Other types of substitutions

Diaring the last decade a large amount of nucleophilic addition and substitution reactions have been performed in water alone or in monophasic water/organic solvent systems. The yields obtained, as well as the diastereo- and enantioselectivities, are often as high, and sometimes even better, than those obtained in traditional organic solvents. Sometimes completely new reactivities can be discovered using water as the solvent. Moreover, the substitution of common organic solvents by water should be of real benefit to our health and environment. 

Fringuelli, R, Pani, G., Piermatti, 0. and Pizzo, R, Condensation reactions in water of active methylene compounds with arylaldehydes, Tetrahedron, 1994, 50, 11499-11508. 

and Wang, G.-W., Efficient and clean aldol condensation catalyzed by sodium carbonate in water, Chem. Lett., 2003,32, 966-967. 

Tanemura, K., Suzuki, T., Nishida, Y. and Horaguchi, T., Aldol condensation in water using polyethylene glycol 400, Chem. Lett., 2005, 34, 576-577. 

Saimoto, H., Onitsuka, T., Motobe, H., Okabe, S., Takamori, Y, Morimoto, M. and Shigemasa, Y., Reactions of C3 and C4 ketoses with alkenals and alkenones in water. Tetrahedron Lett., 2004, 45, 8777-8780. 

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When isotopic substitution creates a centre of chirality, configuration is defined as for other types of substitution (see 2-Carb-16.1 to 2-Carb-16.4). 

R = R = Me), vinyl chlorides (77), and thioesters (78), as shown in Scheme 5. ° Methyl methylthiomethyl sulphoxide anion has been used to make 2-arylpropanoate esters and 1,4-diketone precursors, while other types of substituted cr-sulphinyl carbanions have been utilized in the preparation of... 

For mono-, meta-, and 1,3,5-trisubstitnted benzenes, this is an excellent Raman group frequency. It always occurs at 1010 10 cm and is always one of the strongest bands. For other types of substitution it is not usefnl. 

Other types of substitution such as 1,2, 1,3, 1,3,5, etc., give rise to coupled modes with both vea and veb and therefore do not generate good group frequencies. 

Aromatization of indolines is important in completing synthetic sequences in which the directive effects of the indoline ring have been used to achieve selective carbocyclic substitution[l]. Several methods for aromatization have been developed and some of these are illustrated in Table 15.2. A range of reagents is represented. One type of procedure represents use of oxidants which are known to convert amines to imines. Aromatization then provides the indole. Such reagents must not subsequently oxidize the indole. Mereuric acetate (Entry 1) is known to oxidize other types of amines and presumably reacts by an oxidative deprotonation ot- to the complexed nitrogen. 

The substitution of asbestos fibers by other types of fibers or minerals must, ia principle, comply with three types of criteria (36) the technical feasibihty of the substitution the gain ia the safety of the asbestos-free product relative to the asbestos-containing product and the availabiHty of the substitute audits comparative cost. 

Several types of nitrogen substituents occur in known dye stmetures. The most useful are the acid-substituted alkyl N-substituents such as sulfopropyl, which provide desirable solubiUty and adsorption characteristics for practical cyanine and merocyanine sensitizers. Patents in this area are numerous. Other types of substituents include N-aryl groups, heterocycHc substituents, and complexes of dye bases with metal ions (iridium, platinum, zinc, copper, nickel). Heteroatom substituents directly bonded to nitrogen (N—O, N—NR2, N—OR) provide photochemically reactive dyes. 

Other technique—for example, dynamic secondary ion mass spectrometry or forward recoil spectrometry—that rely on mass differences can use the same type of substitution to provide contrast. However, for hydrocarbon materials these methods attain a depth resolution of approximately 13 nm and 80 nm, respectively. For many problems in complex fluids and in polymers this resolution is too poor to extract critical information. Consequently, neutron reflectivity substantially extends the depth resolution capabilities of these methods and has led, in recent years, to key information not accessible by the other techniques. 

Reactions offluorinated dipoles. In recent years, much effort has been devoted to the preparation of tnfluoromethyl-substituted 1,3-dipoles with the goal of using them to introduce trifluoromethyl groups into five-membered nng heterocycles Fluorinated diazoalkanes were the first such 1,3-dipoles to be prepared and used in synthesis A number of reports of cycloadditions of mono- and bis(tnfluo-romethyl)diazomethane appeared prior to 1972 [9] Other types of fluonne-substi-tuted 1,3-dipoles were virtually unknown until only recently However, largely because of the efforts of Tanaka s group, a broad knowledge of the chemistry of tnfluoromethyl-substituted nitrile oxides, nitnle imines, nitnle ylides, and nitrones has been accumulated recently... 

Since then, the metathesis reaction has been extended to other types of alkenes, viz. substituted alkenes, dienes and polyenes, and to alkynes. Of special interest is the metathesis of cycloalkenes. This gives rise to a ring enlargement resulting in macrocyclic compounds and eventually poly-... 

Two other types of host for arenediazonium salts were found by Shinkai et al., the calix[ ]arenes, 11.10 (1987 a, 1987 b) and 11.11 (1988). The hexasulfonated calix[6]arenes 11.10 suppress dediazoniation of substituted benzenediazonium ions in aqueous solution much more efficiently than 18-crown-6. The complexation of calix[ ]arenes 11.11 (n = 4, 6, and 8) with 4 -dimethylaminoazobenzene-4-diazonium ions (11.12) was measured, and was found to be weaker than that of 18-crown-6. It may be that the large difference in behavior between these two types of complexation reagents 11.10 and 11.11 is due to the significantly different diazonium ions used as guests for the two types. Electronically the azobenzenediazonium ion (11.12) is... 

If, instead of a palladium catalyst, a nickel catalyst, such as the bipyridylnickel(II) bromide, is used for the arylation of amines (Fig. 7), the reduction of the aryl halide into the corresponding aromatic hydrocarbon is still present for the primary or secondary benzylamines but, the arylation into substituted anilines is the main reaction even most often the only one, for the other types of amines. 

In the last chapter we saw the importance of nnderstanding mechanisms. We said that mechanisms are the keys to understanding everything else. In this chapter, we wiU see a very special case of this. Students often have difficulty with substitution reactions—specifically, being able to predict whether a reaction is an Sn2 or an SnI. These are different types of substitution reactions and their mechanisms are very different from each other. By focusing on the differences in their mechaiusms, we can understand why we get Sn2 in some cases and SnI in other cases. 

Other types of deformation may be handled similarly. Shear, for example, may be treated as a homogeneous strain involving an increase in one coordinate x) while another (z) remains constant, the volume being constant also. Thus, we may let aa = a, oLy = a, and az=. On substitution of these conditions in Eq. (41), the deformation entropy per unit volume becomes... 

At room temperature under photostimulation a-nitrosulfones react with a variety of nucleophiles via radical anion chain reactions interestingly, in none of the cases where the PhSOj group is involved in SrnI type of substitution does the O end of the ambident anion " play a role. This strong regioselectivity is reminiscent of the one reported for other ambident anions involved in these radical chain substitutions. ... 

The classifier described above works very well with coarse particles where exact splits are not needed. Typical applications are in connection with ball or rod mills for reduction to particle sizes between 8- and 20-mesh. These classifiers have high capacities they lift coarse solids for return to the mill, so that auxiliary conveyors and elevators are not required. There are other types of classifier that must be usual for close separations with fine particles. One such device is the centrifugal classifier its action bears a strong resemblance to that of the crossflow classifier, but the settling is greatly accelerated by the substitution of centrifugal force for gravitational force. 

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