The Reactions of Organometallic Compounds Involving Silicon. Reactions of Triphenyl-, Diphenylmethyl-, and Phenyldimethylsilyl-lithium with 9-Phenylfluorene in Tetrahydrofuran

1972 ◽  
Vol 50 (23) ◽  
pp. 3761-3766 ◽  
Author(s):  
M. A. Hamid
Keyword(s):  
Low Temperatures ◽  
Initial Rate ◽  
Organometallic Compounds ◽  
Initial Reactant ◽  
Thermodynamic Constants ◽  
Rate Of Reaction ◽  
Stop Flow

Triphenyl-, diphenylmethyl-, and phenyldimethylsilyl-lithium react very rapidly with 9-phenylfluorene in tetrahydrofuran (THF) but the reaction can be followed spectroscopically using the stop-flow technique at low temperatures. The order of reaction, found from the dependence of the initial rate of reaction on the initial reactant concentrations, is unity in both 9-phenylfluorene and the relevant organosilyl-lithium reagent. The thermodynamic constants of activation for the reaction between 9-phenylfluorene and triphenylsilyl-lithium (Ph3SiLi), diphenylmethylsilyl-lithium (Ph2MeSiLi), and phenyldimethylsilyl-lithium (PhMe2SiLi), respectively, are: ΔH≠ = 4.5, 4.0, and 4.0 kcal mol−1; ΔG≠ = 13.0, 12.5, and 12.5 kcal mol−1; ΔS≠ = −34.9, −34.8, and −34.9 cal mol−1 deg−1

The Reactions of Organometallic Compounds Involving Silicon. Reactions of Methyldiphenyl-, Triphenylsilyl-sodium, -potassium, -rubidium, and -caesium with 9-Methylfluorene in Tetrahydrofuran

1973 ◽  
Vol 51 (16) ◽  
pp. 2759-2764 ◽  
Author(s):  
Muhammad Abdul Hamid
Keyword(s):  
Dipole Moment ◽  
Binding Energy ◽  
Electronic Transition ◽  
Low Temperatures ◽  
Organometallic Compounds ◽  
Ion Pair ◽  
Sodium Potassium ◽  
Metal Compounds ◽  
Thermodynamic Constants ◽  
Stop Flow

The reactions of triphenylsilyl-sodium(Ph3SiNa), diphenylmethylsilyl-sodium(Ph2MeSiNa), triphenylsilyl-potassium (Ph3SiK), triphenylsilyl-rubidium (Ph3SiRb), and triphenylsilyl-caesium (Ph3SiCs) with 9-methylfluorene in tetrahydrofuran (THF) were studied using the stop-flow technique at low temperatures. The rate constant k (1 mol−1 s−1) depends on the nature of the cation; at −50 °C k is 11.5 for Ph3SiNa, 29.5 for Ph2MeSiNa, 26.8 for Ph3SiK, 35.6 for Ph3SiRb, and 47.9 for Ph3SiCs. It seems that the organosilylalkali–metal compounds (R3SiM) exist in the form of contact ion-pair and therefore the reactivity of an ion-pair is determined by the Coulombic binding energy of the pair. The thermodynamic constants of activation for these reactions were calculated for −50 °C and compared with the corresponding values of triphenylsilyl-lithium Ph3SiLi reaction with 9-methylfluorene in THF. The plots of log k, ΔS≠, and ΔH≠ against 1/(rc + 2) and ΔS≠ against ΔH≠ were drawn to show that Li+ due to its existence as solvent separated ion-pair behaves differently to its Na+, K+, Rb+, and Cs+ counterparts.The electronic spectra of R3SiM, 9-methyl-fluoren-9-yl-sodium, -potassium, -rubidium and -caesium were determined at temperatures varying from 20 to −80 °C. A red shift was observed in spectra of R3SiNa at low temperatures; this was attributed to the increase in dipole moment which occurs during the electronic transition. The spectra of 9-methylfluoren-9-yl-sodium, -potassium, -rubidium, and -caesium were compared with their lithium counterpart to explain the effects of gegenion on the solvation of these species.

The mechanism of the oxidation of thiocyanate ion by peroxomonosulphate in aqueous solution. II. Kinetics of the reaction

1966 ◽  
Vol 19 (8) ◽  
pp. 1365 ◽  
Author(s):  
RH Smith ◽  
IR Wilson
Keyword(s):  
Aqueous Solution ◽  
Initial Rate ◽  
Stopped Flow ◽  
Thiocyanate Ion ◽  
First Order ◽  
Conductance Method ◽  
Rate Of Reaction ◽  
Kinetics Of

Initial rates of reaction for the above oxidation have been measured by a stopped-flow conductance method. Between pH 2 and 3.6, the initial rate of reaction, R, is given by the expression R{[HSO5-]+[SCN-]} = {kb+kc[H+]}[HSO5-]0[SCN-]20+ka[H+]-1[HSO5]20[SCN-]0 As pH increases, there is a transition to a pH-independent rate, first order in each thiocyanate and peroxomonosulphate concentrations.

