17α,21α(H)-hopanes: Natural and synthetic

17α,21α(H)-hopanes are found in low concentrations in sediments and oils, but C₃₀ 17α,21α(H)-hopane is the only member of the series which can be detected in the m/z 191 mass chromatogram. The ratio of C₃₀ 17α,21α(H)-hopane to C₃₀ 17α,21β(H)-hopane is typically 0.02-0.04 in crude oils and mature sediments. Ratios up to 0.10 have been found in immature sediments with 22S/(22S + 22R) ratios of C₃₁-C₃₅ hopanes around 0.4. Compounds coeluting with 17α,21α (H)-hopane are usually absent in samples of early oil window rank or higher maturity. 17α,21α(H)-hopane and 17α,21β (H)-hopane have almost identical mass spectra and response factors in the m/z 191 mass chromatogram. These features make 17α,21α(H)-hopane an ideal internal standard for the quantification of hopanes in oils and sediments. 17α,21α(H)-hopane can be obtained in high yield by hydrogenation of synthetic hopa-15,17(21)-diene.