Induction period after

H n.m.r. signals but, in addition, the starting material itself is polarized (Porter et al., 1972). Moreover, the appearance of polarization shows an induction period after irradiation is commenced and continues when the irradiation is interrupted for a time longer than the nuclear relaxation... 

Suppose a solid compound A is transformed into B when it is heated at 200°C. An untreated sample of A shows no induction period, but a sample of A that was irradiated with neutrons does show an induction period. After the induction period, the irradiated sample gave similar kinetic behavior to that of the untreated sample. Explain these observations. 

Recent studies demonstrated that the composition of the reaction mixture, and in particular the pH have significant effects on the kinetics of iron(III)-catalyzed autoxidation of sulfur(IV) oxides. When the reaction was triggered at pH 6.1, the typical pH profile as a function of time exhibited a distinct induction period after which the pH sharply decreased (98).The S-shaped kinetic traces were interpreted by assuming that the buffer capacity of the HSO3 / SO3- system efficiently reduces the acidifying effect of the oxidation process. The activity of the... 

If one measures the yield of hydrogen as a function of the radiation dose, there is an induction period after which the G-value of H is constant with time. The results indicate that... 

Figure 1.11 provides an example of H NMR monitoring in the Pd-catalyzed cy-doisomerization of dimethyl diallyl malonate, 39 [28]. The kinetic profile reveals a pronounced induction period after which the exocydic alkene 40a is formed predominantly as the kinetic product. A hydropalladation mechanism was proposed on the basis of NMR experiments, and the transient spedes 41, formed by allylpalla-dation of the coordinated diene, could be detected and identified with the help of and labeling. The hydride Pd catalyst, 42, would be generated from 41 by water-promoted P-hydride elimination. The observed induction period is assodated with the formation of the Pd-hydride 42. 

Results obtained in glass apparatus are summarized in Figure 1. The unsaturation falls off nearly linearly after a short induction period. After the hydroperoxide functional groups attain their maximum, the olefin disappearance decreases and becomes nonlinear as it is consumed by reaction to form polymeric dialkyl peroxide functions. The maximum concentration of polymeric dialkyl peroxide occurs well after the maximum alkenyl hydroperoxide concentration, giving the appearance of a sequential oxidation mechanism. Infrared and gas-liquid chromatographic analyses showed that hydroxylic derivatives, carbonyl derivatives, and lower molecular weight olefins continued to build up as by-products as the oxidation proceeded, as does the acidity titer. 

Zeolite crystallization can be interpreted in terms of a ripening mechanism. The initially formed gel consists of amorphous dispersed particles of the order of 100-300 A in size. Growth of these particles to approximately 1000 A occurs during the induction period after which zeolite crystals appear imbedded in the amorphous gel matrix. This is especially evident in electron microscopic studies of gel solids (66,88). Ciric comments on the observation of growing crystals imbedded in gel particles which, as the crystals grow, tend to shrink together, resulting in coalescence (74)-... 

When the metal surface is not sufficiently activated, dehalogenations with metals start after an induction period. After the addition of some or all of the substrate, and on agitation of the mixture with heating, an exothermic dehalogenation may start so violently that sometimes it cannot be controlled. 

Table II is a summary of results obtained with soluble bis(cyclopenta-dienyl)titanium compounds as catalysts (52-56). The activity for polymerization increases in each run after a short induction period. After reaching a maximum, a continuous decrease in activity is observed as a consequence of rapid aging processes, such as alkyl exchange, hydrogen transfer, and reduction of the titanium. The average activity is 7-200 kg of PE...

Although the instantaneous quantum yield may generally change with time of irradiation, in conventional experiments at constant light intensity there is often only a short initial period during which the instantaneous quantum yield increases, and then it reaches a constant value. The initial part is called the "induction period." After the instantaneous quantum yield becomes constant, the system is said to be in a stationary or steady state. Under these conditions, it is the steady-state quantum yield which is obtained. Provided that the induction period represents only a small fraction of the total irradiation time and that the quantum yield does then become constant, the overall quantum yield will also be independent of irradiation time and is practically equal to the steady-state quantum yield. 

