Retention Indices of Adamantanes

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Abstract
Retention indices were obtained for 31 adamantane hydrocarbons on squalane, Apiezon L and tetrakis-O-/2-cyanoethyl/-pentaerythritol at five temperatures in the range of 110° to 200°C. Some relationships between chemical structure and retention were found. Substitution on the secondary carbon atom of the adamantane nucleus influences retention in a manner different from that of substitution on the tertiary carbon atom. Analogous substitution of methyl groups on adamantane and diamantane causes almost the same change of the retention index. An increasing number of substituents on bridgehead positions of the adamantane nucleus decreases retardation with respect to the corresponding n-alkane. In comparison with squalane total inversion of the elution order of bridgehead methyladamantanes take place on the polar stationary phase used. Values of ΔI for bridgehead-substituted methyl- and ethyl-adamantanes may be calculated from the increments. The plot of retention indices of these derivatives on the polar and nonpolar stationary phase forms a regular lattice-type graph which enables prediction of the retention indices. The number of cycles in molecules of non-substituted adamantanoid hydrocarbons thus influences the value of ΔI as well as the magnitude of variation of the retention index with the column temperature.

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