Parent Structures

In such tables, typical chemical shifts are assigned to standard structure fragments (e.g., protons in a benzene ring). Substituents in these blocks (e.g., substituents in ortho, meta, or para positions) are assumed to make independent additive contributions to the chemical shift. These additive contributions are listed in a second series of tables. Once the tables are defined, the method is easy to implement, does not require databases, and is extremely fast. Predictions for a molecule with 50 atoms can be made in less than a second. On the other hand, it requires that the parent structure and the substituents are tabulated, and it considers no interaction... 

Table 1.12 Parent Structures of Phosphorus-Containing Compounds 1.36...

For branching compounds, the parent structure is the longest continuous chain present in the compound. Consider the compound to have been derived from this structure by replacement of hydrogen by various alkyl groups. Arabic number prefixes indicate the carbon to which the alkyl group is attached. Start numbering at whichever end of the parent structure that results in the lowest-numbered locants. The arable prefixes are listed in numerical sequence, separated from each other by commas and from the remainder of the name by a hyphen. 

Phosphorus Compounds. Acyclic phosphorus compounds containing only one phosphorus atom, as well as compounds in which only a single phosphorus atom is in each of several functional groups, are named as derivatives of the parent structures listed in Table 1.12. Often these... 

Table 2. Compounds Used as Parent Structures with Trivial Names...

The need for simple names to describe complex structures has been met in several ways, the most straightforward of which is to use a trivial name giving little or no structural information e.g. morphine, opuntiol). Such names are.often based on the Latin name of the species from which the compound was isolated e.g. opuntiol from Opuntia eliator). While this is acceptable for a newly isolated compound of unknown structure, it is less satisfactory once the structure is established. What is needed is some means of establishing the relationship of the compound to others in the same class, without going into too much detail with regard to structure and stereochemistry. This can be achieved by defining, for a particular group of structures, a parent structure. 

Most parent structures consist essentially of an assembly of rings and/or chains, the degree of hydrogenation of which is defined (usually completely saturated or containing the maximum number of non-cumulative double bonds in cyclic portions), and having no attached functional substituents (the carbohydrates are a notable exception to this). The stereochemistry at all (or most) chiral centres is defined thus such parent structures are sometimes referred to as stereoparents . Some examples are shown (77)-(83). 

As mentioned above, it is usually most convenient to employ as parent structure a skeleton from which all functional substituents have been removed. However, there are many substituted parent names in common use, either with or without implied stereochemistry (see examples 102-106). 

Concerning nomenclature, fulvalene 2 and its related systems 1 and 3-6 are the parent structures of this class of heterocyclic cross-conjugated compounds. Both ring systems are numbered as shown in formula 9 (1,4,5,8-tetraazafulva-lene) beginning at the heteroatoms. Alternatively, as in the case of heptafulva-lene 10 (3,3 -diazaheptafulvalene), the numbers 1-7 and l -7 can be used.Tlie use of the name of the parent heterocycle connected by an olefinic double bond is often favored for the nomenclature of electron-rich olefines, for example, bis[3-(2,6-diisopropylphenyl)-4,5-dimethylthiazol-2-ylidene] for compound 51a (97LAR365). Similarly, azafulvalenes of type 11 and 12 can be re-... 

Hydrocarbons containing both aliphatic and alicyclic parts may be named by considering either part as the parent structure and the other part as a substituent, e.g.. 

Aromatic groups are called aryl groups if they are attached directly to a parent structure. Common aryl groups are... 

The versatility of poly(phenylcne) chemistry can also be seen in that it constitutes a platform for the design of other conjugated polymers with aromatic building blocks. Thus, one can proceed from 1,4- to 1,3-, and 1,2-phenylene compounds, and the benzene block can also be replaced by other aromatic cores such as naphthalene or anthracene, helerocyclcs such as thiophene or pyridine as well as by their substituted or bridged derivatives. Conceptually, poly(pheny ene)s can also be regarded as the parent structure of a series of related polymers which arc obtained not by linking the phenylene units directly, but by incorporation of other conjugated, e.g. olefinic or acetylenic, moieties. 

Numbering and naming of the parent structure 2-Carb-3. The Fischer projection of the acyclic form 2-Carb-4. Configurational symbols and prefixes... 

Carb-2. Parent monosaccharides 2-Carb-2.1. Choice of parent structure... 

In cases where more than one monosaccharide structure is embedded in a larger molecule, a parent structure is chosen on the basis of the following criteria, applied in the order given until a decision is reached ... 

When the parent structure is symmetrical, preference between alternative names for derivatives should be given according to the following criteria, taken in order ... 

Fischer projection of acyclic form, 56-57 glycosides, 132-135 C-glycosyl compounds, 139-140 N-glycosyl derivatives, 137-139 glycosyl halides, 136-137 glycosyl residues, 125 isotopic substitution and isotopic labelling, 91 me so forms, 59 optical rotation, 59 parent structure choice, 53... 

The advantages of SIMS are its high sensitivity (detection limit of ppms for certain elements), its ability to detect hydrogen and the emission of molecular fragments that often bear tractable relationships with the parent structure on the surface. Disadvantages are that secondary ion formation is a poorly understood phenomenon and that quantification is often difficult. A major drawback is the matrix effect secondary ion yields of one element can vary tremendously with chemical environment. This matrix effect and the elemental sensitivity variation of five orders of magmtude across the periodic table make quantitative interpretation of SIMS spectra oftechmcal catalysts extremely difficult. 

One of the typical black developing fluoran compounds is 2 -anilino-6 -diethylamino-3 -methylfluoran (50)6 in which the methyl group at 3 -position plays a very important role. The parent structure of 50 is 2 -anilino-6 -... 

Improvement of the properties of a drug may be achieved by the chemical modification of the parent drug. The preparation of an ester, salt, or other modification of the parent structure may be employed with parenteral drugs to increase stability, alter drug solubility, enhance depot action, avoid formulation... 

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