Estimation of various chemical bond dissociation enthalpies of large-sized kerogen molecules using DFT methods

<p>Kerogen is irregularly connected by a variety of chemical bonds including C–C bond, C=C bond, C–O bond, C–N bond, C–H bond and C–S bond. It is difficult to identify selective bond breaking events using the existing experimental conditions. In this study, we predict dissociation tendencies of chemical bonds in various kerogen molecules by using 554 small molecular model compounds based on the density functional theoretical (DFT) calculations. Results from our DFT study indicate that the calculated various subtypes of bond dissociation enthalpies (BDEs) changing tendency is that C–S bond < C–N bond < C–O bond < C–C bond < C–H bond < C=C bond. However, for each bond type, the BDE value has a large range and overlaps each other, and the BDE mostly relies on the local environment (the functional groups and position) of chemical bonds and radical stability. For the C–C bond, a linear relationship (<i>R</i> = 0.85) between C–C bond distances and BDE has been achieved. Thus, the bond distance can serve as a good indicator of bond strength for C–C bond linkages. All results support that the BDE is a good choice to evaluate the dissociation tendencies of kerogen and this work provides an effective path to reveal the nature of chemical bonding for large-sized kerogen molecules.</p>