End-gauche conformers

An FTIR comparison between C18 and C30 sorbents prepared by both surface-and solution-polymerized synthetic routes over a range of temperatures was recently described [119]. Little difference in conformational order was observed for C30 sorbents prepared by both surface and solution-polymerized synthetic routes, as indicated by kink/gfg, double- and end-gauche conformations. Differences in conformational... 

The notation of Maroncelli et al. (20,21) will be followed in discussing conformation, so that, in our designation of the conformational state of a CD2 group, the CC bonds that are directly bonded to the CD2 group will be underlined. Thus t means the CD2 moiety connects a trans and a gauche bond. End-gauche conformations... 

Higher alkanes having unbranched carbon chains are like butane most stable m then-all anti conformations The energy difference between gauche and anti conformations is similar to that of butane and appreciable quantities of the gauche conformation are pres ent m liquid alkanes at 25°C In depicting the conformations of higher alkanes it is often more helpful to look at them from the side rather than end on as m a Newman projec tion Viewed from this perspective the most stable conformations of pentane and hexane... 

For all the temperatures studied, the simulations lead to crystalline monolayers with strong orientational ordering of the chains in a distorted hexagonal structure even in the absence of an applied pressure. The chains are tilted at an angle of 30° to the surface normal. Most of the gauche defects are found near the ends of the chains, as observed in crystals of n-alkanes, but even at 400 K the average number of gauche conformations per chain is only about one. 

It has been revealed by X-ray studies106,107) that in polyethylene the carbon-carbon bond distance is 1.54 A and the valence angle 108°, suggesting that the carbon atom in the polymer chain is tetrahedral. As all of the polyolefins including polyethylene possess helical coiled structure, the tetrahedral stereochemistry for the carbon atom in the polymer chain would persist in all of them. With bulky pendant groups linked to the polymer chain, this tetrahedral structure is most likely to be under considerable strain. For example, polyethylene, through a carbon-carbon bond scission in the polymer chain, forms the radical (XV) in which the unpaired electron and two C-H bonds on CH are in trans or gauche conformation with the two C 2-H bonds and the C T-Cn bond. The radical end... 

Thermal stability. Vox applications of LB films, temperature stability is an important parameter. Different techniques have been employed to study this property for mono- and multilayers of araehidate LB films. In general, an increase in temperature is connected with a conformational disorder in the films and above 390 K the order present in the films seems to vanish completely [45, 46 and 47]. However, a eomprehensive picture for order-disorder transitions in mono- and multilayer systems cannot be given. Nevertheless, some general properties are found in all systems [47]. Gauche conformations mostly reside at the ends of the ehains at room temperature, but are also present inside the... 

In the structure obtained at the end of the simulation the chains were ordered in an approximately hexagonal pattern. During equilibration gauche conformations were introduced into the alkyl chains, causing the system to tilt. However, once the molecules had all tilted the... 

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