First Examples

At one sampling point near the Technical University of Kosice (Slovakia) (see Fig. 7-13) sedimented airborne particulate matter was sampled by the above described BER-GERHOFF method (see also Section 7.2.1.1) over a period of two and a half years. Tab. 7-5 shows the analytical methods applied for the determination of the elemental composition of the dust samples. 

Differential pulse anodic stripping voltammetry Pb, Zn (in lower concentration) 

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The first example presents the importance of the impulse response function for the comparison of several sensors with the same arrangement from chapter 3.1.. 

A first example of application of microtomography is taken from life sciences. Here X-ray microscopy and microtomography allows to reconstruct the internal three-dimensional microstructure without any preparation and sometimes even of living objects. Fig. la shows an X-ray transmission microscopical image of bone (femoral head). Several reconstructed cross-sections are shown in Fig.lb. Fig.lc shows the three-dimensional reconstruction of this bone. 

The first example refers to the detection of a 1mm side drilled hole at a depth of 45 mm in a polyethylene plastic material. Due to the high sound absorption in plastics, a low operating frequency is chosen. A probe having a 1 MHz element of 24 mm diameter was selected for this example. The echo pattern of a conventional probe with a PZT transducer is pre-... 

The first example refers to the inspection of turbine blades Customers ask for a system which... 

Classically, the nuclei vibrate in die potential V(R), much like two steel balls coimected by a spring which is stretched or compressed and then allowed to vibrate freely. This vibration along the nuclear coordinated is our first example of internal molecular motion. Most of the rest of this section is concerned with different aspects of molecular vibrations in increasingly complicated sittiations. 

Our first example of aP - signal is coherent anti-Stokes Raman spectroscopy, or CARS. Fomially, tire emission signal into direction k= - k + k. has 48 Feynman diagrams that contribute. Flowever, if the... 

Onsager s solution to the 2D Ising model in zero field (H= 0) is one of the most celebrated results in theoretical chemistry [105] it is the first example of critical exponents. Also, the solution for the Ising model can be mapped onto the lattice gas, binary alloy and a host of other systems that have Hamiltonians that are isomorphic to the Ising model Hamiltonian. 

This tutorial, which is based on the Beilstein update BS0202PR (May, 2002) and on the retrieval program Cro.ssFire Commander V6,. shows. some typical advanced search examples in the Beilstein database. It is assumed that the user already knows some of the basic features of the retrieval program. Moreover, in this tutorial the CrossFire Structure Editor is used instead of the (SIS/Draw Structure Editor. The first example is a combined application of structure aiM fact retrieval, whereas the second example demonstrates reaction retrieval. 

The aim of the first example is to look for polychlorinated biphenyls (PCB) for which C-NMR spectra, measured in deuterochloroform, as well as the partition coefficients between 1-octanol and water arc known. Since it is not reliable to per-... 

After return to the Commander window, the reaction retrieval may be executed separately 629 Dicls-Aldcr reactions between aliphatic dienes and cyclic dicno-pliiles are found. This partial result can be narrowed down by restricting tlie reaction conditions by means of the fact editor, The search field codes for the yield and the temperature can be found to be RX.NYD and RX.T, respectively, either by browsing the database structure or by applying the Find option, as described in the first example. To ensure that the retrieved reaction conditions belong to the same experiment, both search terms must be connected by means of the PROXIMITY operator. Before the retrieval is started, the option "Refine results in... 

In this section, the basic concepts of reaction retrieval are explained. The first example is concerned with finding an efficient way to reduce a 3-methy]cydohex-2-cnonc derivative to the corresponding 3-mcthylcyclohcx-2-cnol compound (see Figure 5-24). As this is a conventional organic reaction, the CIRX database should contain valuable information on how to syntbesi2e this product easily. 

The aim of the second example is to find suitable reaction conditions for running the same reduction reaction as in the first example, but in the presence of another carbonyl group which should not react. Furthermore, the reaction should lead to a product with a yield of 80% or more and a specific stereochemical configuration. 

By applying the BROAD classification feature to the hit list of the first example, described in Section 5.13.2, 18 clusters arc found, llic second reaction instance of the first cluster is shown in figure 5-30. 

Figure 10.3-20 shows that i-glutamate plays an important role in the metabolism with many reactions leading to this compound and many reactions starting from it. The first example gives a full structure search in order to show how easy it is to find all reactions that a certain compound participates in. 

To our knowledge, the results presented in this chapter provide the first example of enantioselective Lewis-acid catalysis of an organic reaction in water. This discovery opens the possibility of employing the knowledge and techniques from aqueous coordination chemistry in enantioselective catalysis. This work represents an interface of two disciplines hitherto not strongly connected. 

The first example of enantioselective catalysis of a Diels-Alder reaction was reported in 1979 . Since then, an extensive set of successful chiral Lewis-acid catalysts has been prepared. Some selected examples will be presented here together with their mechanistic interpretation. For a more complete... 

In Chapter 2 the Diels-Alder reaction between substituted 3-phenyl-l-(2-pyridyl)-2-propene-l-ones (3.8a-g) and cyclopentadiene (3.9) was described. It was demonstrated that Lewis-acid catalysis of this reaction can lead to impressive accelerations, particularly in aqueous media. In this chapter the effects of ligands attached to the catalyst are described. Ligand effects on the kinetics of the Diels-Alder reaction can be separated into influences on the equilibrium constant for binding of the dienoplule to the catalyst (K ) as well as influences on the rate constant for reaction of the complex with cyclopentadiene (kc-ad (Scheme 3.5). Also the influence of ligands on the endo-exo selectivity are examined. Finally, and perhaps most interestingly, studies aimed at enantioselective catalysis are presented, resulting in the first example of enantioselective Lewis-acid catalysis of an organic transformation in water. 

