Nef reaction TFaP


Since 1970 a variety of reaction classification schemes have been developed to allow a more systematic processing of the huge variety of chemical reaction instances (see Chapter III, Section 1 in the Handbook). Reaction classification serves to combine several reaction instances into one reaction type. In this way, the vast number of observed chemical reactions is reduced to a manageable number of reaction types. Apphcation to specific starting materials of the bond and electron changes inherent in such a reaction type then generates a specific reaction instance.  [c.183]

Such an analysis of the Hterature for assigning reaction types to different reaction schemes definitely has merits. However, it does not say anything about the importance of a reaction type, such as how frequently it is actually performed in the laboratory.  [c.189]

HORACE used alternating phases of classification (which topological or physicochemical features are required for a reaction type) and generalization (which features are allowed and can be eliminated) to produce a hierarchical classification of a set of reaction instances.  [c.193]

Reactions belonging to the same reaction type are projected into coherent areas on the Kohonen map this shows that the assignment of reaction types by a chemist is also perceived by the Kohonen network on the basis of the electronic descriptors. This attests to the power of this approach.  [c.196]

For each individual mechanistic reaction type, quite an elaborate heuristic decision scheme was built to arrive at rules that allow one to make predictions on specific reaction queries.  [c.549]

After the definition of a reaction type, a scheme for the evaluation of the given reaction type can follow in the reaction rule. An entire hierarchy of evaluations can be implemented, from no evaluation at all to a full-fledged estimation of reaction kinetics [12  [c.551]

The more details of a reaction type are available, the better can be the modeling of a reaction of that type.  [c.592]

Reduction of arenes by catalytic hydrogenation was described m Section 114 A dif ferent method using Group I metals as reducing agents which gives 1 4 cyclohexadiene derivatives will be presented m Section 1111 Electrophilic aromatic substitution is the most important reaction type exhibited by benzene and its derivatives and constitutes the entire subject matter of Chapter 12  [c.438]

Although the present chapter includes the usual collection of topics designed to acquaint us with a particular class of compounds its central theme is a fundamental reaction type nucleophilic addition to carbonyl groups The principles of nucleophilic addition to aide hydes and ketones developed here will be seen to have broad applicability m later chap ters when transformations of various derivatives of carboxylic acids are discussed  [c.703]

Before leaving this mechanistic discussion we should mention that the addition-elimination mechanism for nucleophilic aromatic substitution illustrates a prm ciple worth remembering The words activating and deactivating as applied to substituent effects m organic chemistry are without meaning when they stand alone When we say that a group is activating or deactivating we need to specify the reaction type that is being considered A nitro group is a strongly deactivating substituent in electrophilic aromatic substitution where it markedly destabilizes the key cyclohexadienyl cation intermediate  [c.979]

Electrophilic aromatic substitution (Section 12 1) Fundamen tal reaction type exhibited by aromatic compounds An electrophilic species (E" ) attacks an aromatic ring and re places one of the hydrogens  [c.1282]

Reaction type Group a- or y-groups Compare with  [c.82]

Although some of the oxidative ring closures described above, e.g. reactions with lead tetraacetate (Section 4.03.4.1.2), may actually involve radical intermediates, little use has been made of this reaction type in the synthesis of five-membered rings with two or more heteroatoms. Radical intermediates involved in photochemical transformations are described in Section 4.03.9. Free radical substitutions are described in the various monograph chapters.  [c.141]

Turboexpanders can be classified as either axial or radial. Axial flow expanders have either impulse or reaction type blades and are suitable  [c.1131]

Reaction-Type Crystallizers. 18-47  [c.1621]

FIG. 18-68 Swenson reaction type DTB crystallizer. (Swenson Process Equipment, Inc.)  [c.1666]

The thermodynamic properties of the solid silicates show the expected entropy change of formation from the constituent oxides of nearly zero, which is typical of the reaction type  [c.308]

A further improvement in turbine design led to the radial reaction type seen in Figure 2-3. Compared to the pure reaction type, the radial reaction machine has a reduced discharge diameter. In this design the gas, again half expanded in the primary nozzles and jetted tangentially into the rotor, matches the peripheral speed of the rotor and flows radially inward within the rotor, leaving it at a lesser diameter. This arrangement reduces the velocity required from the secondary (rotor)  [c.20]

More specifically, there are two general geothermal resources dry steam fields and wet brine fields. In the dry geothermal fields, energy is recovered from the expansion of steam flashed from the hot well streams. Thousands of megawatts are being produced from such dry geothermal steam fields in Northern California and Washington State in the U.S. A typical application is Unocal s geothermal power plant in the Salton Sea, located in Imperial Valley, California. In this project, the high pressure steam (23 bar) from the separator is directed through a Rotoflow turboexpander operating at a back-pressure of about 9 bar. The turboexpander is a 15,000 rpm radial inflow, variable inlet vane, reaction-type turbine, with a power output rating of 4.4 MW. This unit has been in commercial operation since 1990.  [c.136]

