Heteroatoms defined

By contrast base-catalyzed mechanisms are generally fast, provided, of course, that one of the heteroatoms defining the tetrahedral intermediate has an ionizable proton. 

The number of groups attached directly to the heteroatom defines its CN, and examples of CN-3 and -4 were discussed above. In this section, structurally different examples of CN-4, -5, and -6 are illustrated. Arsoles form the As adducts (22) and (23) with halogens and hypochlorites, respectively. The chlorostibole (24) is converted into the hexavalent anion (25). Spirocyclic deriva-... 

An ylide can be defined as a compound in which a carb-anion is attached directly to a heteroatom carrying a high degree of positive charge ... 

In the cases 6-R-3-Y and 5-R-2-Y, the relation of R to Y corresponds to the para relation in benzene. When Y is in the 4-position, only meta-type (2-R or 6-R) substituents are possible. With R in the 2-position, aside from the one para-type relation (5-R-2-Y), two different metatype relations (4-R- and 6-R-2-Y) are possible, and the reactivity need not be the same for these two. Two ways suggest themselves to overcome this difficulty One might attempt to define separate a-values for substituents, depending not only on the relative position with respect to the side-chain, as in and Op, but also in relation to the heteroatom ... 

The alternate procedure, which has actually been applied, is to define separate reaction constants p, pp, and py), depending on the location of the side-chain relative to the heteroatom, and to make separate correlations. Here, the remaining uncertainty is that for 2-Y there are the two meta-type positions mentioned above. This is the approach which has been used successfully in the few reported correlations to be discussed below. 

There exist many types of azoloquinolines, and therefore it is necessary to define the objects of interest to be described in this review. The tricyclic azoloquinolines reviewed in this article have an azole ring fused to the benzene ring of quinoline (not isoquinoline derivatives) in positions / g, and h. This means that the benzene ring is between azole and pyridine rings, and all of them are ortho-peri condensed. The azole and benzene rings do not have a common heteroatom, and also a carbon... 

The ylides may be defined as dipolar compounds in which a carbanion is covalently bonded to a positively charged heteroatom. They are represented by the following general formula ... 

The variants are distinguished by the locants of those ring atoms that lie outside a reference plane (defined below) and are listed for some examples in Table 1. The locants of ring atoms that lie on the side of the reference plane from which numbering appears clockwise (i.e. the upper side in the normal Haworth representation of furanoses and pyranoses) are written as superscripts and precede the letter those that lie on the other side are written as subscripts and follow the letter. Heteroatoms (e.g. O, S) are indicated by their subscript or superscript atomic symbols. Table 1 gives the notations and Chart III some examples. 

Step 1. ICs are defined as any carbons containing no double or triple bonds to heteroatoms. ICs isolate functional groups from each other according to the classical Hammett concept, so that the treatment of complex structures is simple. 

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

The stability of heteroatom-centered radicals can be defined relative to reference systems sharing the same type of radical center. The stability of nitrogen-centered radicals may, for example, be defined relative to ammonia... 

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