Trans bonds INDEX

For trans double bonds "X. = 0 and X., = X, but for cis double bonds the index X,. is smaller than X, achieving thereby a differentiation between TIs of cis/trans diastereomers. Index X, is linearly related to Randic s XX index ... 

Fig. 10.4. The staggered, normalized bond dimerization, S , (defined in eqn (4.27)) as a function of bond index from the centre of the chain of various states of trans-polyacetylene calculated from the Pariser-Parr-Pople-Peierls model. 1 A+ (crosses), (squares), 1 5 (triangles), 2 (diamonds) andpolaron (circles).

The columns are indexed by the three states of bond i, the rows are indexed by the three states of bond i—1, and the order of indexing is t, g+, g. The statistical weight denoted by cr, which is approximately exp (-250/T), is the first-order weight of a gauche state relative to a trans state. The second-order interaction, which arises from the pentane effect where a bond pair is g gT, is weighted by to, which is approximately exp (-1000/T). 

Photorefractivity is a property exhibited by some materials in which the redistribution in space of photogenerated charges will induce a nonuniform electric space-charge field which can, in turn, affect the refractive index of the material. In a new material the active species is a highly efficient cyclopalladated molecule97,98 shown in Figure 5. The palladium-bonded azobenzene molecule is conformationally locked, and gratings derived from cis—trans isomerizations can be safely excluded. 

The butanolide and butenolide lactones are formally furans with exocyclic double bonds and are sometimes indexed in this manner. Their chemistry, however, is not customarily related to furan chemistry but simply to acyclic ester chemistry. Lactones of course have the CC-cis rather than the CC-trans conformation (36JCS1383), but the atoms defining the... 

The physical properties, such as melting points, specific heat, viscosity, density, and refractive index depend on the type of fatty acids present in the triglyceride and their location, chain length of fatty acids, number and location of cis and trans double bonds on the fatty acid chains as well as compatibility of the different triglycerides in the mixture and the type of crystal present. 

A third backbone index trans was defined by Equation 12.24, as the number of carbon-carbon double bonds along the chain backbone which are in a trans configuration divided by the number NBB of backbone atoms. If there is a mixture of cis and trans isomerization around the C=C bonds along the chain backbone, only the trans double bonds are counted. For example, all-trans polyisoprene has one trans C=C backbone bond per repeat unit with NBB=4, so that... 

Composition of oil/fat. To study the composition of oil/fat it is essential to test the purity of an oil/ fat for adulteration, accidentally or voluntarily. The specific fatty acid in fat can be determined by GC by preparing methyl esters with sodium methoxide. Mass spectrometry coupled to GC (GC-MS) is the most powerful tool for identification of fatty acids separated by GC. Free fatty acids in oil (index of rancidity) can be determined by titration against standard alkali. Infrared (IR) spectroscopy, Raman spectroscopy, and ultraviolet (UV) spectroscopy (200—400 nm) are used to detect isomers (trans and cis) of unsaturated fatty acids and conjugated double bonds. It is important to study saponification value (depict fatty acid chain length), iodine value (give the degree of unsaturation), and hydroxyl value (free fatty acids present in fats). 

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