Reactivities of Aromatic Protons in Crude Oil Fractions toward Br2 Tagging for Structural Characterization by Nuclear Magnetic Resonance and Electron Paramagnetic Resonance Spectroscopy and Mass Spectrometry

Comprehensive characterization and structural elucidation of specific chemical subclasses within a complex mixture often require analyte separation, a variety of spectroscopic techniques, and inquiry into reactivity patterns. Crude oil is one of the most challenging and highly complex mixtures, and for classification purposes, it is typically separated into low-weight n-heptane-soluble and high-weight toluene-soluble (or asphaltene) fractions. Both fractions of crude oil have been studied previously using various spectroscopic methods, but their complete characterization remains elusive. In this work, we use selective functional group derivatization of both n-heptane and asphaltene fractions of crude oil for unprecedented identification of chemical functional groups by a combination of high-resolution mass spectrometry, H-1 and C-13 nuclear magnetic resonance, and electron paramagnetic resonance spectroscopy methods. Chemical tagging with elemental bromine suggests that the aromatic protons within the asphaltene fraction are less abundant and more sterically hindered than previous models might suggest. An efficient column purification Was used to remove paramagnetic metals and allow for the identification of crude oil functional groups via analysis of spectrometry and spectroscopy data combined with chemical reactivity studies.