Stereoisomers kinds

So, the triple density representation will not provide extra information on binary systems of stereoisomer kind. Such a situation is due to the fact that at any similarity level, the comparison of two densities becomes irrelevant and can be associated to a unique representation, which from a TDQSM point of view is represented by the triple selfsimilarity integral 0. This situation coherently follows from the fact that, upon origin shift, the two DF can be brought into a unique function only. 

Merrifield method See solid phase peptide synthesis Meso stereoisomer (Section 7 11) An achiral molecule that has chirality centers The most common kind of meso com pound IS a molecule with two chirality centers and a plane of symmetry... 

Rather similar was the paper [PolG36a] which also derives asymptotic formulae for the number of several kinds of chemical compounds, for example the alcohols and benzene and naphthalene derivatives. Unlike the paper previously mentioned, this one gives proofs of the recursion formulae from which the asymptotic results are derived. A third paper on this topic [PolG36] covers the same sort of ground but ranges more broadly over the chemical compounds. Derivatives of anthracene, pyrene, phenanthrene, and thiophene are considered as well as primary, secondary, and tertiary alcohols, esters, and ketones. In this paper Polya addresses the question of enumerating stereoisomers -- a topic to which we shall return later. 

A cycloalkane is a saturated cyclic hydrocarbon with the general formula C H2 . In contrast to open-chain alkanes, where nearly free rotation occurs around C, -C bonds, rotation is greatly reduced in cycloalkanes. Disubstituted cycloalkanes can therefore exist as cis-trans isomers. The cis isomer has both substituents on the same face of the ring the trans isomer has substituents on opposite faces. Cis-trans isomers are just one kind of stereoisomers—isomers... 

Molecules that are not identical to their mirror images are kinds of stereoisomers called enantiomers (Greek encmtio, meaning "opposite"). Enantiomers are related to each other as a right hand is related to a left hand and result whenever a tetrahedral carbon is bonded to four different substituents (one need not be H). For example, lactic acid (2-hydroxypropanoic acid) exists as a pair of enantiomers because there are four different groups (—H, -OH, - CH3, -C02H) bonded to the central carbon atom. The enantiomers are called (-i-)-lactic acid and (-)-lactic acid. Both are found in sour milk, but only the (+) enantiomer occurs in muscle tissue. 

R Stereoisomers (Section 4.2) are compounds whose atoms are connected in the same order but with a different geometry. Among the kinds of stereoisomers we ve seen are enantiomers, diastereomers, and cis-trans isomers (both in alkenes and in cycloalkanes). Actually, cis-trans isomers are just another kind of diastereomers because they are non-mirror-image stereoisomers. 

Diels-Alder reaction and. 494-495 El reaction and, 392 E2 reaction and, 387-388 R.S configuration and, 297-300 S 1 reaction and, 374-375 S -2 reactions and, 363-364 Stereogenic center, 292 Stereoisomers, 111 kinds of, 310-311 number of, 302 properties of, 306 Stereospecilic, 228, 494 Stereospecific numbering, sn-glycerol 3-phosphate and, 1132 Steric hindrance, Sjvj2 reaction and, 365-366 Steric strain, 96... 

Although they are built from the same numbers and kinds of atoms, structural isomers have different chemical formulas, because the formulas show how the atoms are grouped in or outside the coordination sphere. Stereoisomers, on the other hand, have the same formulas, because their atoms have the same partners in the coordination spheres only the spatial arrangement of the ligands differs. There are two types of stereoisomerism, geometrical and optical. 

The lUPAC 1974 Recommendations, Section E, Fundamental Stereochemistry, give definitions for most of the terms used in this chapter, as well as rules for naming the various kinds of stereoisomers. They can be found in Pure Appl. Chem., 1976, 45,... 

Syntheses follow a kind of bio-mimetic approach [283, 284] in building up the chain during a sequence of Wittig-type reactions or Horner-Wadsworth-Emmons olefination, adding two carbons to the chain at a time with either methyl- or ethyl-branches. As the final products need to be highly pure (E)-stereoisomers, reaction steps and purification need to be carefully controlled. 

These reactions can also be made enantioselective (in which case only one of the four isomers predominates) by using539 chiral enol derivatives,540 chiral aldehydes or ketones,541 or both.542 Since both new chiral centers are formed enantioselectively, this kind of process is called double asymmetric synthesis.543 A single one of the four stereoisomers has also been produced where both the enolate derivative and substrate were achiral, by carrying out the reaction in the presence of an optically active boron compound544 or a diamine coordinated with a tin compound.545... 

OPTICAL ISOMER- Either of two kinds of optically active three-dimensional isomers (stereoisomers). One kind is represented by mirror-image presence of one or more asymmetric carbon atoms in the compound (glyceraldehyde, lactic acid, sugars, tartaric add, amino acids). The other kind is exemplified by diastereoisomers, which are not mirror images. These occur in compounds having two or more asymmetric carbon atoms thus, such compounds have 2 optical isomers, where n is the number of asymmetric carbon atoms. 

Draw an atomic-orbital picture of 1,3-dichloropropadiene, CICH=C=CHCI. Examine the structure carefully and predict how many stereoisomers are possible for this structure. What kind of stereoisomers are these ... 

Optical isomers are special kinds of stereoisomers they are non-superimposable mirror images of each other (Fig. 16.27). Both geometrical and optical isomerism can occur in an octahedral complex, as in [CoCI2(en)2]+ the trans isomer is green (14a) and the two alternative cis isomers (14b) and (14c), which are optical isomers of one another, are violet. 

Isomers that have the same connections among atoms but a different arrangement of the atoms in space are called stereoisomers. In coordination chemistry, there are two kinds of stereoisomers diastereoisomers and enantiomers (we ll discuss the latter in Section 20.9). 

Obviously, all tris-chelates whose stereochemistry is analyzable in terms of the above model are stereochemically correspondent similarly, compounds of the type ArsZ, such as triarylboranes and triarylcarbenium ions are also stereochemically correspondent. However, the more interesting correspondence is that between the class of tris-chelates and the class of AraZ molecules. Although these two classes of molecules differ enormously in their chemical properties and reactions, the concept of stereochemical correspondence tells us that their stereochemical attributes are necessarily closely related. For example, a tris-chelate and a stereochemically correspondent triarylborane will each have the same number and kinds of stereoisomers, interconvertible by the same number and kinds of rearrangement pathways. 

Generally, four kinds of diastereomeric salts are derived from a combination of racemic acid [( )-A] and racemic base [( )-B] as shown below. Surprisingly, it has been found that one pair of less-soluble salts is spontaneously resolved from the four salts and four stereoisomers are resolved simultaneously by preferential crystallization. 

Stereoisomers have the same order of atom attachments but different arrangements of the atoms in space. Cis-trans isomerism is one kind of stereoisomerism. For example, two substituents on a cycloalkane can be on either the same (c/s) or opposite (trans) sides of the mean ring plane. Stereoisomers can be divided into two groups, conformational isomers (interconvertible by bond rotation) and configurational isomers (not interconvertible by bond rotation). Cis-trans isomers belong to the latter class. 

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