Tetramer and Pentamer

The diastereomers of the tetramer and the pentamer are difficult to identify using only the splitting pattern of the methylene protons. Several methylene proton resonances overlap around 1.8 ppm, and the methylene protons adjacent to the m dyad (eg. the rm proton in the rm isomer of the trimer) display an AB type splitting pattern in the dimer and the trimer. Therefore, the isomers of the tetramer and the pentamer were identified by using the following information concerning the dimer and trimer  

The intensity of each signal of the spectrum measured at 150 C was determined for polystyrenes prepared with benzoyl peroxide, n-butyllithium, and trifluoroboron etherate catalysts. The observed relative intensities of the signals were in good agreement with the calculated values assuming Bernoullian statistics with Pr of 0.54, 0.56, and 0.45 for the radical, anionic, and cationic polystyrenes, respectively (Table II). The value of the radical polystyrene was nearly the same as that reported by Shepherd et al. (10). 

Source Ref. 13. Used with permission of John Wiley Sons, Inc. Copyright 1983. 

Signal Chemical Shift (ppm) Assignment BPO obsd. (Pr=0.54) Intensity (%) BuLi obsd. (Pr=0.56) obsdf Et 0 (Pr=0.45) 

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The ratio of cycHc to linear oligomers, as well as the chain length of the linear sdoxanes, is controlled by the conditions of hydrolysis, such as the ratio of chlorosilane to water, temperature, contact time, and solvents (60,61). Commercially, hydrolysis of dim ethyl dichi oro sil a n e is performed by either batch or a continuous process (62). In the typical industrial operation, the dimethyl dichi orosilane is mixed with 22% a2eotropic aqueous hydrochloric acid in a continuous reactor. The mixture of hydrolysate and 32% concentrated acid is separated in a decanter. After separation, the anhydrous hydrogen chloride is converted to methyl chloride, which is then reused in the direct process. The hydrolysate is washed for removal of residual acid, neutralized, dried, and filtered (63). The typical yield of cycHc oligomers is between 35 and 50%. The mixture of cycHc oligomers consists mainly of tetramer and pentamer. Only a small amount of cycHc trimer is formed. 

The product is a mixmre of dimers, trimers, tetramers, and pentamers having an average RON (Research Octane Number) = 95. Table 3-14 shows the analysis of feed and products from dimerization of propylene. ... 

Among the recently published works, the one which showed that the cyclic structures of water clusters open up to form a linear structure above a certain threshold electric field value a was a systematic ab initio study on the effect of electric field on structure, energetics, and transition states of trimer, tetramer, and pentamer water clusters (both cyclic and acyclic) [36], Considering c/.v-butadiene as a model system, the strength and the direction of a static electric field has been used to examine the delocalization energy, the probabilities of some local electronic structures, the behavior of electron pairs, and the electronic fluctuations [37]. Another recent work performed by Rai et al. focused on the studies using the DFT and its time-dependent counterpart of effects of uniform static electric field on aromatic and aliphatic hydrocarbons [38],... 

Many iso-enzymes are hybrids of a limited number of sub-units. Some enzymes show multiple forms owing to increasing levels of polymerization of a single sub-unit these should not really be called iso-enzymes, because they do not have any genetic difference between the different forms. Cholinesterase, for instance, shows five forms consisting of a single sub-unit existing as monomers, dimers, trimers, tetramers and pentamers. 

The major components are series of homologous trimers, tetramers, and pentamers of the three acids 44-46, along with smaller quantities of dimers, hexamers, and heptamers. Furthermore, the secretion contains several isomers of each oligomer, furnishing a combinatorial library of several hundred macro-cyclic polyamines [51, 52]. Using repeated preparative HPLC fractionation, the most abundant trimeric, tetrameric and pentameric earliest-eluting compounds were isolated. One and two-dimensional H NMR spectroscopic analyses showed that these molecules were the symmetric macrocyclic lactones 48, 49, and 50 (m, n, o, p, q=7) derived from three, four or five units, respectively, of acid 46. Moreover, using preparative HPLC and NMR methods, various amide isomers, such as 53,54, and 55 (Fig. 9) were also isolated and characterized [51,52]. 

Liquid Chromatography-Electrospray Ionization Mass Spectrometric Characteristics ([M - H] and Product Ions) of Selected Proanthocyanidin Tetramers and Pentamers from Pinto Beans, Plums, and Cinnamon, Respectively... 

The existence of the alcohol shows that the butyl lsopropenyl ketone formed was again attacked by BuLi. The field desorption mass spectra of the trimer, tetramer and pentamer showed only their own ", (M+1)+ and (M+2)+ peaks, and the mass numbers of M " peaks... 

More recently Okawara, Hotta and Shimura (48) hydrolyzed the more reactive dichlorodiethoxysilane in a benzene-pyridine mixture, isolated the corresponding linear dimer, tetramer, and pentamer, and obtained evidence for the presence of smaller amounts of the cyclic dimer, trimer and tetramer. The partial hydrolysis of tetramethoxy-, tetra-ethoxy-, tetra-n-butoxy- and tetra-iso-pentoxysilane in alcohol-water mixtures was studied by Takatani (83) and the following products isolated ... 

Extraction of thorium and europium by these same compounds shows an increase from 051 to Os5 (Table 4.26). Thorium is equally extracted by the linear tetramer and pentamer, whereas europium is even better extracted by linear tetramer than by the linear pentamer. Most of the CMPO calixarenes extract europium better than TOPO and OOCMPO. All these extractants are stronger extractants of thorium than europium, because similar efficiencies require ligand concentrations of 10-3 M for... 

