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Stereoisomers of cyclic compounds

Draw the stereoisomers of the following amino acids. Indicate pairs of enantiomers and pairs of diastereomers. [Pg.167]

Because the compound has two asymmetric centers, it has four stereoisomers. Enantiomers can be drawn for both the cis isomer and for the trans isomer. Each of the four stereoisomers is chiral. [Pg.167]

Which of the following compounds has one or more asymmetric centers  [Pg.168]

Draw all possible stereoisomers for each of the following a. 2-chloro-3-hexanol c. 2,3-dichloropentane [Pg.168]

Of all the possible cyclooctanes that have one chloro substituent and one methyl substituent, [Pg.168]


The presence of two or more substituents on a ring—any size ring—introduces the possibility of stereoisomers. The existence of stereoisomers is independent of conformations and should be analyzed first because different stereoisomers will have different conformations. It is easiest to examine the stereoisomers of cyclic compounds by considering the rings to be flat, even though they may actually exist in chair or other conformations. Once all the stereoisomers have been identified, the conformations of each can be scrutinized. [Pg.205]

The cis- and trans-stereoisomers of cyclic compounds that were presented previously are actually just special cases of the type of stereoisomers that we have just discussed. For example, consider the case of 1,2-dimethylcyclohexane ... [Pg.234]

As we found when we considered acyclic compounds containing two stereogenic centers, the number of stereoisomers of cyclic compounds depends on whether or not the centers are equivalent. This also true for cychc compounds. First, we U examine the isomeric cis- and 1-bromo-2-chlorocyclobutanes (Figure 8.14a). These compounds are diastereomers. The compounds in Figure 8.14 are arranged to demonstrate the mirror image relationship of the two tram enantiomers, whose configurations are IR,2R and 15,25. There are also two enantiomeric cis isomers. [Pg.261]

In Summary The presence of more than one stereocenter in a molecule gives rise to diastereomers. These are stereoisomers that are not related to each other as object and mirror image. Whereas enantiomers have opposite configurations at every respective stereocenter, two diastereomers do not. A molecule with n stereocenters may exist in as many as 2" stereoisomers. In cyclic compounds, cis and trans isomers are diastereomers. [Pg.188]

Diastereomers are stereoisomers that are not related to each other as object to mirror image. Cis and trans isomers of cyclic compounds are examples of diastereomers. [Pg.204]

In open-chain compounds, the molecule can usually adopt that conformation in which H and X are anti periplanar. However, in cyclic systems this is not always the case. There are nine stereoisomers of 1,2,3,4,5,6-hexachlorocy-clohexane seven meso forms and a dl pair (see p. 161). Four of the meso compounds and the dl pair (all that were then known) were subjected to elimination of HCl. Only one of these (1) has no Cl trans to an H. Of the other isomers, the fastest elimination rate was about three times as fast as the... [Pg.1301]

Although the allylation reaction is formally analogous to the addition of allylic boranes to carbonyl derivatives, it does not normally occur through a cyclic TS. This is because, in contrast to the boranes, the silicon in allylic silanes has little Lewis acid character and does not coordinate at the carbonyl oxygen. The stereochemistry of addition of allylic silanes to carbonyl compounds is consistent with an acyclic TS. The -stereoisomer of 2-butenyl(trimethyl)silane gives nearly exclusively the product in... [Pg.816]

Configurations in cyclic compounds are considered in the same way as for acyclic compounds. If you cannot get an answer with the first atom, move on to the next, even though this may mean working around the ring system. Consider, for example, the stereoisomer of 3-methylcyclohexanol. [Pg.82]

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. [Pg.87]

