole ◽  
Self Diffusion

The diffusivities of 42K in Na and of 24Na in K have been measured between 100 ° and 285 °C, utilizing an „infinite capillary" technique. The results are adequately described by the Arrhenius relations (in cm2/s) DK in Na = 0.46 · 10-3 exp (-1.82/RT) and DNa in K = 0.93 · 10-3 exp (-2.11/RT). The differences ΔQ in effective activation energies between impurity diffusion and self-diffusion are about -0.4 kcal/mole for Na and +0.1 kcal/mole for K. This can be satisfactorily explained by electrostatic screening arguments. The impurity diffuses slower than the host atoms in Na, faster in K.

The Rate of Racemization and Isomerization of the cis-Chloroaquobis(ethylenediamine) cobalt(III) Ion

1963 ◽  
Vol 16 (3) ◽  
pp. 352 ◽  
Author(s):  
AM Sargeson
Keyword(s):  
Trans Isomer ◽  
Activation Energies ◽  
Kcal Mole

The rate of isomerization of the cis-chloroaquobis(ethylenediamine)cobalt(III) ion to the trans-isomer k30� = 2.7 x 10-3 min-1 has been shown to be the same as the rate of racemization k30� = 2.61 x 10-3 min-1. The activation energies and entropies for the reactions are AEa = 27 � 1 kcal/mole, AS? = $2 e.u., and ΔEa = 26.7 � 0.2 kcal/mole, AS? = +2.3 e.u. respectively.

THE REACTIONS OF TRIFLUOROMETHYL RADICALS WITH PROPANE, n-BUTANE, AND ISOBUTANE

1956 ◽  
Vol 34 (2) ◽  
pp. 103-107 ◽  
Author(s):  
P. B. Ayscough ◽  
E. W. R. Steacie
Keyword(s):  
Rate Constants ◽  
Hydrogen Abstraction ◽  
Activation Energies ◽  
Methyl Radicals ◽  
Kcal Mole

A study of the reactions of trifluoromethyl radicals, produced by the photolysis of hexafluoroacetone, with propane, n-butane, and isobutane has been made. The rate constants of the hydrogen-abstraction reactions have been determined at temperatures between 27 °C and 119 °C and the activation energies found to be 6.5 ± 0.5, 5.1 ± 0.3, and 4.7 ± 0.3 kcal./mole respectively. These values are compared with those obtained for the reactions with methane and ethane, and with the corresponding reactions of methyl radicals.

MOLECULAR REORIENTATION IN FERROELECTRIC LITHIUM HYDRAZINIUM SULPHATE

1967 ◽  
Vol 45 (10) ◽  
pp. 3257-3263 ◽  
Author(s):  
W. D. MacClement ◽  
M. Pintar ◽  
H. E. Petch
Keyword(s):  
Low Temperatures ◽  
Room Temperature ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Resonance Absorption ◽  
Spin Lattice Relaxation ◽  
Kcal Mole ◽  
Molecular Reorientation ◽  
Hindered Rotation ◽  
Spin Lattice

The temperature dependence of the spin-lattice relaxation time T1 and of the second moment of the magnetic-resonance absorption signal has been determined for protons in powdered lithium hydrazinium sulphate over the range 80–480 °K. These measurements indicate that the hydrazinium ion is rigid only at very low temperatures. As the temperature is raised, the −NH3 group begins to undergo hindered rotation about the N–N axis with an activation energy of 4.2 kcal/mole and the effect of this motion on the line width becomes pronounced in the region of 85 °K. Further molecular reorientation begins above room temperature and is probably reorientation of the −NH2 group about either the N–N axis or the bisectrix of the H–N–H angle. Above 435 °K the hydrazinium ion begins to tumble about several axes and at 480 °K diffuses through the structure.

scholarly journals Allyl radicals from 3,3′-azo-1-propene

1970 ◽  
Vol 48 (17) ◽  
pp. 2745-2754 ◽  
Author(s):  
Basil H. Al-Sader ◽  
Robert J. Crawford
Keyword(s):  
Activation Energies ◽  
Major Product ◽  
Bond Dissociation Energies ◽  
Kcal Mole ◽  
Allyl Radical ◽  
First Order ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
First Order Kinetics

3,3′-Azo-1-propene (4), 3,3′-azo-1-propene-3,3′-d2 (5) and 3,3′-azo-1-propene-3,3,3′3′-d4 (6) have been synthesized and characterized. Thermolysis of 4, at 40–300 Torr, and in the region 150–170°, followed first order kinetics (Ea = 36.1 ± 0.2 kcal mole−1, log A = 15.54 ± 0.10) the major product, >99.9%, being 1,5-hexadiene (9). The presence of less than 0.1% propene suggests that the allyl radical is unable to abstract hydrogen from 4 or 9. Statistical scrambling of deuterium, in the products of thermolysis of 5 and 6, was observed. These results are interpreted in terms of a mechanism wherein allyl radicals are generated. Comparison of the activation energies for azoalkanes and 4 with the bond dissociation energies of hydrocarbons suggest that a good Polanyi plot is possible.

