Controllable experiment

The bimodal pore distribution model used by Gibilaro et aL may also be used to analyze the results of this type of experiment. If it is assumed that all extraneous effects due to mixing in the interstices between the pellets have been eliminated by means of a control experiment, the results corresponding to equations (10.39) and (10.40) are now... 

The excess of unchanged acetic anhydride is then hydrolysed by the addition of water, and the total free acetic acid estimated by titration with standard NaOH solution. Simultaneously a control experiment is performed identical with the above except that the alcohol is omitted. The difference in the volumes of NaOH solution required in the two experiments is equivalent to the difference in the amount of acetic add formed, i.e., to the acetic acid used in the actual acetylation. If the molecular weight of the alcohol is known, the number of hydroxyl groups can then be calculated. 

The absolute concentration of a reagent e.g., the exact amount of acetic anhydride in the above pyridine. solution) need not be determined, since if the same amount of the reagent is used in the actual and in the control experiments, the difference gives at once the actual amount used. 

Adventitious losses of the reagent, due, e.g., to the chemical action of the alkaline glass vessels, slight absorption by the corks, etc., are almost identical for the actual and the control experiments and therefore do nor affect the difference in result between the two experiments. 

Control experiment. This is not necessary if the sodium peroxide is known to be chlorine-free. If there is any doubt on this point, the whole operation should be repeated precisely as before, but omitting the organic halogen compound. A small thiocyanate titration value may be found, and this should be deducted from all determinations in which the above quantity of the particular batch of sodium peroxide is used. 

The photochemical behavior of the isomeric 3-methyl-2-phenyl-2-allyl-l-azirine (66) system was also studied. Irradiation of (66) in cyclohexane gave a quantitative yield of azabicyclohexenes (67) and (68). Control experiments showed that (65) and (66) were not interconverted by a Cope reaction under the photolytic conditions. Photocycloaddition of (66) with an added dipolarophile afforded a different 1,3-dipolar cycloadduct from that obtained from (65). The thermodynamically less favored endo isomer (68b) was also formed as the exclusive product from the irradiation of azirine (66b). 

To summarise, unexpected corrosion failures are much more likely to occur by localised attack than by uniform attack (which can easily be detected) and although corrosion handbooks are useful for making initial choices of materials for applications where corrosion is important, critical components must be checked for life-to-fracture in closely controlled experiments resembling the actual environment as nearly as possible. 

Chapters 8 and 9 presented computer codes that are available for computer hazardous material release and transport. Many of these codes have been tested using controlled experiments with varying agreement depending upon the code s applicability to the phenomena. In the author s opinion, the accuracy of the consequence calculation is not much better than the calculation of accident probabilities. 

Perhaps the most widely misunderstood aspect of gauge development is the role of the controlled shock-compression experiment in the development process. It is often stated that the gauges are being calibrated. In fact, it is not possible to calibrate a gauge that must be used over the wide range of conditions and over the wide range of wave profiles encountered and is destroyed in use. Only in special cases of shocks to fixed conditions is the response measured for a gauge in controlled experiments directly a suitable calibration. Even in the direct shock experiment, the controlled shock-compression experiment serves as a shock calibration only if the reproducibility of materials in the sensor is evaluated quantitatively and a persistent reproducible materials source is available. 

These controlled experiments eliminate adsorption as an explanation for the elution order of neutral amino acids from PolyHEA. Perhaps this order does... 

For the overwhelming majority of substances encountered in industry, there are not enough data on toxic responses of humans to permit an accurate or precise assessment of the substance s hazard potential. Frequently, the only data available are from controlled experiments conducted with laboratory animals. In such cases, it is necessary to extrapolate from effects observed in animals to effects likely to occur in... 

The configuration of the amine was retained, except in the case of amino acid derivatives, which racemized at the stage of the pyridinium salt product. Control experiments showed that, while the starting amino acid was configurationally stable under the reaction conditions, the pyridinium salt readily underwent deuterium exchange at the rz-position in D2O. In another early example, optically active amino alcohol 73 and amino acetate 74 provided chiral 1,4-dihydronicotinamide precursors 75 and 76, respectively, upon reaction with Zincke salt 8 (Scheme 8.4.24). The 1,4-dihydro forms of 75 and 76 were used in studies on the asymmetric reduction of rz,>S-unsaturated iminium salts. 

This unexpected outcome clearly implicated an important stereodirecting role for the dioxolane oxygens. To clarify the significance of having oxygen atoms bound to the stereogenic centers. Mash carried out an important control experiment by exam-... 

Gegen-uberstellung, /. opposition contrast comparison, -versuch, m. control experiment. -wart,/. presence present. gegenwMrtig, a. pre.sent. — adv. at present. Gegen-welle, /. countershaft, -wert, m. equivalent. 