To the best of our knowledge the data in Table 3.2 constitute the first example of enantio selectivity in a chiral Lewis-acid catalysed organic transformation in aqueous solution. Note that for the majority of enantioselective Lewis-acid catalysed reactions, all traces of water have to be removed from the... 

One example has already been encountered in the form of the binding constants in Table 3.2. These data form one of the first examples of compelling evidence for the involvement of attractive arene -arene interactions in determining the outcome of enantioselective catalysis. These attractive interactions have been frequently invoked as explanations for the observed enantioselectivities of... 

In articles like this one, the scientists don t have the time nor the space to write out the details and amounts of reactants used for every single substrate they tried things on. So they pick just a few of the precursors they tried and use their numbers as an example of how the reaction typically goes. All one does is just substitute an equal amount of their favorite phenylacetone for the one in the example while keeping everything else the same. This will not be too big of a stretch of the old imagination with the first example below. The example ketone is just phenylbutanone. One little carbon more than phenylacetone, but a methyl ketone nonetheless (don t ask). They react exactly the same. As it so happens this first example is also the one using ammonium acetate to make MDA. Sweet ... 

The large sulfur atom is a preferred reaction site in synthetic intermediates to introduce chirality into a carbon compound. Thermal equilibrations of chiral sulfoxides are slow, and parbanions with lithium or sodium as counterions on a chiral carbon atom adjacent to a sulfoxide group maintain their chirality. The benzylic proton of chiral sulfoxides is removed stereoselectively by strong bases. The largest groups prefer the anti conformation, e.g. phenyl and oxygen in the first example, phenyl and rert-butyl in the second. Deprotonation occurs at the methylene group on the least hindered site adjacent to the unshared electron pair of the sulfur atom (R.R. Fraser, 1972 F. Montanari, 1975). 

A classical way to achieve regioselectivity in an (a -i- d -reaction is to start with a-carbanions of carboxylic acid derivatives and electrophilic ketones. Most successful are condensations with 1,3-dicarbonyl carbanions, e.g. with malonic acid derivatives, since they can be produced at low pH, where ketones do not enolize. Succinic acid derivatives can also be de-protonated and added to ketones (Stobbe condensation). In the first example given below a Dieckmann condensation on a nitrile follows a Stobbe condensation, and selectivity is dictated by the tricyclic educt neither the nitrile group nor the ketone is enolizable (W.S. Johnson, 1945, 1947). 

Out first example is 2-hydroxy-2-methyl-3-octanone. 3-Octanone can be purchased, but it would be difficult to differentiate the two activated methylene groups in alkylation and oxidation reactions. Usual syntheses of acyloins are based upon addition of terminal alkynes to ketones (disconnection 1 see p. 52). For syntheses of unsymmetrical 1,2-difunctional compounds it is often advisable to look also for reactive starting materials, which do already contain the right substitution pattern. In the present case it turns out that 3-hydroxy-3-methyl-2-butanone is an inexpensive commercial product. This molecule dictates disconnection 3. Another practical synthesis starts with acetone cyanohydrin and pentylmagnesium bromide (disconnection 2). Many 1,2-difunctional compounds are accessible via oxidation of C—C multiple bonds. In this case the target molecule may be obtained by simple permanganate oxidation of 2-methyl-2-octene, which may be synthesized by Wittig reaction (disconnection 1). 

Facile reaction of a carbon nucleophile with an olefinic bond of COD is the first example of carbon-carbon bond formation by means of Pd. COD forms a stable complex with PdCl2. When this complex 192 is treated with malonate or acetoacetate in ether under heterogeneous conditions at room temperature in the presence of Na2C03, a facile carbopalladation takes place to give the new complex 193, formed by the introduction of malonate to COD. The complex has TT-olefin and cr-Pd bonds. By the treatment of the new complex 193 with a base, the malonate carbanion attacks the cr-Pd—C bond, affording the bicy-clo[6.1,0]-nonane 194. The complex also reacts with another molecule of malonate which attacks the rr-olefin bond to give the bicyclo[3.3.0]octane 195 by a transannulation reaction[l2.191]. The formation of 194 involves the novel cyclopropanation reaction of alkenes by nucleophilic attack of two carbanions. 

Recently, an original method of heterocyclization afforded the first examples of 4-arylsulfonylthiazoles (150) (Scheme 77) (358. 359). The... 

The first example of a stereo electronic effect in this text concerned anti elimination in E2 reactions of alkyl halides (Section 5 16)... 

Figure 17 10 presents the mechanism for the reaction between benzaldehyde and methylamine given m the first example The first two steps lead to the carbmolamme the last three show the dehydration of the carbmolamme to the imine Step 4 the key... 

The first example in Table 20 2 mlroduces a new aspecl of nucleophilic acyl sub slilulion lhal applies nol only lo acid anhydrides bul also lo acyl chlorides Ihioeslers esters and amides Nucleophilic acyl subslilulions can be calalyzed by acids... 

In our first example, the stress to the equilibrium was applied directly. It is also possible to apply a concentration stress indirectly. Consider, for example, the following solubility equilibrium involving AgCl... 

Aromatic polyimides are the first example we shall consider of polymers with a rather high degree of backbone ring character. This polymer is exemplified by the condensation product of pyromellitic dianhydride [Vll] and p-amino-aniline [Vlll] ... 

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