Commercial polymerization was once used only for converting the olefins from cracked gases into motor fuel. However, it is rapidly becoming very important in the production of such petrochemicals as heptene, propylene dimer, trimer, tetramer and pentamer and the alkylated aromatics such as ethylbenzene, isopropylbenzene, cymene, and butyl-benzenes. This list may be expected to grow as new uses are found for the heavier olefins. 

Crans, D.C., C.D. Rithner, and L.A. Theisen. 1990. Application of time-resolved 51-V 2-D NMR for quantitation of kinetic exchange pathways between vanadate monomer, dimer, tetramer, and pentamer. J. Am. Chem. Soc. 112 2901-2908. 

Table II and Figure 1 data show di-2-ethylhexyl azelate (DEHZ) has excellent low viscosity at low temperature along with good volatility properties. Figure 1 shows the DEHZ to have substantially lower volatility than DIOA and actually lower volatility than 4 cSt polyalphaolefin (PAO-4) in the initial distilled loss area of the curves. The slopes of the PAO and petroleum curves in Figure 1 indicate they are composed of a distribution of different molecular weight species, whereas the relatively flat curves of the esters indicate they are essentially composed of a single chemical species. As a result, there are little or no low molecular weight ends to increase the volatility of these diesters. Even though the PAO is a very narrow distillation cut, it is still composed of a blend of dimers, trimers, tetramers, and pentamers, and does exhibit volatility caused by the low ends as demonstrated in Figure 1.

Figure 16.8 Influence of an increasing gradient of gum arabic concentration on the interactions between BSA (5 x 104mM) and a fraction of procyanidins from grape seed (gallate tetramers and pentamers, 0.034gl" ) (in 12% aqueous ethanol, 0.1 M acetate buffer, pH 5.0) [81].

Figure 16.10 Influence of the concentration of procyanidins (gallate tetramers and pentamers) on the aggregation with two salivary proteins (a) a-amylase (0.4pM) and (b) IB8c (0.5p/W) in 12% aqueous ethanol, 3.1 mM acetate buffer, pH 5.0 [104],...

Oligomerization of butene over HMordenite has been carried out at 5 MPa and 523 K. The reaction gave mainly dimers and trimers with a minor fraction of tetramers and pentamers.[13] In contrast, oligomerization of butene over solid phosphoric acid catalyst gave mainly dimers. 

Figure 9 shows a comparison of the infrared absorption and VCD spectra of (L-Ala), n = 3 - 5. The spectra are normalized for equal absorption intensity at 1595 cm 1, which is the frequency of the carboxylate anion antisymmetric stretching mode. The data show that the amide I intensity increases roughly linearly with the number of peptide linkages in the molecule, and that the VCD intensity increases similarly. However, the positions of the infrared absorption maxima are shifted from about 1654 cm 1 in the trimer to 1648 cm 1 in the pentamer. Similarly, the VCD zero crossing in the trimer occurs at 10 cm 1 higher frequency than in the tetramer and pentamer. We have interpreted these results [48] in terms of different solution conformations of the peptides the trimer seems to be stabilized by zwitterionic interactions, as discussed before, whereas formation of extended helices seems to occur at the level of the tetramer. 

The reaction of the tetrafluoroethylene tetramer and pentamer with ethylacetoacetate gives pyran derivatives 107 and 108, respectively (83JCS(P1)1239, 83JCS(P1)1235). 

The cholates 8.117-8.119 were designed for the preparation of dynamic hbraries with different binding affinities for alkah metal ions. The presence of a polyether chain in position 7 of 8.117 provided a recognition element for metal binding that was absent from the disubstituted p-methoxybenzyl substitution pattern of 8.118, while the 7-deoxy derivative 8.119 was even less prone to metal coordination. The three monomers were submitted to transesterification/cyclization protocols, either without metal templates or using different alkali metal salts as templates. The relative abundances of cyclic dimers, trimers, tetramers, and pentamers for each experiment are reported in Table 8.7. 

Procyanidin dimer, trimer, tetramer, and pentamers have molecular masses of 578, 866, 1154, and 1442, respectively. They can be easily identified using a mass spectrometer if [M H] m/z 577, 865, 1155, or 1441 are observed. Proanthocyanidins have three fragmentation... 

There is some evidence for a small amount of cooperativity in the HCCH trimer, albeit of a lesser degree due to the absence of a true H-bond. The interaction energy of the cyclic trimer is very nearly equal to three times that of a single dimer, even though each pairwise geometrical relationship is distorted from the true T-shape favored by the dimer. The tetramer and pentamer are also likely to be of cyclic type, but again little variance is observed in the H-bond energy per pairwise interaction. 

In the late 1960s, as part of an effort devoted to the preparation of high-order annulene polyoxides, J. A. Elix attempted a Wittig-type self-condensation of 5-formyl-2-furfurylphosphonium chloride 1.19 While the products that resulted were predominantly polymeric, small quantities of macrocyclic products were isolated. These latter consisted of trimers, tetramers, and pentamers (discussed in Chapters 2, 4, and 6, respectively), as well as a hexamer. Unfortunately, this hex-americ [36]annulene hexoxide product represented by structure 7.80, was only obtained in 0.05% yield (Scheme 7.7.1). Thus, Elix was unable to elucidate the exact configurational arrangement of the double bonds in this product. Still, as discussed below, this issue could be addressed at least in part, by spectroscopic means. 

Moreover, it is convenient to employ multipolar multicenter expansions of e.g. electrostatic and polarization terms, that are expressed as functions of properties of the separate interacting systems. In any case, it is wise to validate models built this way by comparison with results of supermolecular calculations. For instance, the ASP-Wn potentials yield non-additivity estimates in agreement with that obtained in the supermolecular approach for a number of configurations of trimers, tetramers and pentamers of water [109]. 

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