Gauche/trans ratio

Yoshino (51) studied the abundance ratios of the gauche and trans forms of dichloroethane and the keto-enol isomers of acetyl acetone when these compounds were adsorbed (less than monolayer quantities) on silica gel. The gauche-trans ratio, which is unity in chloroform solution and 1.4 in the pure liquid, was found to be 1.9 in the adsorbed state. The 1430-cm.-1 gauche band and the 1450-cm.-1 trans band were not affected by the adsorption. The absorption bands of acetyl acetone were measured for a 1.5 % chloroform solution, the pure liquid, liquid saturated with water, and the adsorbed state. The relative intensity of the 1600-cin. 1 enol band and the 700-cm.-1 keto baud were used to determine the isomer ratio. The 1600-... 

At low temperatures, in lipid bilayers prepared from a single lipid species, the acyl/alkyl chains of the lipids in the bilayer are characterized by a high trans/gauche configurational ratio. 

The validity of the computed equilibria is substantiated by the experimental cis/trans ratios for the three positional isomers of dimethyl-cyclohexane, measured at ambient temperature by Roebuck and Evering (42) and at 175° by Boelhouwer et al. (43). The experimental results, presented in Table II, are in excellent agreement with theoretical equilibria that were computed on the basis of 1.0 kcal per gauche interaction. 

Fig. 11. Comparison between the PE spectrum of bicyclopropyl and calculated orbital energies according to the ZDO mode with 20% admixture of radial contributions. A ratio of gauche/trans of 60 40 is assumed...

With all-atom simulations the locations of the hydrogen atoms are known and so the order parameters can be calculated directly. Another structural property of interest is the ratio of trans conformations to gauche conformations for the CH2—CH2 bonds in the hydrocarbon tail. The trans gauche ratio can be estimated using a variety of experimental techniques such as Raman, infrared and NMR spectroscopy. 

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