Position isomerism

Complications arising from other types of isomerism. Positional and geometrical isomerism, also described in Sec. 1.6, will be excluded for simplicity. In actual polymers these are not always so easily ignored. Polymerization of 1,2-disubstituted ethylenes. Since these introduce two different asymmetric carbons into the polymer backbone (second substituent Y), they have the potential to display ditacticity. Our attention to these is limited to the illustration of some terminology which is derived from carbohydrate nomenclature (structures [IX]-[XII]) ... 

The hydrogen-deuterium exchange rates for 1,2-dimethylpyrazolium cation (protons 3 and 5 exchange faster than proton 4 Section 4.04.2.1.7(iii)) have been examined theoretically within the framework of the CNDO/2 approximation (73T3469). The final conclusion is that the relative reactivities of isomeric positions in the pyrazolium series are determined essentially by inductive and hybridization effects. 

Cyclic enamines with an isomeric position of the double bond have been obtained by the addition of Grignard reagents to five- (78-81), six- (82-86), seven- (87-90), and thirteen- (89-91) membered lactams, whereas other medium-sized (92,93) lactams furnished amino ketones. The reaction has been extended to substituted lactams (94-98), and iminoethers (99,100). 

The formation of enamines from carbonyl compounds and secondary amines usually entails as only questionable structural feature, the possible isomeric position of double bonds in the product. Molecular rearrangements have not presented synthetic limitations. A notable exception is the generation of o-aminophenols on distillation of enamines derived from 2-acylfurans 620,621). 

Orts-funktion, /. position ftmction. -isomerie, /. place isomerism, position isomerism, Ortsteln, m, Min.) bog iron ore hardpan, ortsverinderlich, a. movable, portable, Orts-verinderung,/. change of position, -wech-sel, m. change of position or location, -zahl, /. position number, index number. 

The HLB numbers decrease with increasing chain length, e.g., from 13.25 for sodium decane 1-sulfonate to 9.45 for the C18 homolog [72]. Typical HLB numbers for positional isomers range from 12.3 for sodium dodecane 1-sulfonate to 13.2 for the more hydrophilic 6 isomer [73]. The HLB numbers of alkanesulfonates are less influenced by the isomeric position of the functional group and by substituents than the cM values [68]. HLB numbers can be correlated with partition coefficients for the distribution of a surfactant between the aqueous and oily phases, which emphasizes that the partition coefficient is dependent on the carbon number [68]. 

Substitution of two or more hydrogens in benzene results in positional isomerism. Positional isomers have the same formula, but different physical and chemical properties. In disubstituted benzene, three positional isomers are possible, as shown above. If the substituents are the same or different, one is always listed in the 1-position. If the substituents are different, they are listed alphabetically. 

The alkenes make up a homologous series of hydrocarbons with the general formula C H2 . Alkenes show two types of structural isomerism, position isomerism and chain isomerism. Geometrical isomerism also exists because of the lack of free rotation about the C=C double bond. 

Other factors of the molecular structure favour sorption, such as isomeric position for anionic, or the number of ethylene oxides in nonionic surfactants (see Table 5.4.5). There is an increased sorption in... 

As with the carbocyclic systems, the hydrogens on both N and C adopt axial and equatorial positions, and in the change from one conformer to the other the axial H inverts to the equatorial position and vice versa. There are many examples of ring systems in coordination chemistry which can adopt these conformational isomeric positions. Four systems currently being studied are the complexes of 1,2-propylenediamine, 1,2-f/ww-cyclo-hexanediamine, 1,2-fraw.y-cyclopentanediamine, and 2,3-butanediamine, and some reference will be made to each of these. 

When there are two or more substituents on a benzene ring, structural isomerization can result. For instance, there are three possible isomers of xylene (dimethylbenzene). The isomers are commonly designated as ortho, meta, and para. A letter (o, m, or p) designates the isomeric position. 

The rates of pyrolysis of o-, m- and z -methylphenylethyl chloride have been compared with that of ethyl chloride (Table 15). Even though the phenyl group participated in the HC1 elimination, electron release of the methyl group at the three isomeric position of the aromatic ring was found to be, within the experimental errors, ineffective on the rates when compared to the unsubstituted phenylethyl chloride. Consequently, the effect of the CH3 substituent was too small for the reinforcement of the phenyl assistance as reflected by the pyrolysis rate. 

Lunn and Senior35 proposed many years ago a mathematical model of isomerism in organic chemistry which Iliev generalized in recent years.36 38 Lunn and Senior considered three types of isomerism (i) univalent substitution isomerism (positional isomerism), (ii) skeletal (structural) isomerism and (iii) enantiomorphism. Univalent substitution isomerism is the relationship existing between any two compounds Ai and A2 with the same empirical formula in case that structural formula of A can be converted into that of A2 by a permutation of the univalent substituents without disturbing the skeleton. Then the molecules Ai and A2 are said to be univalent substitution isomers. For example, 1-chloropropane and 2-chloropropane are univalent substitution (positional) isomers. Skeletal isomers are any two compounds Ai and A2 with... 

Two compounds can have different structures because of a differing arrangement of the some groups in the positional isomerism (e.g. midine vs. pseudouridine). Compounds with the same molecular formula but with different functional groups are structural isomers (e.g. D-glucose vs. D-fructose) in structural isomerism. Positional isomers and structural isomers have different chemical and physical properties because of the different arrangement of the atoms. These two types of isomers (i.e. positional isomers and structural isomers), which differ in the manner in which atoms are connected or bonded together, are also called constitutional isomers. 

Chondroitin sulfate (ChSO.) is a polymer of glucuronic acid and glucosaminosulfate with two isomeric positions for the sulfate group (Fig. 1). We have mostly worked with the 4-isomer. 

Aoyama, T., Fukui, K., Tanagushi, K., Nagaoka, T., and Hashimoto, Y. (1996) Absorption and Metabolism of Lipids in Rats Depend on Fatty Acid Isomeric Position, J. Nutr. 126, 225-231. 

Fig. 1 Examples of one- and two-armed lariat ethers. The wavy line in structures 1 and 2 indicates that the sidearm may occupy isomeric positions.

Fig. 5.18. Partial RP-HPLC chromatogram of iodine isomerized positional CLA isomers from 6,8- to 13,15-18 2 as FAME. Chromatographic conditionsiTwo Vydac 201TP54 columns in series maintained at -5°C, elution under a MeCN/TFIF/hexane gradient, UV detection 233 nm.

Glyceryl trinitrate was converted by rabbits to the mono-and 1,3-dinitrate derivatives, which were excreted in the urine. The isomeric 1,2-glyceryl dinitrate was not detected as a metabolite of glyceryl trinitrate. After the administration of 1,2-glyceryl dinitrate, only glyceryl mononitrate (isomeric position unknown) was detected. The metabolism of penta-erythritol trinitrate (IV), an active metabolite of pentaerythritol tetra-nitrate, was studied in dogs. The major metabolites in the urine were pentaerythritol mononitrate and pentaerythritol only the latter compound was present in the feces. An oral dose of pentaerythritol was excreted unchanged by the dog. ... 

Two levels of comparison are used to describe the molecular structure. The first level excludes three-dimensionality and comprises substances having the same set of atoms but differing in how they are connected in the molecule. Constitutional (structural) isomers are isomers that diDer in the sequence in which atoms are connected to one another, so they can contain different functional groups and/or bonding patterns (e.g., branching). The constitution of molecules (number, kind, and connectivity of atoms) may be represented by a two-dimensional space. There are five types of constitutional (structural) isomerism chain isomerism, positional isomerism, functional isomerism, metamerism, and tautomeiism. 

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