Molecular-type homologous series

The HcReynolds abroach, which was based on earlier theoretical considerations proposed by Rohrschneider, is formulated on the assumption that intermolecular forces are additive and their Individual contributions to retention can be evaluated from differences between the retention index values for a series of test solutes measured on the liquid phase to be characterized and squalane at a fixed temperature of 120 C. The test solutes. Table 2.12, were selected to express dominant Intermolecular interactions. HcReynolds suggested that ten solutes were needed for this purpose. This included the original five test solutes proposed by Rohrschneider or higher molecular weight homologs of those test solutes to improve the accuracy of the retention index measurements. The number of test solutes required to adequately characterize the solvent properties of a stationary phase has remained controversial but in conventional practice the first five solutes in Table 2.12, identified by symbols x through s have been the most widely used [6). It was further assumed that for each type of intermolecular interaction, the interaction energy is proportional to a value a, b, c, d, or e, etc., characteristic of each test solute and proportional to its susceptibility for a particular interaction, and to a value x, X, Z, U, s, etc., characteristic of the capacity of the liquid phase... 

The viscosity of a liquid is related directly to the type and size of the molecules which make up the liquid. The variation of liquid viscosity with molecular structure is not known with exactness however, the viscosities of liquids which are members of a homologous series are known to vary in a regular manner, as do most other physical properties. For example, pure paraffin hydrocarbons exhibit a regular increase in viscosity as the size and complexity of the hydrocarbon molecules increase. 

The molecular weight and the Kovats retention index can then be combined to aid in the identification of the component. A linear relationship exists between the molecular weight and retention index for a homologous series of compounds. The relationship varies for each class of compound thus, a clue can be obtained regarding the type of compound present which can be verified by some other technique. 

Reactions of limited proportions of amine and phosphine Lewis bases with non-molecular copper and silver halides generate crystalline cubanes. Crystallographic determinations of molecular structure have been reported for at least 31 complexes with cf or d10 metal configurations, spanning the following types or homologous series of compounds. Compilations of data occur in references 157, 158 and 167. 

In Figure 3, a straight-line relationship between a retention index and molecular weight is illustrated for homologous series of n-alcohols, n-aldehydes, n-acetates, and n-hydrocarbons. The compound having molecular weight 130 and retention index 1180 corresponds to n-pentyl acetate. Since the relationship in Figure 3 holds for all types of related compounds, it is obvious that this technique could be widely used in identification of GC peaks. 

Methods to Estimate p Solely from Molecular Structure Methods of this type are available with the GCM approaches. All methods presented in Section 7.3 allow temperature-dependent estimation of pv in the region specified. For certain homologous series, specific vapor pressure-structure-temperature relationships exist. For example, Woodman et al. [27] have reported the following relationship for a, w-dinitriles (3 < Nqh1 < 8) ... 

The molecular complexity of molybdenum (IV) alkoxides is determined by the size and ramification of the alkyl group — the polymeric (R = Me), dimeric (CN = 5, two bridging OR-groups, R = Pr ) with a double metal-metal bond, and even monomers (R = Bu ). The first representatives of W(OR)4 homologous series are tetramers with the [Ti4(OMe)16]-type structure. The derivatives of ramified or bulky alcohols are known only as mixed-ligand complexes (such as dimeric solvates of alkoxide halids with alcohols, various alkoxide hidrides and monomeric complexes with phenantroline, see Table 12.19). 

One of the most common types of ligand in supra molecular photochemistry is the bidentate chelate 2,2 bipyridine (bpy, 11.1), which represents the first member of the homologous series of polypyridyls that includes 2,2 6, 2"-terpyridine (tpy, 11.3) and carries on up to the helicate-forming sexipyridine... 

When two compounds in any homologous series have the same molecular formula but a different arrangement of atoms or groups of atoms, there is a possibility of a further type of isomerism called positional or structural isomerism. The bigger the molecule, the greater the possibilities of isomerism. Some theoretically possible isomers might not actually exist, due to their impossibly contorted shapes. 

Although aniline does possess a dipole moment the cohesion energy is predominantly of the London type. The critical solubility point—technically actually the i i demixing point—with hydrocarbon mixtures (aniline point) is an important characteristic quantity. The aniline point rises with the molecular weight in a homologous series. For aromatic hydrocarbons the critical solubility point is the lowest, for paraffins the highest, olefins and cyclic hydrocarbons are in between, in agreement with the variation of the specific cohesion (Table 33). 

In summary the results observed in these studies [160] of poly(Sty-co-DVB) swelling in aromatic liquids serve to show that the method of measuring a is so sensitive that it can detect an effect caused by even the smallest modification in the molecular geometry of attached substituents, and that these differences correlate qualitatively with expectation based on the known principles of physico-organic chemistry of aromatic compounds. Since the observed a is the net effect of electronic attraction and steric hindrance between the sorbed molecule and the adsorption site, i.e. the monomer unit of the polymer, it would be impossible to separate quantitatively the electronic and steric contributions of a particular substituent. The ability to make such a differentiation, however, appears to be more promising with liquids that comprise homologous series of the type Z(CH2)nH (where Z is a phenyl, chloro, bromo or iodo substituent), since the added electronic contribution to Z by each additional methylene group is well known to be extremely small when n becomes >3 [165],... 

Oils and asphaltenes, which constitute a partial characterization of coal liquids according to solvent extraction, are generally considered to be key intermediates in coal liquefaction. In this regard, the present results do reveal that the asphaltenes contain higher molecular weight homologs in many specific-Z series and different compound types than do the oils. However, our study unequivocally demonstrates that compound types are observed in both the oils and asphaltenes that are equivalent in molecular formula and, hence, presumably in molecular structure. Furthermore, the overlap in the compositions of the two fractions is quantitatively appreciable. Thus, isolation of oils and asphaltenes must involve, in addition to solubility, other physical/... 

The photolysis of a homologous series of methylene aziridines (aliphatic alleni-mines) has been shown to proceed via two major types of molecular elimination... 

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