Stereoisomers configurational

However, in a cyclohexane system we also need to consider the conformational mobility that generates two different chair forms of the ring (see Section 3.3.2). Let us consider 3-methylcyclohexanecarboxylic acid. This has two chiral centres, and thus there are four configurational stereoisomers. These are the enantiomeric forms of the trans and cis isomers. 

The same stereochemical principles are going to apply to both acyclic and cyclic compounds. With simple cyclic compounds that have little or no conformational mobility, it is easier to follow what is going on. Consider a disubstituted cyclopropane system. As in the acyclic examples, there are four different configurational stereoisomers possible, comprising two pairs of enantiomers. No conformational mobility is possible here. 

For the 2 last units of the living chain each possessing 2 asymmetrical carbons, we can propose 4 configurational stereoisomers ... 

Obviously, among the 4 configurational stereoisomers, none seems strongly favored. Thus, from the structure of the living species only, we cannot propose a stereoregulating mechanism and we searched for an explanation by the mode of complexatlon of monomer molecules to the active centers. 

According to Ernest L. Eliel and Samuel H. Wilen in Stereochemistry of Organic Compounds (1994, p. 102), configurational stereoisomers result from arrangments of atoms in space of a molecule with a defined constitution without regard to arrangements that differ only by rotation about one or... 

The cyclohexene substructure resulting from Diels-Alder addition of acyclic dienes to fullerenes can adopt two boat conformations.50,387-389 If a new stereogenic center is generated during the cycloaddition, the boat-to-boat interconversion leads to conformational diastereoisomerism in each configurational stereoisomer.389,390 Such a case was studied by Zhang and Foote who performed VT (variable temperature) XH NMR and NOE measurements on... 

Stereoisomers have the same molecular formula, but their atoms have a different spatial arrangement — a different configuration. Stereoisomers are classified as -Enantiomers when the isomers are mirror images of each other and cannot be superimposed... 

From a legal point of view it is interesting to note that up to now (IR)-configured stereoisomers of 3-oxo-p-methane-8-thiol have not been detected in nature. Therefore, those stereoisomers have to be classified as artificial flavourings in the sense of order regulations by the European Union. 

Unusual Steric Course of Solvolysis of C9-Activated Alkaloids Access to C9-epi-Configured Stereoisomers... 

Different representations of the configurational stereoisomers of glyceraldehyde and of alanine. 

In the literature, both the (R,S) and the (S,S) diastereomers of lithium alkyl 2 have been proposed as the major diastereomer [4a, 5a]. Based on these predictions, both retention and inversion of the configuration at C(3) have been postulated for the reactions of (/ ,S)-2 with alkyl halides. Our X-ray structural analysis of (R,S)-2 shows that the reaction of the (/ ,iS)-configured stereoisomer and inversion of configuration [for the reaction of R,S)-2 with iodomethane in toluene] do in fact take place. 

Therefore, although the two structures represent enantiomers, they cannot be separated because they rapidly interconvert even at low temperature. They simply represent different conformations of the same compound. Therefore, structures (c) and (d) are not configurational stereoisomers they are conformational stereoisomers (see Section 4.9A). 

These stereoisomers are not readily interconverted by rotation around the double bond at room temperature. Like cis-trans isomers of cycloalkanes, they are configurational stereoisomers and can be separated from one another by distillation, taking advantage of the difference in their boiling points. 

The CH3CHXCHXCH3 molecule can exist as the stereoisomers shown here. In the echpsed conformation (meso) shown on the left (E), the molecule has a plane of symmetry that bisects the C2, C3 bond. This is a more energetic conformation than any of the three staggered conformations, but it is the only conformation of this configurational stereoisomer that has... 

Solution 13 The three configurational stereoisomers of 1,2-dimethylcyclopentane are shown here. Both trans stereoisomers are chiral, while the cis configuration is an achiral meso compoimd. 

A model of F is identical with its mirror image. It is achiral, although it does not have a plane of symmetry, due to the presence of a center of symmetry that is located between C2 and C3. A center of symmetry, like a plane of symmetry, is a reflection symmetry element. A center of symmetry involves reflection through a point a plane of symmetry requires reflection about a plane. A model of the mirror image of S (structure T) is not identical to S, but is a conformational enantiomer of S. They can be made identical 1 rotation about the C2, C3 bond. Since S and T are conformational enantiomers, the two will be present in equal amounts in a solution of this configurational stereoisomer. Both conformation S and conformation T are chiral and therefore should rotate the plane of plane polarized light. 

To avoid confusion between conformational and configurational stereoisomers we will call the former "conformers."... 

Many books erroneously drop the term "configurational and call configurational stereoisomers simply "stereoisomers for short. WATCH OUT The term stereoisomer is often used in place of configurational stereoisomer. ... 

Naming can be a great way to figure out the relationship between two molecules. For example If two molecules have the same name, they are the same or conformers. If two names differ only in the prefixes Z vs. E, the molecules are configurational stereoisomers. 

Name this molecule, draw and name its configurational stereoisomer, and construct an... 

Draw the configurational stereoisomer of the molecule you drew above. (If it has no configurational stereoisomer, your original structure is not correct.)... 

Make up an example (not appearing in this ChemActivity) of a pair of molecules that are a) eonstitutional isomers, b) conformers, c) configurational stereoisomers. 

In a subsequent activity we will break down the term configurational stereoisomers into finer categories, so it is critical that you are comfortable with the distinction between conformers, constitutional isomers, and configurational stereoisomers before you move on. 

Like Newman projections, Z/E configurational stereoisomers drive a few students toward the exit door each semester. And like Newman projections, a few minutes with a model always brings them back. If you are having trouble recognizing Z and E, make some models. 

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