Relative configuration, definition

The appropriateness and essence of this distinction between absolute and relative configuration in this case may be illustrated by a hypothetical experiment. By definition, the determination of an absolute configuration involves a comparison with a fixed reference standard. Such a standard may be simulated by an enzyme that can discriminate between the isomers 16a and 16c, which differ in the configuration of the central atom. If the reacting isomer 16a is represented by (2/ ,3r,4S)-2,4-dihydroxy-3-((/ )-[2-2H]-propionoxy)glutaric acid, it can be predicted with confidence that the enzyme will also react with the enantiomer... 

Structures 1 and 1, with identical relative configuration at C-2. C-3, are not covered by Masamune s very scant directions which do not include a guideline on the definition of the backbone. Thus, an allylmetal expert , having prepared 1 as one member of a series with the substituent of the ally] group varied, will probably describe 1 as syn, but investigators working on aldol reactions or conjugate additions will certainly prefer the term anti for 1. ... 

The preparation of aldol adducts may occur with simple diastereoselectivity. A definition of the term was given in Section 11.1.3. In a slightly different formulation, simple diastereoselectivity means that a single relative configuration is established at two neighboring C atoms that become stereocenters for the following reasons (1) Both C atoms were sp2-hybridized in the reactants one was part of a nonhomotopic C=X double bond and the other was part of a nonhomotopic C=Y double bond. (2) The formation of a (7-bond between these C atoms causes them to be sp3-hybridized in the reaction product. 

Relative configuration A definition of the molecular co-ordinates relative to an arbitrary standard. 

The i"C chemical shift thus reveals the relative configuration of substituents in molecules with a definite conformation, e.g. the axial position of the OH group in trans-3-methylcyclohexanol, cis-4-methylcyclohexanol, -D-arabinofuranose and a-D-xylopy-ranose (Table 2.12). It turns out, in addition, that these compounds also take on the conformations shown in Table 2.12 (arabinopyranose, C the others, CJ if they occurred as the other conformers, then the OH groups on C-l in these molecules would be equatorial with the result that larger shifts for C-l, C-3 and C-5 would be recorded. A ring inversion (50 50 population of both conformers) would result in an average C shift. 

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. 

A simple conceptual illustration of the appheation of RDCs is in the differentiation of axial and equatorial protons in pyranose sugars 103 through the eonsideration of one-bond Dch values [125]. Within the moleeular fiamework, all axial protons share the same parallel orientation (bond veetors in blaek) and thus exhibit RDCs of the same size, whereas the equatorial protons point in different directions (vectors in red) and so display different values, enabling their identifieation. A similar analysis allows the definition of the relative configuration of a dihydropyridone 10.4 [126]. In the trans isomer, the highlighted C-H... 

The first relation, (a) => (b), follows directly from the formal definition of the pair correlation function. A qualitative argument is the following gap governs the average density of molecules of species a at a certain relative configuration with respect to a molecule of species If the field of force produced by a j molecule is the same as that produced by an a molecule, then the local density of molecules at any point is independent of the species of the molecule that produces the field of force. 

L. E. Overman, J. Am. Chem. Soc. 2005, 127, 15652-15658. Total synthesis of (-)-crambidine and definition of the relative configuration of its unique tetracyclic guanidinium core, (c) F. Cohen, L. E. Overman, /. Am. Chem. Soc. 2006, 128, 2594-2604. Evolution of a strategy for the synthesis of structurally complex batzeUadine alkaloids. Enantioselective total synthesis of the proposed structure of batzeUadine F and structural revision. 

Thus, the three types of triads with different relative configurational structure can be distinguished on the basis of m and r dyads. To be meaningful, such a representation requires that the last monomer unit of the preceding dyad be taken into consideration in the definition of the next dyad it is just a consequence of the covalent linking of the constituting units ... 

Overman LE, Rhee YH. Total synthesis of (—)-crambidine and definition of the relative configuration of its unique tetracyclic guanidinium core. J. Am. Chem. Soc. 2005 127(44) 15652-15658. 

While there are no problems in the definition of the configuration leading to 0, difficulties are encountered in the procedure to reproduce the electrochemical situation. In fact, Eq. (17) has meaning only if the M/S interface has exactly the same structure during the measurement of E (relative to a reference electrode-electrochemical configuration) as well as during the measurement of 0. ... 

The first part of this book is dedicated to a discussion of mass spectrometry (MS) instrumentation. We start with a list of basic definitions and explanations (Chapter 1). Chapter 2 is devoted to the mass spectrometer and its building blocks. In this chapter we describe in relative detail the most common ion sources, mass analyzers, and detectors. Some of the techniques are not extensively used today, but they are often cited in the MS literature, and are important contributions to the history of MS instrumentation. In Chapter 3 we describe both different fragmentation methods and several typical tandem MS analyzer configurations. Chapter 4 is somewhat of an outsider. Separation methods is certainly too vast a topic to do full justice in less than twenty pages. However, some separation methods are used in such close alliance with MS that the two techniques are always referred to as one combined analytical tool, for example, GC-MS and LC-MS. In effect, it is almost impossible to study the MS literature without coming across at least one separation method. Our main goal with Chapter 4 is, therefore, to facilitate an introduction to the MS literature for the reader by providing a short summary of the basic principles of some of the most common separation methods that have been used in conjunction with mass spectrometry. 

The extends relation serves two purposes. First, it is used to define certain user-visible behaviors as increments relative to an existing definition—for example, to define different interaction paths based on configurations or incremental releases of functionality. Second,... 

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