Branching, effect

Butanes are chosen as the simplest models for the normal and branched isomers. Both branched and normal isomers contain a C-C bond (2 ) interacting with the terminal C-H bonds (2 and 2 ) (Scheme 26a). The cyclic -aj-a2 -a3 a2- interaction (Scheme 26b) occurs in the polarization of the middle C-C a-bond by the interactions with the antiperiplanar C-H a-bonds. The orbital phase is continuous in the branched isomer and discontinuous in the normal isomer (cf Scheme 4). The branched isomer is more stable. The basic rule of the branching effects on the stability of alkanes is ... 

We derived some rules of the branching effects on the stabilities. We used the cross conjugation numbers (nj. 

The ability of a dendritic shell to encapsulate a functional core moiety and to create a specific site-isolated microenvironment capable of affecting the molecular properties has been intensively explored in recent years [19]. A variety of experimental techniques have been employed to evidence the shielding of the core moiety and to ascertain the effect of the dendritic shell [19, 20]. Dendrimers with a fullerene core appear to be appealing candidates to evidence such effects resulting from the presence of the surrounding dendritic branches. Effectively, the lifetime of the first triplet excited state of fullerene derivatives... 

In the absence of any nonsize exclusion effects or branching effects, the concentration distribution within the chromatographic peak describes the polymer molecular weight distribution. The concentration distribution is deduced from the response of a suitable detector. Detectors which respond to physicochemical properties other than concentration may also be of use in GPC. Over the past 25 years, a variety of detectors have been developed. This section reviews detectors available to the chromatographer. The detectors used in GPC can be grouped as... 

Typical 19F chemical shifts for u-CnH2n+1CF2H compounds are between -116 and -117 ppm, with the usual branching effects being observed. Thus, a CF2H group attached to a secondary carbon is more shielded (7-10ppm), and one attached to a tertiary carbon is still farther upheld. 

Some doubt is thrown on B strain as the sole explanation of the branching effect by the observation that the tri-te -butylboron-ammonia complex is actually less dissociated than the trimethylboron-ammonia complex.227 Since the products of the ionization of these highly branched compounds contain large amounts of rearranged material, another effect may be operating. As will be discussed in the next section, many ionization reactions produce directly an ion of structure different from that of the covalent parent compound. The transition state presumably resembles the new ion or a non-classical... 

The decrease in [rj] due to contraction as a result of branching is now no longer compensated by performing the number average over the ensemble distribution. Thus the branching effect here becomes apparent also for the non-fraction-ated samples. 

Branching effects of polyvinyl acetate (PVAc) were... 

Branching effects in PE [OLEFIN POLYMERS - POLYETHYLENE - HIGH DENSITY POLYETHYLENE] (Vol 17)... 

Solvent tends to attenuate the a-branching effect in Sj,f2 reactions (see Table 6.6). The gas-phase barrier increases twice as rapidly with the addition of each methyl group compared to that in acetone. Jensen" performed B3LYP/6-31-I-G optimizations of the reactants and TSs in the gas phase and then obtained free energies in water using the polarized continuum mediod (PCM). These results are also listed in Table 6.6. The gas-phase computational values match up well with the experimental values. However, the relative activation barriers computed with PCM are quite similar to the gas-phase values and, therefore, overestimate the solution-phase barriers. 

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