Structural characterization of Saudi Arabian extra light and light crudes by ¹H and ¹³C n.m.r. spectroscopy

A study of distillate fractions of Saudi Arabian light and extra light crudes by ¹H and ¹³C n.m.r. spectroscopy describes average composition of these crudes. The ¹H n.m.r. spectra of six distillate fractions indicates an increase in chain length of paraffins and of alkyl groups attached to aromatic rings. Similarly more of the aromatic carbons are substituted with alkyl and methyl groups in the high boiling fractions. ¹³C n.m.r. spectra show that the percentage of paraffins decreases sharply with fractionation resulting in an increase in percentage of aromatic carbons in both crudes. Moreover as also indicated by ¹H n.m.r. spectra, the paraffinic chains are of shorter length in the earlier fractions and of longer length in the later fractions. The distribution of aromatic carbons, bearing alkyl groups and of bridgehead carbons also increases with fractionation. The average structure of compounds present in both the Saudi Arabian light and extra light crudes are surprisingly similar.