Molecular formula, extended

The presence of three methoxyl groups and a phenolic hydroxyl group in corydalmine indicated the extended molecular formula Ci7Hi4N(0Me)30H, and its formulation as a tetrahydroprotoberberine base was suggested from the UV-spectrum X 284 my, log e 3.56). The... 

Extended Molecular Formula (EMF). This search key consists of the molecular formula of each fragment in a compound, qualified by the number of prime rings in that moleform and the number of direct non-hydrogen atoms attached to rings. 

Inquiry Execution. Search execution may be done completely interactively, completely in batch, or partly interactively with completion in batch. All modes of search have a required key search in which the appropriate search index is accessed, the requested NSC numbers are retrieved, followed by an optional iterative search. In GET, this key search involves a simple lookup of the desired NSC numbers. In FSS the hierarchical extended molecular formula (EMF) index is scanned for particular moleforms plus any ring, attachments, and number of fragments specified. In SSS the key expression is analyzed and expanded... 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

PMO materials that are constructed from bis-silylated precursors may be regarded as MCM-41 /SBA-15 phases in which, in the ideal case, a quarter of all Si—O—Si units is replaced by Si—R—Si units, which corresponds to a formal molecular formula of [Ro.sSiOi 5]. Unlike the bivalent oxygen atom, however, the organic bridges can in principle form bonds to more than two silicon atoms. In this way, the structural motifs already realized in PMOs can be extended considerably. At the same time, the mechanical and thermal stability of PMOs may be increased, since tris- and multi-silylated precursors can act as cross-linkers. 

The meaning of a chemical formula was discussed in Chapter 5, and we learned how to interpret formulas in terms of the numbers of atoms of each element per formula unit. In this chapter, we will learn how to calculate the number of grams of each element in any given quantity of a compound from its formula and to do other calculations involving formulas. Formula masses are presented in Section 7.1, and percent composition is considered in Section 7.2. Section 7.3 discusses the mole—the basic chemical quantity of any substance. Moles can be used to count atoms, molecules, or ions and to calculate the mass of any known number of formula units of a substance. Section 7.4 shows how to use relative mass data to determine empirical formulas, and the method is extended to molecular formulas in Section 7.5. 

Two compounds of this type were placed at our disposal isotactic polypropylene and an alternating erythro-iso-copolymer of butene-2 and ethylene. Looking to the extended chemical formula of the latter (Figure 13), it is indeed immediately evident that this copolymer can be considered as an equivalent to a HH polypropylene. The XPS analysis of the valence band spectrum of this compound reveals that its electronic structure, reflected through the C-C (C2s) molecular orbitals is entirely different from that of polypropylene (Figure 14). 

Where ai is the coefficient in the molecular formula for the element i and n is the ionic radius in A. The summation extends to all the elements existing in the zeolite. 

The most simple filters are calculated directly from the molecular formula, from the element composition, or from an extended description of the atom types of a molecule. Extended atom types are notations of atoms that include more information than just the element name (e.g., level of hybridization, membership in a certain functional group, etc.). Many molecular properties are usable as filter descriptors [24-27]. 

Virosecurinine possessed the same molecular formula as securinine and showed no N- or 0-methyl groups. Its IR and UV spectra indicated the presence of an extended a,)5-unsaturated y-lactone moiety. On hydrogenation over palladium in benzene solution, virosecurinine gave dihydrovirosecurinine (109) and an oily aminolactone (110) characterized as its crystalline picrate (mp 215°, dec) and A-acetyl derivative (mp 166-166.5°). Appropriate IR and UV spectra were observed for the two products 109 and 110. Lithium aluminum hydride reduction... 

Just as the atom takes on a significance in learning about chemistry which is not justified in terms of the (lack of) role that discrete atoms play in chemical processes, once learners have been taught about molecules there is a tendency to apply the molecule schema to all structures. The role of valency in limiting, if not exactly determining, molecular formulae, may be extended to metals and to ionic materials. Metals may be seen by students to consist of discrete molecules of similar atoms, in a similar way to iodine or phosphoms. In the ionic case, valency is seen by many students to indicate the number of ionic bonds that can be formed, and not just the charge on the ions. 

Substantial latitude is available in determining what detail can be given in the nodes in order to extend the descriptive power of the representation for search purposes. Thus, one might further differentiate by giving the count of atoms in the nodes, or by detailing the molecular formula, and so on. 

Extending the concept of isomerism from molecules to ensembles of molecules (EM) leads to a mathematical model of cons itutional chemistry ). An EM is described by its list of the molecular species in the form of suitable chemical formulas. For an EM one can define two types of empirical elementary formulas, on one hand the ensemble formula, on the other hand a partitioned empirical ensemble formula which consists of the molecular formulas of the molecules in the EM. 

This critical compilation of pK values is a supplement to an earlier monograph by Kortum, Vogel, and Andrussow (see item [73]). This volume extends the literature coverage to the end of 1970 and summarizes data for some 4500 acids. In conjunction with the Kortum compilation, the total number of acids covered is si 5500. Each entry includes the name of the substance, its molecular formula, pK value the temperature, method of ateasure-ment, an assessment of reliability, and references to the literature. 

As we have seen in Chapters 23 and 24, isomers are different compounds that have the same molecular formula they have the same number and kinds of atoms arranged differently. The term isomers comes from the Greek word meaning same parts. Because their structures are different, isomers have different physical and chemical properties. Here we will extend our discussion of isomerism to include that caused by different arrangements of ligands about central metal ions. 

Fig. 1 Some early pointers to extended donor-acceptOT stacks, (a) Molecular formulas of four building blocks commonly used in the construction of D-A psendorotaxanes and MIMs. (b) The D-A stack formed between BIPY and DN38C10. (c) The D-A stack formed between a DNP unit with diethylene glycol appendages and CBPQ F. (d) The D-A stack formed by face-to-face packing of the [2]catenane comprising CBPQ P and DN38C10...

ACMF = augmented connectivity molecular formula AIC = atom invariant class CCAP = canonical code generation by automorphism permutation CSR ture representation EC = extented graph invariant atom partitioning ordered extended connectivity ITS structure. 

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