Methoxy groups, analytical determination

One of the most important parameters for weU separation of flavonoids is the composition of the eluent. Controlling the solubility of the flavonoids in the eluent is a cmcial factor for determining the combinatimi of solvents used. In RP-HPLC, analytes are retained on the stationary phase based on their hydrophobicity. Elution of flavonoids in RP-HPLC is therefore in the order of decreasing polarity. Polarity increases most by hydroxyls at the fourth position, followed by those at the second and third positions. Loss of polar hydroxyl groups or additions of methoxy groups reduce polarity and hence increase retention times. 

In the p-alkoxyphenyl esters of cyclohexanedicarboxylic acid, the series was prepared and thermally examined in which the alkoxy group was varied from methoxy through hexyloxy The thermal properties and analytical results for this series are listed in Table 1. The first two members of the series have only nematic mesophases, while the propoxy through the hexyloxy have both nematic and smectic phases As the length of the alkyl tail increases, so does the complexity of the transitions There are four distinct solid polymorphs in the pentyloxy and three in the hexyloxy compound The hexyloxy also has three smectic phases as well as the nematic These three transitions were identified as smectic by microscopy, however no attempt was made to assign them to a particular class The heats of two of these transitions were too small to measure with any degree of accuracy and only the temperatures were recorded Solid polymorphism, such as encountered in these compounds where the transitions occur at very close temperatures, prevents the application of the differential scanning calorimetric method for determination of purity ... 

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