The Mn(TRPyP) catalytic mechanism was elucidated (278,279) by monitoring the concentrations of the products as a function of the time, showing typical zero-order kinetics (Fig. 29). There is a short induction period, after which the concentration of all products increase linearly as a function of the reaction time for at least two half-lives. 

Fig, 24, OH concentration profiles, showing the effect of the exchange initiation reaction on the growth of OH during the first 75 fisec of the induction period (after Ripley and Gardiner [112]). Profiles calculated for 1 1 98, H2 02 Ar mixture at... 

A third Pt surface on which oscillations of the CO/O2 reaction have been observed is the (210) plane (75,78). In this case, a surface-phase transition was again proposed as an explanation for the oscillations. The (210) surface was observed to facet into (310) and (110) orientations during an induction period, after which oscillations began to occur on the (110) facets (78). An alternative model for the oscillatory behavior has been proposed by Ehsasi et al. (76). 

Reactions were run in 15 mL of toluene, At about 3000 s, 0,20 g of PS-SO Ag was added The hydrogenation rate measured before this addition was the initial rate. After the PS SO Ag was added there was an induction period after which the final rate was measured. H2 uptake stopped until 350 s after the addition of PS-SO Ag. cThe initial rate decreased to 0 mmol H2/s after 400 s and was 0 at the time the PS-SO Ag was added. 

Unfortunately, in reality, at the beginning of the polymerisation reaction the solubility of PO in the polyolic starters (for example in molten sorbitol) is lower than in the adducts of PO to sorbitol. As an immediate consequence, an initial lower consumption rate of PO (in spite of the presence of two reactive primary hydroxyl groups in sorbitol) takes place (induction period). After the addition of 2-3 mols of PO/mol of sorbitol, the solubility of PO in the reaction mass increases substantially and the PO polymerisation reaction is strongly accelerated. Figure 13.7 shows the PO consumption with time in the propoxylation of sorbitol at 120 °C. It is observed that after a short induction period of 40-60 minutes, the PO consumption is markedly accelerated. 

Srikantan and Rao (79) reported that the ferrocyanide catalysis is not first order in peroxide as found by Kistiakowsky but much more complicated. No details of the experiments were given. They also studied the ferricyanide-peroxide reaction and found that in the dark there was a pronounced induction period after which the decomposition rate was first order in peroxide concentration. Illuminating for five minutes in bright sunlight removed this induction period but the subsequent first order rate is somewhat less than the original dark rate. They suggest that the induction period was the time taken to build up on... 

The yield of CO is plotted versus irradiation time in Figure 2. The CO yield was not linearly correlated with irradiation time but showed an induction period. After irradiation for 20 min, when the absorbance at 450 nm reached a maximum, only trace amounts of CO were detected. It is noteworthy that after the 50-min irradiation, the CO yield significantly increased when the solution was stored in the dark before the addition of air. The CO yield reached 50% of the amount of [Ni(bpy)3](Cl04)2 used at 100 min. These results suggest that a two-step reaction takes place in the presence of CO2. 

The end products were obtained by carrying out runs under usual kinetic conditions. Vigorous evolution of H2S occurred after the induction period. After the mercaptan was consumed completely, the residual mixture was extracted several times with ethanol and diethyl ether. In experiments with thiophenol, diphenyldisulfane and an oily residue were... 

Oxidation of cyclohexene by polymeric cobalt-containing catalysts [132,133] has many significant features. In the presence of Co(AcAc)2 (AcAc = acetyl-acetonate) the process is characterized by an induction period, after which the rate rapidly reaches its highest value and decreases thereafter (Fig. 12-10, plot 1). 

The rate of heat evolution keeps at the low value to about 1 hours for the control cement, and to about 4 hours for the cement with SBR dispersion or powder, indicating the SBR dispersion or power prolongate the cement hydration induction period. After the induction period, the second exothermic peak appears, shown in Fig. 1 (b), which is corresponding to the acceleratory and decelera-tory periods of the cement hydration. Here, the influence of the SBR dispersion and powder is different. The influence of the SBR dispersion on the exothermic peak is much more significant. The appearing time of the maximum rate of heat evolution is delayed from 10 hours to 16 hours with the SBR dispersion addition, and the maximum rate decreases markedly from 3.1 mW/g to 1.8 mW/g. Whereas with the SBR powder modification, the appearing time of the maximum rate of heat evolution is delayed from 10 hours to 12.5 hours, and the maximum rate decreases from 3.1 mW/g to 2.9... 

