Hydrogen–Hydrogen Bonds in Highly Branched Alkanes and in Alkane Complexes: A DFT, ab initio, QTAIM, and ELF Study

The hydrogen–hydrogen (H–H) bond or hydrogen–hydrogen bonding is formed by the interaction between a pair of identical or similar hydrogen atoms that are close to electrical neutrality and it yields a stabilizing contribution to the overall molecular energy. This work provides new, important information regarding hydrogen–hydrogen bonds. We report that stability of alkane complexes and boiling point of alkanes are directly related to H–H bond, which means that intermolecular interactions between alkane chains are directional H–H bond, not nondirectional induced dipole–induced dipole. Moreover, we show the existence of intramolecular H–H bonds in highly branched alkanes playing a secondary role in their increased stabilities in comparison with linear or less branched isomers. These results were accomplished by different approaches: density functional theory (DFT), ab initio, quantum theory of atoms in molecules (QTAIM), and electron localization function (ELF).