Isomers, designating

The use of D and L is gradually being replaced by the R and S system of designating isomers, which is particularly useful when more than one chiral carbon atom is present. 

Although the product isomers are shown as resulting via a dissociation process, the products are equally valid for associative mechanistic considerations, as indicated by Figure 2. Attachment of G anywhere on the top half of [M ABCDEF] prior to the release of A will result in isomer G. (The designation isomer G is based on the ligand atom which is trans to atom F in the octahedron and is the atom at the top of the octahedron as drawn. The other isomers can be similarly differentiated.) Isomer G... 

The designations isomer-a and isomer-b are those of the reviewer, and are used for convenience of exposition. 

Werner introduced some other practices such as the use of /z to signify a bridging group, of -ol for bridging hydroxyl groups, and of cis and trans or numbers to designate isomers. 

The preparation of aryl pyrazole anthranilic diamides with designated Isomer A regiochemistry is outlined in Figure 3. Esters 8 imderwent base hydrolysis to the acids 10 that were converted to the acid chlorides with oxalyl chloride and coupled with anthranilic amides 11 to afford the anthranilic diamide products of formula 12 in moderate yield. 

The pair of isomers designated as and trans 2 butene have the same constitution both have an unbranched carbon chain with a double bond connecting C 2 and C 3 They differ from each other however m that the cis isomer has both of its methyl groups on the same side of the double bond but the methyl groups m the trans isomer are on oppo site sides of the double bond Recall from Section 3 11 that isomers that have the same constitution but differ m the arrangement of their atoms m space are classified as stereoisomers as 2 Butene and trans 2 butene are stereoisomers and the terms as and trans specify the configuration of the double bond... 

Isomers are distinguished by lettering the peripheral sides of the parent beginning with a for the side 1,2, and so on, lettering every side around the periphery. If necessary for clarity, the numbers of the attached position (1,2, for example) of the substituent ring are also denoted. The prefixes are cited in alphabetical order. The numbers and letters are enclosed in square brackets and placed immediately after the designation of the attached component. Examples are... 

When two different substituents are attached to each carbon atom of the double bond, cis-trans isomers can exist. In the case of c T-2-butene (Fig. 1.11a), both methyl groups are on the same side of the double bond. The other isomer has the methyl groups on opposite sides and is designated as rran5--2-butene (Fig. l.llb). Their physical properties are quite different. Geometric isomerism can also exist in ring systems examples were cited in the previous discussion on conformational isomers. 

The HCFC-225 isomers designed to replace CFC-113 are manufactured by Lewis acid promoted addition of HCFC-21 to tetrafluoroethylene... 

The two carbons that bear no numbers are common to both rings and carry no hydrogen atoms. From the symmetrical configuration of the naphthalene molecule, it should be possible for only two isomers to exist when one hydrogen atom is replaced by another atom or group. Therefore, positions 1, 4, 5, and 8 are identical and often are designated as "a" positions likewise, positions 2, 3, 6, and 7 are identical and are designated as "P" positions, as shown in (2). 

DiisononylPhthalate andDiisodeeylPhthalate. These primary plasticizers are produced by esterification of 0x0 alcohols of carbon chain length nine and ten. The 0x0 alcohols are produced through the carbonylation of alkenes (olefins). The carbonylation process (eq. 3) adds a carbon unit to an alkene chain by reaction with carbon monoxide and hydrogen with heat, pressure, and catalyst. In this way a Cg alkene is carbonylated to yield a alcohol a alkene is carbonylated to produce a C q alcohol. Due to the distribution of the C=C double bond ia the alkene and the varyiag effectiveness of certain catalysts, the position of the added carbon atom can vary and an isomer distribution is generally created ia such a reaction the nature of this distribution depends on the reaction conditions. Consequendy these alcohols are termed iso-alcohols and the subsequent phthalates iso-phthalates, an unfortunate designation ia view of possible confusion with esters of isophthaUc acid. 

The asterisk signifies an asymmetric carbon. AH of the amino acids, except glycine, have two optically active isomers designated D- or L-. Isoleucine and threonine also have centers of asymmetry at their P-carbon atoms (1,10). Protein amino acids are of the L-a-form (1,10) as illustrated in Table 1. 

When ofloxacin was first introduced it was made available as the racemate. Later the optical isomers were prepared and it was found that the (3)-enantiomer, DR 3355 (6b), was substantially more active (8—128-fold) than the (R)-isomer against a broad range of bacteria (47—50). This chiral preference is not unique to ofloxacin and has been demonstrated in other quinolones as well (51,52). This significant finding has already had an impact on the design of new quinolone antibacterials still in development (53). 

The 6-methoxymethylene penicillanic acid [93040-42-7] (31, R = CH OCH (2)-isomer, R" = R " = 3) designed to mimic the amino acrylate species found usiag clavulanic acid and sulbactam. Upon the reaction of this compound with the enzyme, the potential exists for further Michael addition to inactivate the enzyme. The compound is indeed a -lactamase inhibitor but no synergy data have been reported. The related imine stmcture... 

Scheme 4 also represents the classical route to isoxazoles, first studied in 1888 by Claisen and his coworkers (1888CB1149). Reaction of a 1,3-diketone with hydroxylamine gives, via the isolable monoxime (108) and the 4-hydroxyisoxazole (109), the isoxazole (110). Unsym-metrical 1,3-diketones result in both possible isomers (110) and (111), but the ratio of the isomeric products can be controlled by the right combination of the 1,3-dicarbonyl component and the reaction conditions used. These important considerations are described in Chapter 4.16, along with the variations possible in the 1,3-dicarbonyl component designed to yield diverse substituents in the resultant isoxazole. 

Diastereomers include all stereoisomers that are not related as an object and its mirror image. Consider the four structures in Fig. 2.3. These structures represent fee four stereoisomers of 2,3,4-trihydroxybutanal. The configurations of C-2 and C-3 are indicated. Each stereogenic center is designated J or 5 by application of the sequence rule. Each of the four structures is stereoisomeric wife respect to any of fee others. The 2R R and 25,35 isomers are enantiomeric, as are fee 2R, iS and 25,3J pair. The 21 ,35 isomer is diastereomeric wife fee 25,35 and 2R,3R isomers because they are stereoisomers but not enantiomers. Any given structure can have only one enantiomer. All other stereoisomers of feat molecule are diastereomeric. The relative configuration of diastereomeric molecules is fiequently specified using fee terms syn and anti. The molecules are represented as extended chains. Diastereomers wife substituents on the same side of the extended chain are syn stereoisomers, whereas those wife substituents on opposite sides are anti stereoisomers. 

Chemical Designations - Synonyms Amyl Acetate, Mixed Isomers Pentyl Acetates Chemical Formula CHjCOOCjHn. 

Chemical Designations - Synonyms Isodecaldehde, mixed isomers Trimethylheptanals Chemical Formula C,Hi,CHO. 

It is often the case that chemists involved or familiar with ethylene oxide (oxiran) chemistry refer to these cyclic oligomers as EO-4, EO-6 and EO-7 respectively. Such designations are informal if not colloquial but, like any name, are useful if they correctly convey an idea. The difficulty with these informalities, indeed with the crown nomenclature system is that it cannot adequately deal with complicated structures or even isomers of simple ones. 

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