Frans-fatty acids, structure

Structural features in unsaturated fatty acid methyl esters (in carbon tetrachloride solution) can give rise to distinctive bands in Raman spectroscopy [208-210]. For example, characteristic Raman bands are found for c s-double bonds (1656 cm ), frans-double bonds (1670 cm ) and triple bonds (2232 and 2291 cm ) a terminal triple bond gives a single band at 2120 cm (this group does not give a distinctive band in IR spectroscopy). Again, the position of a double bond does not affect the spectrum significantly unless it is at either extremity of the molecule. 

GC-MS. For example, branched-chain primary alcohols have been oxidised to the corresponding acids and methylated for analysis, since the mass spectra of methyl esters are well documented [424,426], Others prepared pyrrolidides, after oxidation to the acids, as these give spectra which are more readily interpreted [46], Similarly, secondary alcohols have been oxidised to ketones as an aid to identification [113], Double bonds in alkyl chains of alcohols have been located by MS after the preparation of suitable chemical adducts, similar to those described for fatty acids in Chapter 7. Oxidation to diols and conversion to the TMS ethers is one method [638], but synthesis of dimethyl disulfide adducts from alcohol acetates is a one-step reaction (see Chapter 4) and is now preferred [143,540], On the other hand, it may be too much to expect that a single method will provide all the information desired on a given sample it required partial hydrogenation, coupled with GC-MS and GC/Fourier-transform IR (to identify frans-double bonds), to determine the structure of a trienoic insect trail pheromone [1006],... 

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