Figure 4-110 depicts an efficiency curve versus velocity ratio for a reaction-type expander. The optimum efficiency will occur at a velocity ratio of. 63. For a velocity ratio considerable greater or less than. 63 a significant efficiency penalty can be expected. Considering the effects on the parameters mentioned above, it is easy to see the importance the velocity ratio has on the performance of the expander.  [c.224]

The two types of turbines—axial-flow and radial-inflow turbines—can be divided further into impulse or reaction type units. Impulse turbines take their entire enthalpy drop through the nozzles, while the reaction turbine takes a partial drop through both the nozzles and the impeller blades.  [c.44]

The two types of turbines—axial-flow and radial-inflow turbines—can be divided further into impulse or reaction type units. Impulse turbines take their entire enthalpy drop through the nozzles, while the reaction turbine takes a partial drop through both the nozzles and the impeller blades.  [c.132]

Figure 9-10. Schematic of a reaction-type turbine showing the distribution of the thermodynamic and fluid mechanic properties. Figure 9-10. Schematic of a reaction-type turbine showing the distribution of the thermodynamic and fluid mechanic properties.
Several processes are unique to ions. A common reaction type in which no chemical rearrangement occurs but rather an electron is transferred to a positive ion or from a negative ion is tenued charge transfer or electron transfer. Proton transfer is also conunon in both positive and negative ion reactions. Many proton- and electron-transfer reactions occur at or near the collision rate [72]. A reaction pertaining only to negative ions is associative detaclunent [73, 74],  [c.806]

Gelemter and Rose [25] used machine learning techniques Chapter IX, Section 1.1 of the Handbook) to analyze the reaction center. Based on the functionalities attached to the reaction center, the method of conceptual clustering derived the features a reaction needed to possess for it to be assigned to a certain reaction type. A drawback of this approach was that it only used topological features, the functional groups at the reaction center, and its immediate environment, and did not consider the physicochemical effects which are so important for determining a reaction mechanism and thus a reaction type.  [c.192]

A functional group can, however, have different effects, depending on the mechanism of a reaction type and depending on the electron demand on the reaction center. Thus, Figure 3-18 shows how functional groups can be considered as either electron-donating or radical-stabilizing (e.g., OR), or as either radical-stabilizing or electron-withdrawing (e.g., CN). Furthermore, whereas in many reactions a -P0(0R)2 group is electron-withdrawing such as the -CHO, -COOR, -CN, or -SO2R groups, yet the Wittig-Horner reaction needs a -PO(OR)2 group at a carbon atom and none of the other groups in this list can initiate a Wittig-Homer reaction. Thus, neither an unequivocal classification nor a universal generalization of functional groups is possible.  [c.192]

Sending the entire dataset through this network leads to a distribution of the I 20 reactions acro.ss the 2D arrangement of neurons. The question is now, doe.s this distribution make sense Remember we have used an unsupeiwised learning method and therefore have not said anything about the membership of a reaction in a certain reaction type. In order to analyze the mapping, these 120 reactions were classified intellectually by a chemist and the neurons were patterned aecord-ing to the assignment of a reaction to a certain type (this was done a posteriori, after training of the network we still have unsupervised learning ). Figure 3-20a shows the map thus patterned. It can be seen that reactions considered by a chemist to belong to one and the same reaction type arc to be found in contiguous parts of the Kolionen map. This becomes even dearei when we pattern the empty neurons, those neurons that did not obtain a reaction, on the basis of their k nearest neighbors a neuron obtains a pattern by a majority decision of its nearest neighbors (figure 3-2Db.  [c.195]

There are finer details to be extracted from such Kohonen maps that directly reflect chemical information, and have chemical significance. A more extensive discussion of the chemical implications of the mapping of the entire dataset can be found in the original publication [28]. Gearly, such a map can now be used for the assignment of a reaction to a certain reaction type. Calculating the physicochemical descriptors of a reaction allows it to be input into this trained Kohonen network. If this reaction is mapped, say, in the area of Friedel-Crafts reactions, it can safely be classified as a feasible Friedel-Qafts reaction.  [c.196]

The hydrophobic constant r is a measure of the contribution of a substituent X to the lipophilidty of compound R-X compared with R-H. The constant representing the solvent/solvent system, analogously to Hammett s p constant for the reaction type, was arbitrarily set to 1 for octanol/water and thus does not appear in Eq. (7). The lipophilidty constant ti allows the estimation of log P values for congeneric series of compounds with various substituents (see Eq. (8)).  [c.492]

No evaluation This allows the exhaustive generation of all conceivable reaction pathways. For example, starting with n-octanc, all isomeric CK-alkancs can be generated by a reaction type that involves the breaking and making of a C-C and a C-H bond (Figure 10.3-9).  [c.551]

