Numbering system for

The stmcture of vitamin A [11103-57-4] and some of the important derivatives are shown in Figure 1. The parent stmcture is aH-Zra/ j -retinol [68-26-8] and its lUPAC name is (all-E)-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexen-l-yl)-2,4,6,8-nonatetraen-l-ol (1). The numbering system for vitamin A derivatives parallels the system used for the carotenoids. In older Hterature, vitamin A compounds are named as derivatives of trimethyl cyclohexene and the side chain is named as a substituent. For retinoic acid derivatives, the carboxyl group is denoted as C-1 and the trimethyl cyclohexane ring as a substituent on C-9. The stmctures of vitamin A and -carotene were elucidated by Karrer in 1930 and several derivatives of the vitamin were prepared by this group (5,6). In 1935, Wald isolated a substance found in the visual pigments of the eye and was able to show that this material was identical with Karrer s retinaldehyde [116-31-4] (5) (7). 

J. B. Casey, W. J. Evans, W. H. PoweU, and T. E. Sloan, "A Stmctural Definitive Descriptor and Numbering System for Cluster Compound Nomenclature," Chemical Abstract Service, presented at the 198th National Meeting of the American Chemical Society, Miami Beach, FI., Sept. 1989. 

Table 18. Basic Numbering System for Chromium-Bearing Low Alloy Steels...

Enified Numbering System for Metals and Alloys, SAE HE 1086 or ASTM DS-56A, 5th ed., 1989 Also available in electronic form on floppy disk. 

Unified Numbering System for Metals andMlloys, SAE HS 1086a or ASTM DS-56a, 2nd ed., 1977. 

This is not the normal numbering system for these molecules. 

Me. (CHj). CHMe. CHj. CHMe. (CH2)4Me and Schirm and Besendorf have synthesised the latter and identified it with the sparteine hydrocarbon. Clemo and Raper have modified Ing s formula to (VIII). The latter provides an explanation of the fact that sparteine yields two monomethiodides, which appear to be stereoiso-merides, but does not yield a dimethiodide. Examination of a space niodel of (VIII) shows that if the two octahydropyridocoline systems are both trans and if the C, — C, bridge is cis with respect to the hydrogen atoms attached to C and C the system is fairly rigid and the nitrogen atoms are so close to each other that the formation of a dimethiodide is Impossible. Couch has proposed a new numbering system for the Sparteine formula as shown in (Villa). 

The uses of an activation-numbering system for bicyclic compounds will be presented and the generalizations summarizing the reactivity... 

Figure 52.7 The SAE numbering systems for engine oils and gear oils are not related and must not be confused. This figure illustrates the differences...

Fluorinated compounds are frequently referred lo by code, such as F-l 15. To translate this code into a molecular formula, add 90 to 115. The firsl digit of the sum is the number of carbons the second, the number of hydrogens the third, the number ol fluorines chlorines complete the valences (i.e., C2F5CI is F-l 15 = 90 + 115 = 205. or C H Fj). A four-digit number is used for unsaturated molecules. See Tables 14.1-14.3 for the numbering system for chlorofluorocarbons. 

Many laboratories find it practical to keep separate records for these, which means that the sample numbering system for raw materials must be different from that used for finished products. Other laboratories lump everything together for the purpose of record keeping but have separate storage areas for the two types of samples. 

Many laboratories use a numbering system for their procedures for easy reference. Procedures should always be dated, since they will some day be superseded by new versions. At that time, the outdated ones should be carefully filed. There may be cases where reference will have to be made to them in the future. One person should be in chai ge of the methods books and make sure it is kept up to date. 

Fig. 16.6 The 1,3-diphenyl propane skeleton of flavonoids and the numbering system for flavonoids. Three structural features optimise the radical scavenging properties of a flavonoid (i) an orto-dihydroxy structure of the B-ring (catechol) (ii) 2,3 double bond in conjugation with a 4-oxo group (iii) 3- and 5-hydroxy groups (Bors and Saran, 1987).

Tetrazolium salts are derivatives of the H-tetrazole (1) or 2H-tetrazole (2). The CA numbering systems for tetrazoliums and formazans are shown in 3 and 4. It should be noted that the carbon atoms in 3 and 4 are... 

The sequence of operations involved in a PPP-MO calculation is illustrated in the flow diagram shown in Figure 2.13. The method is illustrated for the case of 4-aminoazobenzene, 15c. The first step involves devising a numbering system for all of the atoms that contribute to the 7r-system of the molecule. Secondly the total number of 7r-electrons in the... 

If an octahedral complex has the formula MX3Y3, there are two possible isomers. In an octahedron, the positions are assigned numbers so the locations of ligands in the structure can be identified. The usual numbering system for ligands in an octahedral complex is... 

Four deuteriated retinols, 26-29, with 3 to 5 deuterium atoms have been synthesized29 for metabolism of vitamin A studies in humans30. Deuterium has been introduced into appropriate intermediates, used in the reaction scheme shown in equation 12, by base-catalysed exchange with 2H20 or perdeuterioacetone. The numbering system for retinol (vitamin A alcohol) is shown in equation 12. 

Two commonly used numbering systems for the same molecule... 

Fig. 7.3. Molecular structure and suitable atomic numbering system for theophylline.

There are two generally accepted numbering systems for the bisindole-type alkaloids. The system used throughout the chapter is shown around formula 1 however, the biogenetic numbering system presented for vinblastine as formula lA is still in wide use. 

The currently accepted name for (1) in Chemical Abstracts is dibenzothiophene, although biphenylene, diphenylene, or biphenylylene sulfide are still used, especially in the Russian literature. Occasionally 9-thia-fluorene is used and recently, in one instance, dibenzo[6,d]thiophene. An alternative numbering system for (1) is met with on occasions in which C-4 is taken as C-1, as in carbazole. In the absenee of moleeular diagrams this system must be detected by reference to the chemistry described. For example, in a few dyestuff patents 2,7-diaminodibenzothiophene 5,5-dioxide is referred to and this is obviously the 3,7-diamino compound, also known as benzidine sulfone. 

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