By contrast, widely different individual force (reaction) profiles were observed for the aminolysis reaction. Most of the profiles showed an induction period, after which the puU-ofif forces increased and finally leveled off. A number of representative individual traces are shown in Fig. 10a. Figure 10b shows a histogram of the induction periods observed for the aminolysis, as well as a plot of the experimentally determined induction period vs the number of effectively interacting molecular pairs (evaluated by the JKR [145] and the Poisson [ 146] approaches, respectively). 

The hydration of CA is accompanied by a liberation of heat of hydration. In paste hydration at ambient temperature the rate at which heat is liberated is slow initially, but a heat hberation maximum develops at the end of an induction period, after which time the rate of the hydration reaction is significarrtly accelerated. The time at which the maximttm heat output (ranging up to about 800 W/kg Edmonds and Majirmdar, 1988) is reached becomes extended as the temperature increases from 0°C up to about 30°C, indicating a gradual slow-down of the hydration reaction. At even higher temperatures. 

It has been established experimentally that the number of nuclei deposited electro-lytically onto an inert electrode increases linearly with time after an induction period. After a sufficient length of time, it reaches a saturated value that is independent of time. The density of the saturation value increases with the increasing applied overpotential and is strongly dependent on the concentration of the electrolyte and the state of the electrode surface [55]. 

The reaction of hydrosilylation was investigated without solvent in the presence of catalysts at temperature range 80-90°C. In both cases the hydrosilylation proceeds with an inductive period, after that the reaction proceeds autocatalytic with the formation of three-dimensional systems. 

It is characteristic that a sharp variation of the value of r as a function of the oxygen pressure is observed only at pressures below 150-200 mm Hg. For such pressures the reciprocal of the induction period 1/ r is also proportional to the average rate of the initial stage of the reaction, directly proportional to the pressure (r Pq = const). A further increase in the pressure (to 120 atm in [10]) has very little influence on the variation of the induction period. After the end of the induction period the absorption of oxygen occurs according to a curve possessinga sharply pronounced autocatalytic character. 

A slurry of 2 (0.2812 g, 40.5 mmol of lithium 6.7343 g, 52.5 mmol of naphthalene 2.2540 g, 17.6 mmol of cobalt chloride) was prepared, and the product separated and washed with three 30 ml portions of diethyl ether. The metal powder in 30 ml of fresh glyme was treated at room temperature with 5.46 g (32 mmol) of benzyl bromide, causing a brisk exotherm after a brief induction period. After 14h the products were quantitatively determined by GC as bibenzyl (63%) and toluene (6%) with use of a known quantity of K-nonane as an internal standard and application of response factor corrections. 

Ru(CO)4l2]. The reaction has an induction period after which the rate equation contains both zero- and first-order terms in I2. The rate constant for the zero-and first-order term is too large to be ascribed to the dissociative step given in equation (7). Formation of an adduct, [Ru(CO)5.l2] is suggested. 

A small amount of trifluoromethanesulfonic acid (1.0 g) was added to tri-butylborane (15.16 g, 83.3 mmol) at room temperature under argon. The mixture was stirred and warmed to 50 °C until evolution of butane began (there is an induction period). After cooling of the mixture to 25 °C the remaining trifluoromethanesulfonic acid (11.51 g, total 83.3 mmol) was added dropwise at such a rate as to maintain a temperature between 25 and 50 °C. 

One of the first study of lamellar-to-lamellar phase transition dynamics was performed on the lamellar phase formed by lipid extracts from E-coli membranes and on the membrane itself by TR-SAXS using a cell with a built-in Peltier element that allowed large T-jumps and rapid cooling of the cell. The time required to achieve the disorder-to-order transition was found to be 1-2 s for the lipid lamellar phases and the membrane. The transformation involved no induction period after the T-jump. Some results suggested that the time course of the transformation involved two relaxation times. 

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