Substitutions, types

Another quantitative approach to the reactivity of thiazole (381) in reactions involving a cationic transition state, though not exactly of the electrophilic substitution type, deserves to be mentioned here because of... 

An intramolecular Diels-Alder cyclization produces excellent yields of 2-aminoquinoline-3-carboxylate esters (57). Equally fine yields of the requited carbodiimides have been reported, making this an attractive route to an unusual substitution type. 

Table 2. Structure Types, Boron Coordination and Representatives of Metal Borides (Substitutional Types and CaCu5 Structure Family)... 

Between all the classes of substituted phosphinous amides summarized in Table 1, those with the P atom totally substituted are more stable than others with H-P bonds, as in many other classes of organophosphorus compounds. Between those, the trisubstituted or fully substituted (typed in boldface) are by far the most stable and the main actors of the chemistry described in the following pages. 

We are now prepared to develop quantitative relations for series-parallel reactions of the multiple substitution type considered above. 

The proton affinities (PA) of two restricted subsets of amines were correlated directly with inductive and polarizability effect parameters, respectively (Figs. 19 and 22). These can be combined with data on other hetero-substituted amines to give a set of 80 amines of different skeletal and substitution types (e.g. Fig. 24). In this and all other systems (below), a residual electronegativity value, %l2, (Eq. 5) derived from those of the atoms of the first, 1, and second, 2, sphere neighbors of the nitrogen atom is preferred as a measure of the inductive effect49). 

Substitutional ring openings seem to be more unusual (Eqs. 22-24, Scheme 5). The reactions of 2,5-dimethoxyselenophene with butyl- and phenyllithium have been examined.85 In view of the formation of dibutyl-and diphenylselenide, respectively, together with some dienes, a logical reaction sequence could be formulated in which the first step is an attack on the selenium atom by the lithium reagent. Nonfused selenophenes are also cleaved in a substitution-type reaction. 

Reaction of the conjugate base of diethyl phosphite with 3-car-boxyethyl-substituted 2,5-halomethylfurans provided interesting products as alternatives to the normally anticipated Michaelis-Becker substitution-type products.452 Rather than simple substitution, overall reduction of the halomethyl linkage(s) to methyl(s) were observed with a Michael-type addition of phosphorus to the 4-position of the ring. 

In the provisions section, you can put any model to which the substituted types must already conform.6 Thus, you can require that one substituted type be a subtype of another or that they have some relationship (see Section 9.2.1, Framework Applications Are Not Subtypes) or satisfy some predicate. The designer who applies the template must check, perhaps with help from a tool, that all the other parts of his or her model imply the properties laid down as provisions, and this should be documented much as a refinement is documented. 

In general, we do not constrain the types that can be substituted, because we sometimes substitute just to avoid name clashes between multiple imports (see Figure 9.35). The markers simply suggest places for substitution but unmarked types can be substituted, and marked types can be left unsubstituted. Any substitutable type that isn t substituted when imported remains as a substitutable type in the importer. 

Substitute type Fterson, and attribute ss sterotype can take additional textual substitutions ... 

During the course of the nineteenth century, organic chemists developed a complex and integrated theory of chemical identity and constitution that in eluded theories of chemical atoms and equivalents, radicals, substitution, types, and valence, eventually unified in the so-called structure theory of constitutional formulas. But by midcentury, there was some discontent among chemists about the limitations of the overall theoretical framework within which they were working. 

In bacterial systems, 1,2-dibromoethane is a direct-acting mutagen and primarily causes mutations of the base-pair substitution type (Barber et al. 1981 McCann et al. 1975 Moriya et al. 1983 ... 

First-order reaction kinetics is frequently observed in organic chemistry in the form of an SnI reaction, indicating it is a first-order nucleophilic substitution type. An example is the solvolysis of tcrt-butylbromide at alkaline pH to form t rt-butanol and bromide ion. The reaction probably proceeds in two steps ... 

Substitution (type nucleophilic) reactions in which an electron-rich agent (or nucleophile) attacks and forms a transient or stable bond with an electron-poor center (often carbon or phosphorus in biological systems) which has undergone prior or simultaneous expulsion of the leaving group (or exiphile). 

The IR spectra are useful for detecting functional groups of Aristolochia alkaloids. Aristolochic acids show two characteristic bands at 1550 and 1350 cm due to the absorption of nitro group, and the carboxy OH group appears at 3000-2500 cm as a broad continuous absorption. Hydroxy derivatives of aristolochic acids or aristolactams show OH and NH absorptions at 3300-3500 and 3200-3400 cm The carboxy or lactam carbonyl is present at 1690 cm i. In general, the aromatic ring system shows stretches at 1625-1575 and 1525-1475 cm 1 as usual, and observation of the 900-700 cm region is often used for analysis of substitution type in aromatic derivatives 28). 

Nitration reactions are mostly substitution type, forming a wide variety of products including nitrobenzene, nitrotoluenes, nitroglycerine, nitrocellulose, trinitrotoluene, nitrophenols and nitroparaffins, many of which are known chemical explosives. Some examples are ... 

Annelation on to a benzene ring increases considerably the complexity of the spectra, and indole has absorptions at 216 (4.54), 266 sh (3.76), 270 (3.77), 276 (3.76), 278 (3.76) and 287 (3.68) nm in ethanol solution. Because of the widespread occurrence of the indole ring system in nature and the sensitivity of absorption band position and intensity to substitution type, considerable use has been made of electronic spectroscopy in the past for structure identification. An extensive tabulation of data, primarily for monosubstituted derivatives, is available (71PMH(3)67,p.94). As expected, whereas the effects of alkylation are comparatively slight, introduction of groups capable of mesomeric interaction with the indole it -system may cause profound changes in the appearance of the spectrum representative examples are given in Table 24. 

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