Number of Possible Isomers

PilR74 Pilgrim, R. L. C. The number of possible isomers in the porphyrins. J. Chem. Education 51 (1974) 316-318. 

As the number of carbon atoms increases, the number of possible isomers becomes larger. Whereas there are only two isomeric butanes, there are three isomeric pentanes. With hve carbons, in addition to the open-chain compounds shown, a stable ring compound known as cyclopentane is also possible. Five- and six-membered carbon rings are very stable because the bonds between carbon atoms in these size rings are close to the 109° angle preferred by carbon. Three- and four-membered hydrocarbon rings are also known, but they are less stable because of the required distortion of the bond angle. 

Interestingly, since all constitutive units and linkages can be distributed at random within a polymer, the number of possible isomers increases expo-... 

Read the entire laboratory activity. Form a hypothesis about the shapes of hydrocarbons and how the increase in the number of carbon atoms in a compound will affect the number of possible isomers. Record your hypothesis on page 171. 

Drawing a Conclusion Describe the relationship between the number of carbon atoms in an alkane and the number of possible isomers. 

Similarly, three isomers of pentane, C5H12, exist. As the number of carbon atoms in a molecule increases, the number of possible isomers increases markedly. Theoretically, for the formula c2()h... 

The polymerization of monosubstituted vinyl compounds that give polymers like PS and PP produces polymer chains that possess chiral sites on every other carbon in the polymer backbone. Thus, the number of possible arrangements within a polymer chain is staggering since the number of possible isomers is 2" where n is the number of chiral sites. For a relatively short chain containing 50 propylene units the number of isomers is about 1 x lO. While the presence of such sites in smaller molecules can be the cause of optical activity, these polymers are not optically active since the combined interactions with light are negated by other similar, but not identical, sites contained on that particular and other polymer chains. Further, it is quite possible that no two polymer chains produced during a polymerization will be exactly identical because of chiral differences. 

Phenols are a major chemical lump present in coal liquids. Phenols have basically one or more aromatic ring structures with alkyl substituents. Methyl, ethyl and propyl are the most common alkyl substituents. The smallest specie is the one with a hydroxyl group attached to a benzene ring. Addition of a methyl group produces three isomers - o-, m-, and p-cresols. It appears that all three are present in more or less same proportion. The number of possible isomers increases as the possible number and size of alkyl substituents increases. It is expected that higher... 

This second branched molecule is called isobutane. Compounds sharing the same molecular formula but having different structures are called structural isomers. Normal butane and isobutane have different physical properties. The number of structural isomers for the alkanes is included in Table 15.1. It can be seen in this table that as the number of carbon atoms increases that the number of possible isomers also increases. The fact that numerous isomers exist for most organic compounds is another reason why there are so many organic compounds. 

The number of possible isomers belonging to this division is very great for, in addition to those of which the normal acids... 

The number of acids possessing the same atomic weight, and belonging to this division, is determined, first, by the comple mentary variation of the two alcohol radios, and, secondly, by the number of possible isomers of these radicals. The two lowest terms of the series are alone incapable of isomeric modification by either of the causes mentioned. 

Stereoisomerism in compounds with two stereo centres diastereomers and meso structure In compounds whose stereoisomerism is due to tetrahedral stereocentres, the total number of stereoisomers will not exceed 2", where n is the number of tetrahedral stereocentres. For example, in 2,3,4-trihydroxybutanal, there are two chiral carbons. The chiral centres are at C-2 and C-3. Therefore, the maximum number of possible isomers will be 2 = 4. All four stereoisomers of 2,3,4-trihydroxybutanal (A-D) are optically active, and among them there are two enantiomeric pairs, A and B, and C and D, as shown in the structures below. 

The electrochemistry of C86, C90, and C92 has been reported for isomeric mixtures of individual cages.8 As the cage size of the fullerene increases, the yield of fullerenes decreases significantly. In addition to this, the number of possible isomers also increases, which in turn makes separation of isomers difficult. Thus, no reports appear in the literature indicating the electrochemical behavior of a single isomer of empty... 

A second form of isomerism occurs with mixed metal polyanions, such as [PW8V404o]7, in which the relative positions of the W and V atoms may vary.56 That such positional isomers do exist has been amply demonstrated by NMR and ESR spectroscopy.57 The numbers of possible isomers increase with the lowering of skeletal symmetry, e.g. five for ar-[PWioV204o]5-, fourteen for /3-[SiMo2Wi0O4ol4. ... 

In fact, as will be shown later, direct substitution of bromine for hydrogen with compounds such as this does not occur readily, and when it does occur, the four possible substitution products indeed are formed, but in far from equal amounts because there are differences in reactivity for substitution at the different positions. Actually, some of the substitution products are formed only in very small quantities. Fortunately, this does not destroy the validity of the substitution method but does make it more difficult to apply. If direct substitution fails, some (or all) of the possible substitution products may have to be produced by indirect means. Nonetheless, you must understand that the success of the substitution method depends on determination of the total number of possible isomers —it does not depend on how the isomers are prepared. 

Octaarylbipyrroles. The photochemical dissociation of the dimer of tetraphenylpyrrole to give the pink radical (XIIIA XIIIB) was reported by Blinder et al. (66). The exact nature of the dimer XIIIA is in question since there are a large number of possible isomers. A discussion of the analysis of the EPR spectrum of XIIIB is included in Sec. IV. The absorption spectrum of the radical, generated by ultra-... 

The synthesized fullerene hydrides vary both in the composition and in the isomeric structures. The number of possible isomers of the C60H2n fullerene hydrides varies over a wide range from 23 for C60H2 to >1015 for C60H30 (Balasubramanian 1991). In the synthesis, the mixtures are formed with a limited number of isomers due to thermodynamic and kinetic limitations. However, the synthesis of fullerene hydrides of high purity is still impossible due to the above mentioned peculiarities. The best samples correspond to the isomeric mixtures containing 1-5% of the hydrides of different formula. 

Theoretical calculations have shown that C60H36 and consequently also its deuterated analogous are molecules with a number of possible isomers (Balasubramanian 2004). Symmetry considerations (Balasubramanian 2004) and thermodynamic calculations (Karpushenkava et al. 2007) restrict the number of stable isomers. Vibrational spectroscopic analysis combined with theoretical calculations have shown that the most stable isomers are those with symmetry S6, T, Th, D3d (Meletov et al. 2001 Karpushenkava et al. 2007 Bini et al. 1998). The predominant... 

They have the same molecular mass, but differ in their manner of linkage, their branching, and in the order (sequence) of their atoms (constitutional isomers). The number of possible isomers increases rapidly in higher generations - by analogy with the classical case of the alkanes. 

Constraints (a) and (b) decrease the number of possible isomers for C5H5M(CO)2L2L3 derivatives to only three, namely, two enantiomeric isomers having L2 and L3 cis to each other, and one achiral isomer having L2 and L3 trans to each other, shown in the first line of Scheme 8. Because of constraint (c), the achiral trans isomer is excluded, and the two isomers shown in Scheme 8 (second line), are left as the only possible isomers. Thus, by introducing three constraints, the stereochemistry of a square pyramid can provide a pair of mirror-image isomers (51, 73). 

The challenge is to derive intramolecular connectivity from chemical composition. Once this has been achieved all further molecular properties can, in principle, be deduced. However, the first step is clearly impossible As the number of atoms per molecule increases, so does the number of possible isomers, and there are no criteria for ranking the isomers. The only way to predict connectivity is from a historical record, such as a synthetic pathway, which, in turn, depends upon reaction conditions and the nature of primary reactants. 

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