Double-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... 

Note Cd = double-bonded carbon Ct = triple-bonded carbon Ca = allenic carbon. Corrections are also provided for non-nearest-neighbor interactions, such as for cis isomers, gauche conformers, and ring systems. (See Note 4.)... 

It is likely that one of the major mechanistic requirements for a good enhancer is the ability to induce some sort of motional freedom in the alkyl-chain region of lipid bilayers. Azone appears to be capable of this. These lipid-chain molecular motions may lead to the easier formation of gauche conformers and thus create a greater number of lipid free volumes. Creation of such free volumes has already been associated with greater skin permeability (Potts et al., 1991), and the positive relationship between molecular size of penetrant and rate of permeation is well established. The action of OA may occur in a similar manner but, because of its longer chain, which impedes adjacent lipid chain motion, to a lesser extent. It is likely that the large kink in the OA molecule created by its cis double bond is an important structural feature in its ability to act in this manner (stearic acid seems to condense DPPC monolayers). 

The vinylcyclopropane chromophore takes an exceptional position among the compounds in which a double bonded group is linked to the cyclopropane ring. In the parent molecule, vinylcyclopropane (127), there is a s-trans-gauche conformational equilibrium whereas in all other related double bonded compounds (acids, aldehydes, etc.) s-trans and s-cis conformers are preferred... 

From the above results (Schemes 42-44), it appears that trans- and cis-cyclohexane-1,2-diamines (t-chxn and c-chxn) or gauche 1,2-diamines are useful linkers for preparing double salts of unusual photoreactivity. Evidently, photore-active overlap configurations are more likely to happen to the gauche conformation of 1,2-diamine. There are, however, limitations. For example, the double salt 9-AP ( )-t-chxn, which crystallized with 1 mol of included MeOH, yielded virtually no head-to-head dimer but only a small yield of the usual head-to-tail dimer of 9-AP [76]. 

In allyl fluoride the fluorine eclipses the double bond, but in allyl chloride and bromide the gauche conformations are preferred to the extent of 82 and 95% respectively (Schei and Shen, 1985 Schei, 1983). In a-haloacid halides, such as chloroacetyl chloride, analogous conformations with the halogen atom eclipsed by the carbonyl have been found to be the most stable conformer (Nakagawa et al., 1952). The energy difference between s-tram... 

Potential impact of rotator phase on crystallization. Molecular dynamics simulations have been carried out to study the conformational defects in the orientationally ordered structures of short-chain molecules and polymer chains. The simulation showed the creation of orientationally ordered structures from a random coil configuration by cooling from the melt. The longer chains exhibit folding with double gauche defects with the same sign ( tg( + )g( + )t. . . ) predominantly located at the chain ends and the kink... 

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