THE REACTIONS OF PERFLUOROETHYL RADICALS WITH HYDROGEN AND METHANE

1960 ◽  
Vol 38 (11) ◽  
pp. 2128-2135 ◽  
Author(s):  
S. J. W. Price ◽  
K. O. Kutschke
Keyword(s):  
Activation Energy ◽  
Hydrogen Abstraction ◽  
Frequency Factor ◽  
Activation Energies ◽  
Recombination Reaction ◽  
Limited Data ◽  
Kcal Mole ◽  
Fluorinated Radical

The reactions of C2F5 radicals, produced by the photolysis of (C2F5)2CO, with methane and hydrogen have been studied. Assuming zero activation energy for 2C2F5 → C4F10 the activation energies for C2F5 + CH4 → C2F5H + CH3 and C2F5 + H2 → C2F5H + H are 10.6 kcal/mole and 11.9 kcal/mole respectively. The present results have been correlated with data on the reactions of CF3, C3F7, and CH3 radicals with H2, D2, CH4, and C2H6. Taking Erecombination ≈ 0 in all cases and assuming the frequency factor for the recombination reaction varies little from radical to radical, the order of ease of hydrogen abstraction from a given substrate is CF3 > C2F5 > C3F7 > CH3. Similarly the ease of hydrogen abstraction from a substrate by a given fluorinated radical is C2H6 > H2 > CH4 > D2. A calculation based on very limited data indicates the reaction CH3 + C2F5COC2F5 → CH3COC2F5 + C2F5 may occur with an activation energy of approximately 7 kcal/mole.

The decomposition of silver azide

1958 ◽  
Vol 246 (1245) ◽  
pp. 206-216 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Polycrystalline Material ◽  
Silver Ions ◽  
Activation Energies ◽  
Dielectric Constants ◽  
Kcal Mole ◽  
Silver Azide ◽  
Thermo Electric ◽  
Temperature Form ◽  
Electronic Conductance

The thermal decomposition of both allotropic forms of silver azide as polycrystalline material and as single crystals has been investigated. The activation energies are 44 to 46 kcal/mole (low-temperature form) and 31 to 32 kcal/mole (high-temperature form). The spectra of freshly prepared and of partially decomposed crystals have been examined and various colour centres tentatively identified. Measurements of the ionic and electronic conductance of unsintered and sintered polycrystalline material together with those of thermo-electric power lead to the conclusion that the charge carriers are interstitial silver ions and electrons. From results of the photoconductance response at various wavelengths, the width of the zone for intrinsic conductance in pure silver azide has been evaluated, and also the optical activation energies in partially decomposed salt for electron excitation from colloidal centres to the conduction band for both allotropes. The temperature coefficients of electronic conductance in partially decomposed material in the quenched and in the annealed state have also been measured, and allow an evaluation of the corresponding thermal activation energies, and hence of the ratios of the static and high-frequency dielectric constants. A possible rate-determining step in the thermal decomposition has, in consequence, been suggested and a tentative theory of the subsequent processes proposed.

THE VAPOR PHASE PHOTOLYSIS OF HEXAFLUOROACETONE IN THE PRESENCE OF METHANE AND ETHANE

1955 ◽  
Vol 33 (5) ◽  
pp. 743-749 ◽  
Author(s):  
P. B. Ayscough ◽  
J. C. Polanyi ◽  
E. W. R. Steacie
Keyword(s):  
Activation Energy ◽  
Vapor Phase ◽  
Activation Energies ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Photolytic Decomposition

The photolytic decomposition of hexafluoroacetone by light of wavelength 3130 Å has been used to produce trifluoromethyl radicals for a study of their reactions with methane and ethane. It has been shown that these radicals abstract hydrogen with greater facility than do methyl radicals. The activation energies for the two reactions[Formula: see text]and[Formula: see text]are found to be 10.3 ± 0.5 kcal./mole and 7.5 ±0.5 kcal./mole respectively, if one can assume zero activation energy for the recombination of trifluoromethyl radicals.

