title: Dihydrogen contacts in alkanes are subtle but not faint.
abstract: Alkane molecules are held together in the crystal state by purportedly weak homonuclear R-H···H-R dihydrogen interactions. In an apparent contradiction, the high melting points and vaporization enthalpies of polyhedranes in condensed phases require quite strong intermolecular interactions. Two questions arise: 'How strong can a weak C-H···H-C bond be?' and 'How do the size and topology of the carbon skeleton affect these bonding interactions?' A systematic computational study of intermolecular interactions in dimers of n-alkanes and polyhedranes, such as tetrahedrane, cubane, octahedrane or dodecahedrane, showed that attractive C-H···H-C interactions are stronger than usually thought. We identified factors that account for the strength of these interactions, including the tertiary nature of the carbon atoms and their low pyramidality. An alkane with a bowl shape was designed in the search for stronger dihydrogen intermolecular bonding, and a dissociation energy as high as 12 kJ mol⁻¹ is predicted by our calculations.
authors: Departament de Química Inorgànica and Institut de Química Teòrica i Computacional, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
authors: Jorge
authors: J
authors: Echeverría
authors: Gabriel
authors: G
authors: Aullón
authors: David
authors: D
authors: Danovich
authors: Sason
authors: S
authors: Shaik
authors: Santiago
authors: S
authors: Alvarez
mesh_terms: D000218:Adamantane / Q000737:chemistry; D000473:Alkanes / Q000737:chemistry*; D001372:Aza Compounds / Q000737:chemistry; D001952:Bridged-Ring Compounds / Q000737:chemistry; D002073:Butanes / Q000737:chemistry; D055598:Chemical Phenomena; D003198:Computer Simulation; D003461:Crystallography; D003516:Cycloparaffins / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D008697:Methane / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011083:Polycyclic Compounds / Q000737:chemistry; D013816:Thermodynamics; D044366:Transition Temperature
chemical_list: D000473:Alkanes; D001372:Aza Compounds; D001952:Bridged-Ring Compounds; D002073:Butanes; D003516:Cycloparaffins; D037741:Fullerenes; D011083:Polycyclic Compounds; C516928:octahedrane; C062580:dodecahedrane; D006859:Hydrogen; D008697:Methane; D000218:Adamantane