A study of petroleum alkylcarbazoles using 1H NMR spectroscopy

A precision method for measuring proton chemical shift calculations of methylcarbazoles has been developed. For other abundant substituents the proton chemical shift correlation diagrams are reported. The method makes it possible to identify a number of carbazole structures present in petroleums. General structural regularities of petroleum carbazoles have been defined from 1H NMR data. Methylcarbazole isomers with 1- and 1,8-substituents were found to be most abundant in crude oils. Structures with three or more adjacent Me-groups and with substituents in both 4,5-positions are absent. The distribution of methyl substituents is likely to be controlled partly by migration processes. On the other hand the distribution of non-methyl substituents is of a different character and can vary with chain length.