The breaking of a strategic bond and the generation of synthesis precursors defines a synthesis reaction. In the simplest case, the reaction is already known from literature. In most cases, however, the rcaaion step obtained has to be generalised in order to find any similar and successfully performed reactions with a similar substituent pattern or with a similar rearrangement of bonds. One way of generalizing a reaction is to identify the reaction center and the reaction substructure of the reaction. This defines a reaction type.  [c.571]

Section 8 1 Nucleophilic substitution is an important reaction type m synthetic organic chemistry because it is one of the mam methods for functional group transformations Examples of synthetically useful nucleophilic sub stitutions were given m Table 8 1 It is a good idea to return to that table and review its entries now that the details of nucleophilic substitution have been covered  [c.355]

You will recognize the side chain oxidation of p xylene to terephthahc acid as a reaction type discussed previously (Section 11 13) Examples of other reactions encoun tered earlier that can be applied to the synthesis of carboxylic acids are collected m Table 19 4  [c.806]

A special cryogenic reactor (35) in which the reactions of fluorine with Hquid and gaseous samples can be controlled at very low temperatures is shown ia Figure 5. Reactants are volatilized iato the reaction zone of the cryogenic reactor from the heated oil evaporator prior to initiation of the reaction. The main reaction chamber is a nickel tube, 2.54 cm ia diameter, packed with copper turnings. The compartments (10.1 x 10.1 x 20.2 cm) are constmcted of stainless steel and iasulated with urethane foam and act as heat sinks. AH connections are made of 0.635 cm copper or aluminum tubiag. A sodium fluoride trap is used to remove the hydrogen fluoride from the reaction products. By cooling or warming the compartments, they can be used to create a temperature gradient along the reaction tube. Because the products are highly fluoriaated, they are usually volatile and tend to move through the reactor tube rapidly, depending on the temperature gradient. This provides a continually renewed surface of reactant at the optimum temperature for fluotination. Fluoriaated copper turnings effectively iacrease the surface area of the compound exposed to fluotine. The iadividual zones of the reactor maybe cooled with various solvent—soHd carbon dioxide or with solvent—Hquid nitrogen slushes. Preferably, the temperature is precisely regulated with an automatic Hquid nitrogen temperature controHer. In addition to the four-zone reactor shown ia Figure 5, a multizone reactor can also be used an eight-zone reactor has been found to be particularly efficient (36). Internal Freon cooling is effective for controlling the temperatures of the various compartments (37).  [c.277]

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%.  [c.455]

For example, a secondary alcohol of an average molecular weight of 202, containing 12—14 carbon atoms, is introduced into a reaction tube packed with a cobalt promoted zirconium catalyst on alumina at a rate of 60 mL /h along with Hquid ammonia (90 mL /h) and hydrogen (5 L/h) to produce an amine mixture composed of 92.2% primary amine, 2.15% secondary and tertiary amines, and 5.7% unreacted alcohol (52). The reaction, at 180—190°C and 24 MPa ( ii3500 psig), is mn by withdrawing the Hquid reaction product from the bottom of the reactor.  [c.220]

Reaction-Type Crystallizers In chemical reactions in which the end product is a soUd-phase material such as a crystal or an amorphous solid the type of equipment described in the preceding subsections or shown in Fig. 18-68 may be used. By mixing the reactants in a large circulated stream of mother liquor containing suspended soUds of the equihbiium phase, it is possible to minimize the driving force created during their reaction and remove the heat of reaction through the vaporization of a solvent, normaUy water. Depending on the final paiticfe size required, it is possible to incorporate a fines-destruciion baffle as shown in Fig. 18-68 and take advantage of the control over particle size afforded by this technique. In the case of ammonium sulfate crystaUization from ammonia gas and concentrated sulfuric acid, it is necessary to vaporize water to remove the heat of reaction, and this water so removed can be reinjected after condensation into the fines-destruction stream to afford a very large amount of dissolving capabihty.  [c.1665]

An impulse-type turbine experiences its entire enthalphy drop in the nozzle, thus naving a very high velocity entering the rotor. The velocity entering the rotor is about twice the velocity of the wheel. The reaction type turbine divides the enthalphy drop in the nozzle and in the rotor. Thus, for example, a 50 percent reaction turbine has a velocity leaving the nozzle equal to the wheel speed and produces about V2 the work of a similar size impulse turbine at about 2-3 percentage points higher efficiency than the impulse turbine (0 percent reaction turbine). The effect on the efficiency and ratio of the wheel speed to inlet velocity is shown in Fig. 29-27 for an impiilse turbine and 50 percent reaction turbine.  [c.2510]


See pages that mention the term Nef reaction TFaP : [c.170]    [c.551]    [c.551]    [c.557]    [c.61]    [c.303]    [c.478]    [c.330]    [c.50]    [c.119]    [c.1320]    [c.2510]    [c.2511]   
The nitro group in organic synthesis (2001) -- [ c.162 ]