The slow combustion of aluminium trimethyl

1965 ◽  
Vol 288 (1412) ◽  
pp. 123-132 ◽  
Keyword(s):  
Free Radical ◽  
Organic Compounds ◽  
Initial Rate ◽  
Inert Gases ◽  
Spontaneous Ignition ◽  
Chain Mechanism ◽  
Radical Chain ◽  
Ambient Temperatures ◽  
Slow Combustion ◽  
Rate Of Reaction

Kinetic and analytical studies of the gaseous oxidation of aluminium trimethyl at ambient temperatures and at pressures well below those required for spontaneous ignition have shown that, in contrast to the oxidations of less electron-deficient metal alkyls, no peroxides can be detected and no volatile oxygenated organic compounds are formed. Methane, traces of hydrogen and a solid methoxymethyl compound of aluminium are the only products. The initial rate of reaction is approximately proportional to the first power of the alkyl pressure and to the square of the oxygen pressure; it is little influenced by temperature or by inert gases but is lowered by an increase in surface. The observed kinetic and analytical results can be accounted for in terms of a free radical chain mechanism in which termination takes place predominantly at the walls.

Interaction Of Fibrinogen With Platelets In Plasma

1981 ◽  
Author(s):  
G Marguerie ◽  
M J Larrieu ◽  
E F Plow
Keyword(s):  
Initial Rate ◽  
Platelet Rich Plasma ◽  
Human Platelets ◽  
Affinity Constant ◽  
Single Class ◽  
Fibrinogen Binding ◽  
Rate Of Reaction ◽  
Specific Receptors ◽  
Higher Temperature ◽  
Kinetics Of

Fibrinogen binds to specific receptors on washed human platelets and these sites are induced by ADP. This interaction is assumed to be the basis for the participation of the molecule in ADP-stimulated platelet aggregation, but fibrinogen binding to platelets in plasma has not been directly demonstrated. In this study, we have characterized the binding of 125 I-fibrinogen to platelets in the platelet rich plasma (PRP) of afibrinogene- mic patients. In either citrated or heparinized PRP, association of fibrinogen with platelets was demonstrable and was dependent on ADP dose. This binding was time dependent and reached equilibrium in 10 to 15 min. At 22°C, the rate constants of association were kon = 0.9×10-6 M-1 min-1 in plasma compared to kon = 0.6×l0-6M-1 min-1 in Tyrode’s buffer indicating that initial rate of reaction was similar in both milieu. The kinetics of binding in plasma were the same at 37°C and 22°C but fewer molecules were bound at the higher temperature. In the PRP, saturable binding of fibrinogen to the platelet was achieved at concentrations greater than 0.5 μM. A linear Scatchard plot was derived which indicated a single class of binding site with an affinity constant of Ka = 1.8×106 M-1 and 32,000 fibrinogen molecules were maximally bound per platelet. These values are essentially identical to those obtained with washed platelets. In buffer, platelet-bound fibrinogen becomes progressively nondissociab1e , and this stabilization occurred to a partial extent in plasma. In sum, these results establish that the previously defined steps in ADP-induced binding of fibrinogen to platelet occur in plasma.

scholarly journals A model for the kinetics of activation and catalysis of ribulose 1,5-bisphosphate carboxylase

1976 ◽  
Vol 159 (3) ◽  
pp. 563-570 ◽  
Author(s):  
W A Laing ◽  
J T Christeller
Keyword(s):  
Initial Rate ◽  
Equilibrium Constants ◽  
Co2 Concentration ◽  
Time Dependent ◽  
Enzyme Complex ◽  
Ribulose Bisphosphate Carboxylase ◽  
Ribulose Bisphosphate ◽  
Bisphosphate Carboxylase ◽  
Rate Of Reaction ◽  
Kinetics Of

Further evidence for time-dependent interconversions between active and inactive states of ribulose 1,5-bisphosphate carboxylase is presented. It was found that ribulose bisphosphate oxygenase and ribulose bisphosphate carboxylase could be totally inactivated by excluding CO2 and Mg2+ during dialysis of the enzyme at 4 degrees C. When initially inactive enzyme was assayed, the rate of reaction continually increased with time, and the rate was inversely related to the ribulose bisphosphare concentration. The initial rate of fully activated enzyme showed normal Michaelis-Menten kinetics with respect to ribulose bisphosphate (Km = 10muM). Activation was shown to depend on both CO2 and Mg2+ concentrations, with equilibrium constants for activation of about 100muM and 1 mM respectively. In contrast with activation, catalysis appeared to be independent of Mg2+ concentration, but dependent on CO2 concentration, with a Km(CO2) of about 10muM. By studying activation and de-activation of ribulose bisphosphate carboxylase as a function of CO2 and Mg2+ concentrations, the values of the kinetic constants for these actions have been determined. We propose a model for activation and catalysis of ribulose bisphosphate carboxylase: (see book) where E represents free inactive enzyme; complex in parentheses, activated enzyme; R, ribulose bisphosphate; M, Mg2+; C, CO2; P, the product. We propose that ribulose bisphosphate can bind to both the active and inactive forms of the enzyme, and slow inter-conversion between the two states occurs.

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