Formation of a -Complex with Ag Ions

The number of double bonds present in an oil or fat can be determined through their iodine number (cf. 14.5.2.1). The fat or oil is treated with a halogen reagent which reacts only with the double bonds. Substitution reactions generating hydrogen halides must be avoided. IBr in an inert solvent, such as glacial acetic acid, is a suitable reagent  

Unsaturated fatty acids or their triacylglycerols, as well as unsaturated aldehydes obtained through autoxidation of lipids (cf. 3.7.2.1.5), can be separated by argentation chromatography . The separation is based on the number, position and configuration of the double bonds present. The separation mechanism involves interaction of the r-electrons of the double bond with Ag ions, forming a reversible TT-complex of variable stability  

The number of double bonds is calculated by titrating the unreacted IBr reagent with thiosulfate. 

2 Transformation of Isolene-Type Fatty Acids to Conjugated Fatty Acids 

Allyl systems are labile and are readily converted to a conjugated double bond system in the presence of a base (KOH or K-tertbutylate)  

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