Cyclic compounds structural formulae

FIGURE 20.1 Acyclic fiagments (Fig. 20.1a) and their combinations (Fig. 20.1b) characteristic for highly medium and low effective antitumor compounds (structural formulas of the cyclic fragments are given in Table 20.5). 

Structurally unique, potent, and selective oxytocin antagonistic agents characterized by a cyclic hexapeptide structure have recently been isolated from the broth filtrate of a novel Streptomyces silvensis strain [434,435]. As shown in formula (106), these compounds contain two hexahydro-3-pyrid-azinecarboxylic acid moieties. A study has been made of their structural modifications (including oxidation of the reduced pyridazine nuclei) [436]. 

For compounds containing only double-bonded atoms, the reference plane contains the double-bonded atoms and is perpendicular to the plane containing these atoms and those directly attached to them. It is customary to draw the formulas so that the reference plane is perpendicular to that of the paper. For cyclic compounds the reference plane is that in which the ring skeleton lies or to which it approximates. Cyclic structures are commonly drawn with the ring atoms in the plane of the paper. 

Complete fundamental cyclic formulas showing all carbons and hydrocarbons are given only in Charts 1, 2, 4, 8, and 9 in the other charts, the conventional ter-pene skeletal formulas have been used. For those not familiar with these common terpene formulas of the monocyclic and bicyclic structures, Chart 2 is included to show the different forms of identical structures which appear in current chemical literature. Only saturated structures are given. The three-dimensional type of skeletal formulas shown for the bicyclic structures is being used currently more and more because they often permit much more to be expressed concerning the properties of a compound and its relations to a fundamental type than do the classical structural formulas. 

The structural formulas of several cyclic compounds containing both nitrogen and sulfur are shown in Figure 17.4. Basic to the structures of these compounds is the simple ring structure of thiazole. It is a colorless liquid (bp, 117°C). One of its major uses has been for the manufacture of sulfathiazole, one of the oldest of the sulfonamide class of antibacterial drugs. The use of sulfathiazole is now confined to the practice of veterinary medicine because of its serious side effects. 

Alkenes are said to be unsaturated because they are capable of adding hydrogen in the presence of a catalyst. The product, an alkane, is called saturated because it cannot react with any more hydrogen. The presence of a pi bond of an alkene (or an alkyne) or the ring of a cyclic compound decreases the number of hydrogen atoms in a molecular formula. These structural features are called elements of unsaturation. Each element of unsaturation corresponds to two fewer hydrogen atoms than in the saturated formula. 

It has been supposed that the angle of least strain of the rings or polyhedra is 135°, which is most closely realised in the tetra-compound, which is also the most stable of the series. The structure assigned will determine that of the corresponding metaphosphimic acid which is produced by hydrolysis. Dimetaphosphimic acid, if its existence is admitted, could not be cyclic according to formula (a). Formula (b) is adopted in describing these compounds. 

A-cyclic or Open Chain Compounds.—Such compounds, because their structure is that of a chain of carbon groups, the ends of which chain do not unite to form a ring, are known as open chain or a-cyclic compounds in distinction from closed chain or cyclic compounds which we shall meet with in the second part of our study. Their structure explains also the general formula for the series as given at the top of the table, viz., CnH2n+2- Each carbon atom excepting the two end... 

Symmetry of Benzene.—If then benzene is acarbo-cyclic compound, as is so strongly indicated by its relationship to cyclo-hexane, the structural formula should express first of all this equivalence or likeness of the hydrogen atoms. In any geometric representation of such a condition we would naturally indicate it by a symmetrical figure. 

The question of whether the phosphonitrilic chlorides have cyclic or linear structures has been frequently discussed in the literature. The structural evidence will be considered in Section lY, where it will be seen that the cyclic formulation is established beyond doubt for the trimer and tetramer, and is highly probable for the higher soluble polymers it will meanwhile be assumed for all compounds of formula (PNX2) . For reasons considered in Section II, C the petrol-insoluble fraction (PNCUln PCls is believed to consist of a mixture of linear polymers. The two series are related, in that the linear compounds of low molecular weight are intermediates in the formation of the cyclics by the ammonolysis of phosphorus pentachloride. 

Tri-, tetra- to polycyclic compounds (part B) appear in the structural formula index in order of ring size (carbocyclic before heterocyclic ring compounds) under appropriate compound headings. Part C contains spiro compounds with similar ordering followed by part D which contains assemblies of identical cyclic systems (c.g., bicyclopropyl). 

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