Non-statistical distribution

It is supposed that the main factor for a non-statistical distribution in the formation of complexes is the destruction of the initial specific conformation of the matrix125. Two possible cases have been considered126 ... 

H.-L. Schmidt (2003) Fundamentals and systematics of the non-statistical distribution of isotopes in natural compounds. Naturwissenschaften 90, 537-552... 

The stereochemical outcome of this oligoselective polymerization is of some interest. In principle, eight stereoisomeric macrocycles 94 can be formed. However, HPLC analysis of the cyclized material revealed that only six of these possibilities are represented in the product mixture. In benzene as solvent, over half of the product mixture is a single stereoisomer, whereas in methyl isobutyrate as solvent the diastereomers are more evenly distributed. Preliminaty attempts to ascertain the relative stereochemistry of the major isomer within 94 via DNOE NMR measurements did not allow unambiguous assignment. Without this structural information in hand, further speculation on the relationship between chain stereochemistry and cyclization efficiency within 99 (see Scheme 8-27) is not warranted. Nevertheless, there must be some influence, given the non-statistical distribution of isomers. In comparison, the H-NMR spectrum of the pMMA portion of uncontrolled oligomer 95 is superimposable with that of atactic (i.e., random stereochemistry) pMMA. 

Previous explanations of the impact modification effect and its phase transition like the brittle-to-tough transition have assumed a basically statistical distribution of the dispersed rubber phase in the continuous polymer matrix [139], From there the critical interparticle distance model originated [139b], which is essentially a percolation-type theoretical interpretation. Experimental results like those reported by Bucknall [139a], but also many crack surfaces published in the literature, show that more rubber phase is present in the visible area of the crack surface than would be expected from a statistical distribution, SEM evaluations are consistent with our findings of a non-statistical distribution, but a phase separation of the dispersed material into some kind of layer. 

Further mechanistic studies ruled out the original pairwise [2 + 2] mechanism and provided additional support for the Chauvin mechanism. Labeling studies, such as the experiment in Fig. 4.18, revealed that the kinetic product (the product at low conversion) of the metathesis of 1,7-octadiene derivatives is a statistical distribution (1 2 1) of d -, d2-, and ii 44abeled ethylene [58]. This is inconsistent with the pairwise [2 + 2] mechanism, which would have produced a non-statistical distribution (1 1.6 1) of labeled ethylene. 

Earlier work by Schrodt and Libby (1954) and MacKay and Libby (1957) reported non-statistical distribution of the hexanes. Radiochemical impurities in the hexanes were probably at fault here. 

On the other hand, the Hatch-Slack photosynthetic cycle is important for tropical grasses, com and sugarcane. Phosphenol-pyr-uvate carboxylase is responsible for the primary carboxylation reaction. The first stable carbon compound is a C-4 acid, which is subsequently decarboxylated (101,102). The fundamentals and sys-tematics of the non-statistical distributions of isotopes in natural compounds have been reviewed (103). 

Cellulose ethers with non-statistical distribution of functionai groups... 

They are similar and significantly differ from the emission due to the F + I2F reaction as shown in Fig. la. The population analysis for both systems resulted in more non-statistical distributions which are nearly identical within the error bars, as shown in Fig. 2b. If an interpretation in terms of the KaMer and Lee mechanism is again attempted here this leads to several contradictions. Firstly the different energetics of Ae two reaction systems should be reflected by the chemiluminescence spectra. Secondly, the threshold for the formation of QIF is significantly higher than for I2F (24.7 kJ mol compared with 17.6 U moT ) [2]. Thirdly, one would expect the formation of electronically excited FQ and FBr as anticipated by Kahler and Lee rather than excited IF [2]. Finally, the enthalpy for the reaction F + QIF with AHg = -182.1 kJ mol is far from sufficient to populate the B state of IF where at least 226.7 kJ mol is required. (Although the stability of BrIF is not exactly known, the argument also holds for tiie F + BrDF reaction). 

The solubility of the donor and acceptor. A good solvent provides a random distribution of donor and acceptor molecules, whereas a poor solvent might lead to a non-statistical distribution with clumping together of donor and/or acceptor molecules. The non-statistical distribution could lead to anomalously high or low energy transfer rates and efficiencies. 

Estimations of the network parameter by Flory-Rehner equation had formal nature in view of non-statistical distribution of crosslinks. ... 

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