Solid State Formation of Superconducting Phases in the T1-Ca-Ba-Cu-O System

1989 ◽  
Vol 169 ◽  
Author(s):  
T.W. Huang ◽  
M.P. Hung ◽  
T.S. Chin ◽  
H.C. Ku ◽  
S.C. Yang ◽  
...  
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Solid State ◽  
Activation Energies ◽  
Kcal Mole ◽  
Preparation Methods ◽  
High Tc ◽  
Superconducting Phases ◽  
The One ◽  
Flowing Oxygen

AbstractDifferential thermal analysis (DTA) and thermal gravitometry analysis (TG A) under flowing oxygen show that the formation temperatures of the high Tc T12Ca2Ba2Cu3Ox (2223) and the low Tc T12CaBa2Cu2Ox (2212) phases lie at around 910 °C and 840 °C, respectively. The activation energies are as low as 50 kcal/mole for the 2223 phase and 35 kcal/mole for the 2122 phase. Thus the time for the formation of these phases can be within 30 minutes.Two preparation methods were tried, and the one with Ca3BaCu3O7 as a precursor was easier to attain pure high Tc 2223 phase than that prepared directly from component oxides and carbonates.

An Approach to the Thermodynamics of Histological Dyeing, Illustrated by Experiments with Azure A

1963 ◽  
Vol s3-104 (68) ◽  
pp. 413-439
Author(s):  
D. J. GOLDSTEIN
Keyword(s):  
Activation Energy ◽  
Mast Cell ◽  
Activation Energies ◽  
Cartilage Matrix ◽  
Differential Staining ◽  
Standard Free Energy Change ◽  
Kcal Mole ◽  
High Affinity ◽  
Azure A ◽  
T1 And T2

Methods are proposed for the estimation of the rate, activation energy, heat, and affinity of staining of histological sections, and approximate results are given for the staining of mucin, mast-cell granules, chromatin, cytoplasmic ribonucleic acid (RNA), cartilage matrix, and other structures by azure A. The half-staining time t½ is the time taken by a substrate under given staining conditions to achieve half the intensity of staining it would reach at equilibrium, and is approximately equal to the time taken to stain in a given, fairly dilute dyebath to the same intensity as at equilibrium in a dyebath of half the given concentration. The activation energy E of staining is given by E = ln t½(1)/t½(2) x RT1T2/(T2-T1), where t½(1) and t½(2) are the half-staining times at absolute temperatures T1 and T2 respectively, and R is the gas constant. The activation energy of staining reflects the effect of temperature on rate of staining, and may be regarded as an index of substrate permeability. Half-staining times and activation energies of staining with azure A increase in the order mucin, mast-cell granules, chromatin, RNA, and interstitial cartilage matrix. Times of half-destaining and activation energies of destaining also are probably largely determined by substrate permeability. Differential staining dependent on differences in rate of staining may be enhanced by the use of chilled and stirred dyebaths, and by the use of dyes of large particle size. The heat of dyeing δH, sometimes regarded as the sum of the heats of formation of the various dye-substrate bonds, approximately equals RT1T2/(T2-T1)x ln [D]1/[D]2, where [D]1 and [D]2 are the concentrations of dyebath giving equal intensity of staining of the substrate at equilibrium at temperatures T1 and T2. Approximate figures for δH in kcal/mole for staining with dilute azure A are: mucin, -8; chromatin and cartilage matrix, -7; cytoplasmic RNA, -5.5; mast-cell granules, - 2 to - 4. The higher the value of -δH the more is staining inhibited by a rise in temperature of the dyebath. The affinity of a dye for a substrate may be regarded as the standard free energy change accompanying the staining process, which under certain conditions is given approximately by δF° = - RT ln τ /(1-τ)[D], where τ is the fraction of available staining sites in the substrate occupied by dye when the substrate is at equilibrium with a dyebath of concentration [D]. Differential staining of substrates with a high affinity for the dye is facilitated by the use of dilute dye solutions. Approximate values of δF° for staining with azure A at 4° C and pH 4.0, in kcal/mole, are: cartilage matrix, -3.8 (orthochromasia) and - 5.3 (metachromasia); mast-cell granules, -4 (orthochromasia) and -4.4 (metachromasia); RNA, -3.1; mucin, between - 2.7 and -3.4; chromatin, -3.1; thyroid colloid, -2.3; Xenopus poison gland secretion, -2.3 It is suggested that part of the high affinity of sulphate groups for basic dyes is due to an increase in entropy during staining, resulting from dispersion of a large hydration shell surrounding the sulphate groups before attachment of the dye.

Sign in / Sign up

Export Citation Format

Share Document