Constants, Covers

Inversion at the N center is coupled to conformational changes in a chelate ring. The kinetics of inversion at asymmetric N centers in complexes of tetraaza linear or macrocyclic ligands have received scant attention. There are five configurational isomers of the planar complex Ni([14]aneN4) +, Sec. 3.1.1. The interconversions between such structures are base catalyzed with second-order rate constants covering a small range from 1.2 x 10 to 2.4 x 10 M- s- Refs. 108-110. 

The above effect is explained by the spatial extent of the initial wavepacket on the potential surface. A larger wavepacket (smaller force constant) covers more of the potential, experiences a larger slope in the Qx dimension, and therefore increases the width of the low frequency progressions because the initial decrease in the overlap is fast. Conversely, a smaller wavepacket (larger force constant) covers less of the potential, experiences a smaller slope in the Qx... 

The NMR method (Dynamic NMR DNMR) 16> of determining rate constants covers a range of rates corresponding to barrier heights from 5—6 kcal/mole to 20—25 lccal/mole. This range lies in between the domains where microwave spectroscopy (below) or classical kinetic methods (above) may be used. 

More recent approaches [42], based on studies with isolated leaf cuticles in vitro with a wide range of formulations, considered transport through the cuticle to be a three stage diffusion mechanism, namely absorption into the cuticle, diffusion through the cuticle and finally desoiption from the cuticle into the internal leaf cells. This experimental method used a constant cuticular area, constantly covered by a volume of spray solution, so variable spreading was not an issue. An alternate version of this approach uses droplets applied to cuticular membranes which is more realistic [43]. The modified Pick s equation used in these in vitro studies [41,42] has the following form ... 

The experimental verification of such a complex rate expression is usually carried out by varying the concentrations of a single conjugate acid-base pair at a time. In the mutarotation of glucose in water solution at 18°C, ko is found to be 0.0054, while for acetate ion, /cac- = 0.0265 for phenoxide ion, = 4.4 and for 011 it is 3800. For catalysis by ku is found to be 0.0040 liter/mole-min. It can be seen that the constants cover an exceedingly large range. 

In the converse application of the explicit relation between F and G matrices and thermodynamic quantities, a set of effective harmonic force constants covering a certain range of temperature is derived from experimental data on a strongly temperature-dependent property obtained in the same temperature range. The least-squares process becomes non-linear... 

This wide range in thermal stability, that is, relative rate constants covering 13 orders of magnitude or a difference in activation energies of 17kcal/mole, is impressive. In more tangible terms, the half-life of the iminodioxetane (Entry 1 in Table 4) is about 0.1 sec at 20°C for the diadamantylidenedioxetane (Entry 30 in Table 4), it is about 20,000 years at this temperature. This is truly a remarkable variation in the thermal stability of these unusual substances. 

Pour the so In on the column and apply gentle suction. Wash beaker with two small successive portions of l 4-benz-petr eth mixture, while keeping the top of the column constantly covered with liquid... 

Adiabatic calorimeter. With the adiabatic calorimeter, exchange of heat between the calorimetric vessel and the cover is suppressed. This happens so that the temperatures of the vessel and the cover are maintained at almost the same temperature. The condition (Tc-Tfi) = 0 can be attained at constant cover temperature by heating or cooling the calorimetric vessel using an internal heater or heat sink placed inside the calorimetric vessel. This compensation method is suitable for endothermic processes. For the adiabatic method, the characteristic feature is not only the equality of temperatures of the calorimetric vessel and of the cover, but also their changing value - the measurement proceeds at dynamic conditions, where the temperature of the calorimetric cover follows the temperature of the calorimetric vessel. 

In Table 1 the reactivities of some organosilanes toward primary alkyl radicals are reported. The rate constants cover a range of several orders of magnitude and, therefore, the hydrogen donating abilities in organosilanes can be modulated by the substituents. 

Soils formed in areas where a constant cover of grass has been present for hundreds of years are usually among the most fertile of all of our agricultural soils and, apart from... 

These results provide the first detailed calibration for a series of intramolecular radical cation probes based on cycloaddition chemistry. The cyclization rate constants cover several orders of magnitude in timescale, an ideal case for using 1—3 as probes for radical cations of different lifetimes. However, the time-resolved experiments demonstrate that the application of radical cation probes, at least those based on aryl alkene cycloaddition chemistry, may be considerably less straightforward than similar experiments with free radical probes or clocks. Some of the problems that need to be addressed include the variation of products with the reaction conditions and method of radical cation generation, and the possibility of reversibility of the initial adduct formation. Furthermore, at least some radical cation reactions are quite sensitive to solvent and this may mean that calibrations for radical cation cycloadditions will have to be done in a variety of solvents. 

A graph of log D versus T" thus allows the determination of Q and D. The values of these constants cover a rather wide range, and, because of the exponential nature of the equation, a small error in Q can result in large errors in the calculation of Dq. In the atomistic models of diffusion [81], Dq is related to the frequency of the atomic jumps... 

Other researchers [61] also proposed average values for the Mark-Houwink constants covering a certain range of DDA. 

Handbook of Chemistry. New York McGraw-Hill Book Company, N.A. Lange, Ed. Essentially paralleling the handbook above, this one is revised about once every five years. Its tables of constants cover about half as many compounds as the CRC handbook. 

In Table 103 Carson s (49) data have been converted to absolute permeabilities, and show the range of permeability constants covered by the paper section of group C of Fig. 132. 

The inner coat of the stomach, Beaumont said, is constantly covered with a... 

The effect of solvent choice on initiation rate has also been explored. Sanford et al. suggested a tentative link between dielectric constant and initiation rate for G1 and G2, based on a small set of initiation rate data (Table 2.3, entries 1—8). However, a later study by Percy and Nelson with a wider set of solvents established that no such link exists for G2 (Table 2.3, Entries 9—17). In addition, the initiation rate constants cover a relatively small range. Notably, initiation is slowest in hexafluoroben-zene, which is interesting given reports of its accelerating effects on alkene metathesis reactions, even as part of a solvent mixture. 

Data on the occurrence of lichen substances and their physical constants covering the literature up to 1976 can be found in Culberson s guide (C.F. Culberson 1969, 1970a C.F. Culberson et al. 1977b). 

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