The stereochemistry of carbon

TJhe structural formulae of carbon compounds were originally based on the four bond pictures  

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For a discussion of such rules, see Eliel The Stereochemistry of Carbon Compounds, McGraw-Hill New York. 1962, pp. 68-74. For reviews of the stereochemistry of addition to carbonyl compounds, see Bartlett Tetrahedron 1980, 36, 2-72, pp. 22-28 Ashby Laemmle Chem. Rev. 1975, 75, 521-546 Goller J. Chem. Educ. 1974, 51, 182-185 Toromanoff Top. Stereochem. 1967, 2, 157-198. 

The stereochemistry of conjugate additions requires similar considerations to those used to predict nucleophilic attack on a carbonyl. Acyclic substrates may yield up to three contiguous chiral centres (Scheme 18). The relative stereochemistry of carbons C(l) and C(2) will depend upon the approach of the two reagents. The stereochemistry of carbon C(3) will depend upon the lifetime of the intermediate 30 if it has even a short lifetime it will take up the most stable conformation. For example, the base-catalysed additions of ethanol-d and 2-methyl-2-propanethiol-d to ethyl crotonate give a (2R, 3R )/(2R, 3S ) diastereoisomeric ratio of the addition products of approximately 10 190. The authors90 suggest the reaction proceeds in two steps and the protonation of the enolate determines the stereoselectivity. 

Tetrahedron. A geometrical solid form bounded by four plane surfaces in the stereochemistry of carbon and silicon, the tetrahedral figure represented by the tetravalent central atom and the four valence bonds directed at an angle of 109° 28 to one another. 

For reviews, see Eliel, E.L. The Stereochemistry of Carbon Compounds, McGraw-Hill, NY, 1962, pp. 68-74. For reviews of the stereochemistry of addition to carbonyl compounds, see Bartlett, P.A. 

So far in our study of organic chemistry, we have devoted considerable time to the spatial arrangement of atoms and groups attached to carbon atoms, that is, to the stereochemistry of carbon. Now let us look briefly at the stereochemistry of nitrogen. 

The terminology and notation that have been used to describe coordination compounds have been derived with one notable exception from the terms and symbols developed to describe the stereochemistry of carbon compounds. The terms ois, trans endo, exo dextro, d, D, (+) and leva, l, L (-) all have been used to describe the stereochemistry of coordination compounds in a close analogy with organic compounds (see Figure 1). As the descriptions of the chemistry and structures of coordination systems have become more varied and complex, the meanings of these terms have become less precise, as in the example of a ois or trans tricarbonyl octahedral compound (see Figure 2). The terms fao and mer were coined to indicate the facial and meridional disposition of substituted octahedral structures. 

Fig. 12-3 Bile acid and bile salt detergents. (A) Cholic acid drawn showing the stereochemistry of carbon atoms in the system effused rings, (B) glycocholate, and (C) taurocholate.

The ring A modification was undertaken on the enone 97, obtained in two steps from 69 (Scheme 13). The first route studied, shown on the left of the scheme, suffered from poor yields in formation of the allylic alcohol 98. Therefore, an alternative sequence was investigated in which the stereochemistry of carbon-carbon bond formation at C-12a was controlled by the C-4b methyl group. 

NMR spectroscopy can be used to characterize these carbon skeletons, relatively large sample amounts (10-100 p,g) in nearly pure form are required. Frequently, natural product chemists are fmstrated by the unavailability of large samples. But, they can be characterized by GC/ FTIR. Svatos and Attygalle" have demonstrated that GC/ FTIR data allow definitive deductions to be made about the stereochemistry of carbon-carbon double bonds conjugated to a vinyl group. 

The first strong attack upon the concept of valence follows two pages later "the difference in valences is a somewhat obscure concept because valence itself is not a clear concept" (KT 49). (This is one of the passages quoted verbatim by Jorgensen (20y, see also (7).) The attack is prepared at a metaphorical level with many nouns, verbs, and adjectives belonging to the semantic field of the opposition obscure/clear, and is followed by a triumphant exclamation "Thus a stereochemistry of cobalt compounds and platinum compounds appears alongside the stereochemistry of carbon compounds and nitrogen compounds "(WB 300 KT 50). 

Let us demonstrate an application of formulae Eqs. (25) and (26) on the example of methane molecule with sp hybridization. The stereochemistry of carbon atom is characterized by four unit vectors corresponding... 

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