Rumford decided to try a more controlled experiment. He placed a brass gun barrel in a wooden box containing about nineteen pounds of cold water, and used a team of horses to rotate a blunt steel borer inside the barrel. After 2.5 hours, the water boiled As Rumford described it, It would be difficult to describe the surprise and astonishment expressed on the countenances of the bystanders on seeing so large a quantity of cold water heated, and actually made to boil, without any fire. ... 

Although trityl perchlorate is used to accomplish the glycosidation of the C-8 hydroxyl in 44 with acetoxy glycoside 49, control experiments have demonstrated that no reaction takes place in the presence of 4 A molecular sieves or 2,6-di-terf-butylpyridine. This observation suggests that the actual catalyst is not trityl perchlorate, but perchloric acid. Consistent with this conclusion is the observation that catalytic amounts of a strong Brpnsted acid such as triflic or perchloric acid can catalyze the glycosidation of 44 with 49 in the absence of trityl perchlorate. 

The tautomerization is induced by cobalt(II) which forms the thermodynamically more stable metalatcd hydroporphyrins from which the cobalt can be removed using trifluoroacctic acid under kinetic control. Experiments with porphyrinogen and hexahydroporphyrin show that the porphyrinogen-hexahydroporphyrin equilibrium can be shifted by complexation of porphyrinogen with metal ions to the more stable metal hexahydroporphyrins and that metal-free hexahydroporphyrins tautomerize back to the more stable metal-free porphyrinogens.29... 

Fig. 1.14 Relationship between the incorporation of 180 into product CO2 and the amount of luciferin used, in the bioluminescence reaction of Cypridina luciferin catalyzed by Cypridina luciferase. The reactions were carried out in H2160 medium with 1802 gas (solid line) in H2lsO medium with 16C>2 gas (dashed line) and the control experiment of the latter using C16C>2 gas instead of luciferin and luciferase (dotted line), all in 20 mM glycylglycine buffer, pH 7.8, containing 40 mM NaCl. From Shimomura and Johnson, 1973a. Reproduced with permission from Elsevier.

Fig. 7.2.9 Influence of cyanide and iodine on the Odontosyllis luciferin-luciferase luminescence reaction. Luciferin solution (0.1 ml) was first mixed with a HCN solution (0.1ml), and then the mixture was injected into 8 ml of 20 mM magnesium acetate containing luciferase. The concentrations of HCN shown in the figure are the final concentrations. In the control experiment, HCN was omitted. In the experiment labeled added at 0.5 min, 0.1 ml of HCN solution was injected to the control mixture 0.5 min after the start of the luminescence reaction to give a final concentration of 0.1 mM HCN. Arrows indicate the injection of a solution of I2-3KI to the control mixture to give a final concentration of 0.1 mM I2. From Shimomura et al., 1963d, with permission from John Wiley Sons Ltd.

Control experiments, performed with the ( + )-(R)-diastereomer of 1, which differs only in the configuration of the stereogenic center at the metal, afford the enantiomeric homoallylic alcohol, (S)-3-methyl-1-phenyl-3-butenol, also with high enantiomeric excess, indicating that the chiral cyclopentadienyl ligand has no dominating influence1-2. 

Many of the above-mentioned complications can be avoided or allowed for by carrying out appropriate control experiments. A further difficulty lies w ith the... 

In the course of the above preliminary experimentation we have discovered that the H20 /EtAlCl2 system (i.e. control experiments) readily yields unusually high... 

Concentrations. At least one of the reactants will accelerate the reaction. A product may as well, in which case the reaction is said to be product-catalyzed or auto-catalyzed. A product may instead inhibit the reaction, sometimes but not necessarily because the reaction does not proceed to completion. A catalyst may also affect the rate. One makes every effort to know whether a catalyst is unintentionally present. The effects of trace impurities cannot be discounted without control experiments. 

The novel highly substituted spiro[4.4]nonatrienes 98 and 99 are produced by a [3+2+2+2] cocyclization with participation of three alkyne molecules and the (2 -dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 (Scheme 20). This transformation is the first one ever observed involving threefold insertion of an alkyne and was first reported in 1999 by de Meijere et al. [81]. The structure of the product was eventually determined by X-ray crystal structure analysis of the quaternary ammonium iodide prepared from the regioisomer 98 (Ar=Ph) with methyl iodide. Interestingly, these formal [3+2+2+2] cycloaddition products are formed only from terminal arylacetylenes. In a control experiment with the complex 96 13C-labeled at the carbene carbon, the 13C label was found only at the spiro carbon atom of the products 98 and 99 [42]. 

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