Yield rate

For some experiments, the solar neutrino flux and the rate of decay of the proton being extreme examples, tire count rate is so small that observation times of months or even years are required to yield rates of sufficiently small relative uncertainty to be significant. For high count rate experiments, the limitation is the speed with which the electronics can process and record the incoming infomiation. 

No kinetic studies, which have yielded rate coefficients of nitrodesilylation... 

Mean Residence Time,T,hr. Base Case Yields Rate Constant 0.0524 cm/sec Lifetime, X=18.3 hr. Size dy= 0.0005 cm (+ks =0.01384) Temp., T=71°C Pressure P=261.8 psig Composition C3H0,Inerts. 76,. 24... 

The quantum yield for the formation of the cycloaddition product has been found to be temperature dependent, increasing by a factor of approximately three as the temperature is lowered from 65 ( = 0.24) to 5°C ( = 0.69). Photolysis of mixtures of the olefin and f/my-stilbene in the presence of sensitizers yielded no cycloaddition product (42) but rather only m-stilbene. This suggests that the cycloadduct is produced via a singlet reaction. This conclusion is supported by the fact that tetramethylethylene quenches fluorescence from the /rans-stilbene singlet. A plot of l/ (42) vs. 1/[TME] (TME = tetramethylethylene) is linear. The slope of this plot yields rate constants for cycloadduct formation which show a negative temperature dependence. To account for this fact, a reversibly formed exciplex leading to (42) was proposed in the following mechanism<82) ... 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

The reaction mixtures were clear and colourless at temperatures below about -15° the polymer came out of solution during the reaction. The half-lives of the reactions ranged from 2 to 60 s, the yield, rate, and DP were uninfluenced by the sequence in which the catalyst phial and water phial were broken, the DP of the polyisobutenes ranged from 20 to 2 x 105, and elementary and spectroscopic analyses showed the polymers to contain chlorine, OH-groups and vinyl and tri-substituted double bonds. 

Note The kinetic shift denotes the overestimation of AEs due to the contribution of excess energy in the transition state necessary to yield rate constants larger than 10 s The determination of lEs does not suffer from kinetic shift as there are no kinetics involved in electron or photon ionization. 

Concerted acid-base catalysed enolizations of a range of simple aldehydes and ketones have been measured in water at 25 °C, using a range of substituted acetic acid-acetate buffers.The buffer plots yield rate constants for acid (A a) and base ( b) catalytic terms in the normal way at low buffer concentrations. Extension up to higher concentrations (as far as [total buffer] = 2 m, typically) yields the third-order term ( ab) via upward curvature of the plots. While ab does not have a simple correlation with either k or b, it does correlate with their product, i.e. 

Transition state theory yields rate coefficients at the high-pressure limit (i.e., statistical equilibrium). For reactions that are pressure-dependent, more sophisticated methods such as RRKM rate calculations coupled with master equation calculations (to estimate collisional energy transfer) allow for estimation of low-pressure rates. Rate coefficients obtained over a range of temperatures can be used to obtain two- and three-parameter Arrhenius expressions ... 

Data collected for each run included acid analysis using inductively coupled plasma (ICF) to determine cation concentration and titration to determine H concentration. Filtering characteristics were determined using solid and filtrate yield rates, as well as back pressures during the filtration cycle. The filter cake was characterized by moisture content and composition. Solid samples were analyzed with scanning electron microscopy (SEM) to determine changes in particle shape and size under various process conditions, and X-ray diffraction (XRD) was used to determine the solids composition. 

Pressure, Pressure, No. of Yield Rate, Salinity, % Sea Water... 

A comparison of steric influence resulting from more than 80 different silyl groups is summarized in Table 1. The trend is established on the basis of reaction yields, rates and selectivity, as well as on reactivity and physical properties of organosilanes. Two different effects may be involved (a) the effect of a silyl group on reactions taking place at the neighboring centers, and (b) the effect of the groups attached to silicon on the nucleophilic attack at the silicon atom. 

More directly, a proposed intermediate may be generated from alternative precursors, in non-equilibrium concentrations, under conditions quite close to those of the reaction in question. Fast kinetic methods may then yield rates for decay of the intermediate, and products may be determined for comparison with observations on the reaction in question. The reader is directed to the recent review edited by Moss, Platz and Jones Jr. [10], for a modern comprehensive survey of progress in reactive intermediate chemistry. The chapters deal in some detail with the methods touched on as outlined above and the results of their application to carbocations, carbanions, carbenes, radicals and strained species. 

The partial rate factors for the substitution reactions of biphenyl, with the exception of a few observations, are on a firm experimental basis. The chlorination of biphenyl was examined on several occasions (de la Mare et al., 1958a Beaven et al., 1961 Mason, 1959 Dewar and Mole, 1957). There are significant differences in the reported values for the rate relative to benzene. A recent careful examination of the products (Beaven et al., 1961) indicated the formation of 2- and 4-chloro-biphenyl in 76.5% yield with 17.5% of the residual chlorine consumed via addition processes. The partial rate factors presented in the table are corrected on this basis. Two early studies of the nitration of biphenyl with acetyl nitrate in acetic anhydride yield rate data in poor agreement (Dewar et al., 1956 Simamura and Mizuno, 1957). A recent re-examination of the problem (Billings and Norman, 1961) yielded partial rate factors (ofh = 36.4 = 32.6) confirming the results... 

The field of indoor chemistry has moved out of its infancy to a robust adolescence. Questions remain, but product yields, rates and mechanisms have been... 

The optical and PL spectroscopies have been undertaken to understand the structure-property correlations of this important family of triplet-emitting polymers. The red shift in the absorption features upon coordination of the metal groups is consistent with there being an increase in conjugation length over the molecule through the metal center. The trade-olf relationship between the phosphorescence parameters (such as emission wavelength, quantum yield, rates of radiative and nonradiative decay) and the optical gap will be formulated. For systems with third-row transition metal chromophores in which the ISC efficiency is close to 100%,76-78 the phosphorescence radiative (kr)y, and nonradiative (/cm)p decay rates are related to the measured lifetime of triplet emission (tp) and the phosphorescence quantum yield ([Pg.300]

Microreactors offer a radical alternative platform for chemical synthesis, normally undertaken in macroscale flasks [68-70]. When reactions in microcapillary-scale reactors are compared with those in flask-scale batch reactors, they have been shown to offer yield, rate or selectivity advantages in a diversity of reactions schemes including carbonylative cross-coupling of arylhalides to secondary amides [32],... 

The observations in kinetic studies are usually concentration or conversion measurements. CSTRs and differential PFRs yield rate data directly, so the experimentally observed rate can be directly fitted on the rate expression and its parameters estimated. 

Nitrogen dioxide Nitrate Nitrite Ozone Photochemistry Quantum yield Rate law... 

---