Figure 21. The equilibrium between the helical interlaced system precursor of the trefoil knot and its face-to-face analogous complex leading to the face-to-face complexes. Interconversion between the two isomeric cyclic products is, of course, not possible. For the cyclic compounds, the total number of atoms x connecting two phenolic oxygen atoms is 16 if n=4 (pentakis(ethyleneoxy) fragment) or 19 if n = 5 (hexakis(ethyleneoxy) linker). Each knot is represented by the letter k accompanied by the overall number of atoms included in the cycle. The face-to-face complexes contain two monocycles (letter m), the number of atoms in each ring also being indicated. It can be noted that each knot has a face-to-face counterpart. For instance [Cu2(k-90)]2+ and [Cu2(m-45)2]2+ are constitutional isomers. They are by no means topological stereoisomers [34, 35]. Figure 21. The equilibrium between the helical interlaced system precursor of the trefoil knot and its face-to-face analogous complex leading to the face-to-face complexes. Interconversion between the two isomeric cyclic products is, of course, not possible. For the cyclic compounds, the total number of atoms x connecting two phenolic oxygen atoms is 16 if n=4 (pentakis(ethyleneoxy) fragment) or 19 if n = 5 (hexakis(ethyleneoxy) linker). Each knot is represented by the letter k accompanied by the overall number of atoms included in the cycle. The face-to-face complexes contain two monocycles (letter m), the number of atoms in each ring also being indicated. It can be noted that each knot has a face-to-face counterpart. For instance [Cu2(k-90)]2+ and [Cu2(m-45)2]2+ are constitutional isomers. They are by no means topological stereoisomers [34, 35].
The four different groups attached to a chiral carbon can be different elements, isotopes, or functional groups, and chiral centers can be present in bodi open-chain molecules or cyclic compounds. The recognition of chirality and chiral centers in molecules is an important step in determining the numbers of stereoisomers that are possible for a given compound. [Pg.129]

To obtain further information on the acc and the interactkm of the tm> functional groups in the cyclic peptides, Kopjde etaL 163) compared the reactivities of stereoisomers. For this purpose, the compariscm was made between two epimos, Cyclo-(Gly-Tyr-Gly-Gly-His< ly) (1,4-cfs) and Cydo-(Gly-D-T5w-Gfy-Gfy-His-Gly) 1,4-tram) Cyclo-(Tyr-His) (1,2-cts) and Cyclo-(D-T) -His) (1,2-Oans). The symbols following the names of the compound represent the positions of the hhddyl and the tyro l residues by the numbers and the configurations of the two a mmetric carbons, by cis for L-L-type and tram for D-L-type. Accordir to this representation, Cyclo-(Gly-His-Gly-Tyr-Gly-Gly), described earlier, can be represented as l,3[Pg.70]

The Julia olefin synthesis is rather like the Wittig reaction with a sulfone instead of a phosphonium salt but with one other important difference the elimination step is stereoselective and both dia-stereoisomers of the intermediate can give the same isomer of the alkene. Treatment of the sulfone 147 with a strong base gives the anion 148 (or a metal derivative) that combines with an aldehyde to give a diastereomeric mixture of adducts 149. Elimination by various methods gives, in open chain compounds, mostly -150 but, in cyclic compounds, mostly the Z-alkene.29... [Pg.239]

Acetylation of 38 with acetic anhydride afforded only the N,0-diacetyl compound 63 which on hydrolysis gave compound 62, the optical antipode of 54. Although the formation of the two C-7 epimeric alcohols in the reaction of 59 with hydrochloric acid supports an attack on a hydroxyl anion of a C-7 carbonium ion— the formation of a single stereoisomer 63 by the action of acetic anhydride may be more satisfactorily explained if the reaction proceeds by way of cyclic intermediate 64 such as the acetyl cation and an acetoxy anion which are derived from the same molecule of acetic anhydride. [Pg.286]


See other pages where Stereoisomers of cyclic compounds is mentioned: [Pg.167]    [Pg.167]    [Pg.167]    [Pg.167]    [Pg.3700]    [Pg.261]    [Pg.227]    [Pg.84]    [Pg.161]    [Pg.462]    [Pg.494]    [Pg.57]    [Pg.57]    [Pg.546]    [Pg.328]    [Pg.131]    [Pg.54]    [Pg.708]    [Pg.314]    [Pg.106]    [Pg.3]    [Pg.187]    [Pg.36]    [Pg.1088]    [Pg.206]    [Pg.462]    [Pg.314]    [Pg.158]    [Pg.54]    [Pg.199]    [Pg.77]    [Pg.456]   
See also in sourсe #XX -- [ Pg.167 , Pg.168 ]




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Cyclic compounds

Stereoisomer

Stereoisomers

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