Anti nomenclature

The longest linear chain for the syn-anti nomenclature in this case is defined as the segment that contains both stereogenic centers. 

Syn/anti nomenclature is mainly employed for octahedral complexes when geometric isomerism arises from the presence of a fused ring. Therefore, the syn isomer has adjacent fused rings whereas the anti isomer has opposite fused rings [5]. 

For aldol products many types of nomenclature have been proposed. Throughout this chapter the syn/anti nomenclature of Masamune is adopted and defined as shown in (3) and (4). 

We will use the syn/anti nomenclature [5] to describe the relative configuration of aldol stereoisomers, and the Ik/ul nomenclature [6] to describe the topicity of the reaction. For definitions, see glossary. Section 1.6. 

Heathcock et al. described the process that formed diastereomers in the aldol condensation, from precursors that do not contain a chiral center, as simple diastereoselectivity.209,210 Naming protocols to describe the diastereomers produced in the aldol condensation include the erythro/threo nomenclature, as well as the syn/anti nomenclature was discussed in Section I.4.B. Using this latter convention, diastereomers 340 and 343 were designated as anti and diastereomers 341 and 342 were designated as syn. 

Protonation of the anion [SN2] by acetic acid in diethyl ether produces the thermally unstable sulfur diimide S(NH)2. Like all sulfur diimides, the parent compound S(NH)2 can exist as three isomers (Scheme 5.5). Ab initio molecular orbital calculations indicate that the (cis,cis) configuration is somewhat more stable than the (cis,trans) isomer, while the (trans,trans) isomer is expected to possess considerably higher energy. The alternative syn,anti or E,Z nomenclatures may also be used to describe these isomers. The structures of organic derivatives S(NR)2 (R = alkyl, aryl) are discussed in Section 10.4.2. 

Hantzsch s proposal is consistent with characteristic infrared vibration frequencies of syn- and a fr-diazoates, suitably labeled with 15N, measured by Kiibler and Liittke (1963) and by an X-ray structure determination of a sy -diazoate by Alcock et al. (1980b). It is appropriate, therefore, to replace the syn/anti by the (Z/E) nomenclature for isomers (Sec. 7.1)... 

We have now introduced into our nomenclature a distinction between structure and anti-structure defects. What this means is that stacking faults can sometimes result in the formation of and Mx defects. These... 

Twenty-two years later the isolation of the anti-pernicious anemia factor" was announced independently by Smith (5) and Riches (6). Seven years of chemical studies identified 5,6-dimethylbenzimidazole (7), D-ribose (5) and amino-propanol (9) as components of the anti-pemicious anemia factor", but the tetrapyrroline ring structure containing Co(III) awaited the X-ray crystallographic data on the cyano-derivative by Hodgkin and White (10—15). Once the structure of the antipemicious anemia factor was determined it was called Vitamin B12 (cyanocobal-amin). The recommendations of a number of commissions forms the basis of the present system of nomenclature for this molecule and these are presented in Fig. 1. 

Because the new language incorporated an anti-phlogiston outlook, the book had many detractors. Nevertheless, the nomenclature found rapid acceptance among chemists, who realized that it was far superior to the chaotic assemblage of names used before. Today, Lavoisier s and Guyton s system of nomenclature is still the international language of chemistry. 

More complex is the problem of syn and anti eliminations (cis and trans in the older nomenclature), i.e. whether the substituents on Ca and leave the parent compound from synperiplanar or from antiperiplanar positions, viz. 

The hypothesis was discussed by K. Auwers and V. Meyer, H. Goldschmidt, E. Muller, A. Hantzsch, E. Beckmann, etc. In order to distinguish between these isomeric forms of, say, the benzaldoxim.es, A. Hantzsch employs the term syn as a prefix to indicate that the hydroxyl group lies on the same side of the mol. as the hydrogen atom of the aldehyde, and anti when the hydrogen and hydroxyl lie on opposite sides of the mol. The same nomenclature is applied to other compounds, e.g. the potassium benzoylphenyldiazotates, etc. Thus ... 

The following nomenclature rules apply to describing the transition state structures. The terms exo/endo refer to orientation of the chain starting from the enophile and proceeding to the ene. Endo means that the chain points in the direction of the ene, whereas in an exo form it points away from the ene. E and Z describe the geometry of the double bond of the ene. Syn and anti characterize the positions of the vinylic hydrogen atoms relative to each other. 

The stereochemistry of the cycloadducts in intramolecular Diels-Alder reactions depends upon the different geometry of the possible transition states 37—40 whose nomenclature can be explained as follows The orientation with the chain connecting the diene and dienophile lying under or above the diene is called endo. The opposite means exo. E and Z mark the geometry of the diene double bond which is connected with the chain. Syn and anti describe the arrangement of the hydrogen atoms (or substituents) at the prestereogenic centers which are involved in the C-C bond formation.12... 

In another study, Fourcroy is cast as the historian of the chemical revolution, a role he fulfils admirably as he was both spectator and participant in the most important chemical events of the period.230 The importance of the language of chemistry has been stressed by Trevor Levere231 and by Pierre Laszlo.232 It has also been contended that the new chemistry contained the seeds of later structural concepts.233 This may be pushing the potential of Lavoisier s anti-phlogistic chemistry and its revised nomenclature too far, yet without all these main components, the fundamental reorganization of chemistry could not have been achieved. Fresh interest was also stimulated in Lavoisier s collaborators and contemporaries. For example, the... 

Addition reactions to unsymmetrical alkenes in which a reagent with the structure H—X transfers the H atom to the less-substituted C atom and the X group to the more substituted C atom give, according to an old nomenclature, a so-called Markovnikov addition product. On the other hand, addition reactions of reagents H—X in which the H atom is transferred to the more substituted C atom of an unsymmetrically substituted C=C double bond and the X group is transferred to the less substituted C atom lead to a so-called anti-Markovnikov addition product. 

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