Alkanes tetracyclic—

Some tri- and tetracyclic alkanes contain two cyclopropane moieties locked into a fixed orientation. These arrangements might give rise to interesting stereoelectronic effects in the interaction between the cyclopropane rings. For example, CIDNP effects during electron-transfer reactions of syn- and a/jn -tricyclo[5.1.0.0 ]octane syn-, anfi-89) indicate significantly different structures for their radical cations. 

Disnar J.R., Harouna M. (1994) Biological origin of tetracyclic diterpanes, ft-alkanes and other biomarkers found in Lower Carboniferous Gondwana coals (Niger). Org. Geochem. 21, 143—52. 

What kind of structure might we predict for benzene if we knew only what the early chemists knew The molecular formula (CgHg) tells us that benzene has eight fewer hydrogens than an acyclic (noncyclic) alkane with six carbons (C H2 +2 = C6H14). Benzene, therefore, has a degree of unsaturation of four (Section 3.1). This means that benzene is either an acyclic compound with four tt bonds, a cyclic compound with three tt bonds, a bicyclic compound with two tt bonds, a tricyclic compound with one TT bond, or a tetracyclic compound. 

In contrast, Figure 6 also shows cross plots of normal and isoprenoid alkane and tetracyclic alkane parameters for the end member oils and... 

Fig. 6. Acyclic alkane, hopane and tetracyclic alkane cross plots of end member oils A and B and mixtures of each. Red squares are selected end member oils red circles represent calculated mixtures of oils A and B in 10% increments. Definition of ratios %35ab= 100 x S R C35 homohopane/(S R C34 homohopane + S R C35 homohopane) %24/4= 100 x C24 tetracyclic terpane/(C24 tetracyclic terpane + C23 tricyclic and C25 tricyclic terpane). Note that for the acyclic alkanes which have similar concentration ranges the mixing curve is essentially linear, whereas for the cyclic biomarkers with very different end member concentrations, the mixing curve is distinctively nonlinear. In this illustrative case of course the actual variations in %24/4 are not sensibly interpretable.

Two groups of tetracyclic and pentacyclic alkanes, steranes and hopanes, respectively, are presented schematically in Figures 27 and 28. The analysis of these biomarkers requires the optimal combined techniques of GC and MS, as well as a large memory and fast computers. The application of the GC/MS/C analysis of steranes and hopanes in petroleum geochemistry was extensively studied and reviewed Most of the... 

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