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Conformations Stereoisomers

There are two major types of stereoisomer conformational isomers and configurational isomers. Configurational isomers include optical isomers, geometrical isomers, enantiomers and diastereomers. [Pg.37]

The staggered and eclipsed forms of ethane are conformational stereoisomers (conformational isomers, conformers) because they have the same molecular formulas and sequences of bonded elements but different spatial arrangements due to rotations around single bonds. (Actually there are an infinite number of conformational isomers (also called conformations) because there are an infinite number of degrees of rotation around the bond, but normally one only needs to be concerned with energy minima and maxima.)... [Pg.158]

Conditions, physiological s. Physiological conditions Configuration (s. a. Stereoisomers, Conformation)... [Pg.309]

There are some instances in which Etot is useful. If we are comparing stereoisomers, values of Etot provide useful relative energies. That is because stereoisomers will always have identical contributors to Etot, both in terms of the equations and the parameters involved. Since all structures along a torsional path are stereoisomers (conformers), Etot can be used to determine rotation barriers. Note that E,ot cannot be used for constitutional isomers, such as n-butane vs. isobutane. That is because different parameters are likely involved, such as a CH3-CHR2 k and r in isobutane vs. the CH3-CH2R k and r for w-butane. Only after E, t values for these two structures are converted to heats of formation can energy comparisons be made. [Pg.133]

Another reminder is to watch out for the term stereoisomer used by itself In many places and in many textbooks this term is used in place of the term configurational stereoisomer. (Recall that configurational stereoisomers are the E/Z, cis/trans, R/S, D/L, +/- enantiomers, diastereomers, etc. that we have been working with in this ChemActivity.) The strictly correct use of the term stereoisomer includes all stereoisomers. That is, both configurational stereoisomers and conformational stereoisomers (conformers—covered in ChemActivity 6A). [Pg.173]

There are two types of stereoisomers conformational and configurational isomers, and these are roughly divided into two classes enantiomers (optical isomers) and diastereomers (nonoptical isomers) see Figure 1.1. [Pg.5]

If compounds have the same topology (constitution) but different topography (geometry), they are called stereoisomers. The configuration expresses the different positions of atoms around stereocenters, stereoaxes, and stereoplanes in 3D space, e.g., chiral structures (enantiomers, diastereomers, atropisomers, helicenes, etc.), or cisftrans (Z/E) configuration. If it is possible to interconvert stereoisomers by a rotation around a C-C single bond, they are called conformers. [Pg.75]

Disubstituted cyclopropanes exemplify one of the simplest cases involving stabil ity differences between stereoisomers A three membered ring has no conformational mobility so the ring cannot therefore reduce the van der Waals strain between cis sub stituents on adjacent carbons without introducing other strain The situation is different m disubstituted derivatives of cyclohexane... [Pg.125]

Their heats of combustion (Table 3 2) reveal that trans 1 4 dimethylcyclohexane is 7 kJ/mol (17 kcal/mol) more stable than the cis stereoisomer It is unrealistic to believe that van der Waals strain between cis substituents is responsible because the methyl groups are too far away from each other To understand why trans 1 4 dimethylcyclo hexane is more stable than cis 1 4 dimethylcyclohexane we need to examine each stereoisomer m its most stable conformation... [Pg.126]

Orientation of methyl groups m most stable conformation Heat of combustion heat of combustion More stable stereoisomer... [Pg.126]

Determine whether the two structures in each of the following pairs represent constitutional isomers different conformations of the same compound or stereoisomers that cannot be inter converted by rotation about single bonds... [Pg.138]

The following are representations of two forms of glucose The six membered ring is known to exist in a chair conformation in each form Draw clear representations of the most stable con formation of each Are they two different conformations of the same molecule or are they stereoisomers Which substituents (if any) occupy axial sites ... [Pg.140]

Although both stereoisomers yield 4 tert butylcyclohexene as the only alkene they do so at quite different rates The cis isomer reacts over 500 times faster than the trans The difference in reaction rate results from different degrees of rr bond develop ment in the E2 transition state Since rr overlap of p orbitals requires their axes to be parallel rr bond formation is best achieved when the four atoms of the H—C—C—X unit he in the same plane at the transition state The two conformations that permit this are termed syn coplanar and anti coplanar... [Pg.216]

In Problem 4 25 you were asked to draw the preferred conformation of menthol on the basis of the information that menthol is the most stable stereoisomer of 2 isopropyl 5 methylcyclo hexanol We can now completely descnbe (—) menthol structurally by noting that it has the R con figuration at the hydroxyl substituted carbon... [Pg.323]

The aldotetroses are the four stereoisomers of 2 3 4 trihydroxybutanal Fischer pro jections are constructed by orienting the molecule m an eclipsed conformation with the aldehyde group at the top The four carbon atoms define the mam chain of the Fischer projection and are arranged vertically Horizontal bonds are directed outward vertical bonds back... [Pg.1029]

Molecular mechanics strain energies have another use They can also be used to com pare the energies of models that share the same molecular formula that is models that are either stereoisomers or different conformations of a single molecule (allowed com parisons are shown here)... [Pg.1263]

Stereoisomers of peroxides (4) and (5) are known to exist and their conformations have been studied using photoelectron, nmr, and other spectroscopic methods, and their crystalline stmctures have been deterrnined (122,154,155). [Pg.116]

With the development of accurate computational methods for generating 3D conformations of chemical structures, QSAR approaches that employ 3D descriptors have been developed to address the problems of 2D QSAR techniques, e.g., their inability to distinguish stereoisomers. The examples of 3D QSAR include molecular shape analysis (MSA) [34], distance geometry [35,36], and Voronoi techniques [37]. [Pg.359]

In addition to constitution and configuration, there is a third important level of structure, that of conformation. Conformations are discrete molecular arrangements that differ in spatial arrangement as a result of facile rotations about single bonds. Usually, conformers are in thermal equilibrium and cannot be separated. The subject of conformational interconversion will be discussed in detail in Chapter 3. A special case of stereoisomerism arises when rotation about single bonds is sufficiently restricted by steric or other factors that- the different conformations can be separated. The term atropisomer is applied to stereoisomers that result fk m restricted bond rotation. ... [Pg.76]

FIGURE 7.10 Stereoisomeric 2,3-butanediols shown in their eclipsed conformations for convenience. Stereoisomers (a) and (b) are enantiomers of each other. Structure (c) is a diastereo-mer of (a) and (b), and is achiral. It is called meso-2,3-butanediol. [Pg.303]


See other pages where Conformations Stereoisomers is mentioned: [Pg.689]    [Pg.355]    [Pg.97]    [Pg.43]    [Pg.689]    [Pg.355]    [Pg.97]    [Pg.43]    [Pg.489]    [Pg.60]    [Pg.127]    [Pg.131]    [Pg.183]    [Pg.183]    [Pg.217]    [Pg.421]    [Pg.827]    [Pg.39]    [Pg.442]    [Pg.32]    [Pg.181]    [Pg.677]    [Pg.127]    [Pg.183]    [Pg.183]    [Pg.421]    [Pg.827]   
See also in sourсe #XX -- [ Pg.43 , Pg.44 ]




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Conformational stereoisomer

Conformational stereoisomer

Conformational stereoisomers

Conformational stereoisomers

Conformations Stereoisomers around single bonds

Conformations Stereoisomers chair

Conformations Stereoisomers eclipsed

Conformations Stereoisomers staggered

Conformers isomers Stereoisomers

Stereoisomer

Stereoisomers

Stereoisomers conformers

Stereoisomers conformers

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