Article

CH/pi interaction between benzene and model neutral organic molecules bearing acid CH groups

New Journal of Chemistry (Impact Factor: 2.97). 01/2002; 26:1718-1723. DOI: 10.1039/B208432E

ABSTRACT To explore the binding properties of benzene towards small molecules bearing C H groups with different acidities, we have undertaken ab initio quantum-chemical calculations, including correlation effects through Density Functional Theory methods, on the benzene CH3X (X = F, Cl, Br, I, CN, NO2) adducts. Benzene acts as a Lewis base and the CH3X molecule as a Lewis acid. The partial charge transferred from benzene to the Lewis acid is mainly confined on the X group and increases with the electron withdrawing character of X. The calculations performed on the various systems predict that two different stable structures for each adduct exist: one with C-3v and the other with C-s symmetry, the latter being the most stable one. A simple HOMO-LUMO model suggests that the charge is transferred from the benzene HOMO to the CH3X LUMO and that this process is easier in the systems with C-s symmetry due to the better overlap between the frontier orbitals.

0 Bookmarks
 · 
85 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Geometries and interaction energies for methane clusters with naphthalene and pyrene were studied. Estimated CCSD(T) interaction energies for the clusters at the basis set limit were -1.92 and -2.50 kcal mol(-1), respectively. Dispersion is mainly responsible for the attraction. Electrostatic interaction is very small. Although the benzene-methane cluster prefers a monodentate structure, in which a C-H bond of the methane points toward the benzene, the methane clusters with the polycyclic aromatic hydrocarbons do not prefer monodentate structures. In the benzene-methane cluster, the weak electrostatic interaction stabilizes the monodentate structure. On the other hand the dispersion interaction controls the orientation of methane in the naphthalene and pyrene clusters. The dispersion interactions in these clusters are significantly larger than those in the benzene-methane cluster. The methane prefers the orientation which is suitable for stabilization by dispersion. Hydrogen atoms of the methane locate above the centers of hexagonal rings of the polycyclic aromatic hydrocarbons in the stable structures. The structures have a small steric repulsion and this positions them only a short distance from the aromatic plane. The large dispersion contribution to the attraction shows that interactions between carbon atoms are mainly responsible for the attraction, and that hydrogen atoms are not important for the attraction. This shows that the interactions between the methane and polycyclic aromatic hydrocarbons are not pi-hydrogen bonds.
    Physical Chemistry Chemical Physics 06/2008; 10(19):2860-5. · 3.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Recently reported high-level ab initio calculations and gas phase spectroscopic measurements show that the nature of CH/pi interactions is considerably different from conventional hydrogen bonds, although the CH/pi interactions were often regarded as the weakest class of hydrogen bonds. The major source of attraction in the CH/pi interaction is the dispersion interaction and the electrostatic contribution is small, while the electrostatic interaction is mainly responsible for the attraction in the conventional hydrogen bonds. The nature of the "typical" CH/pi interactions is similar to that of van der Waals interactions, if some exceptional "activated" CH/pi interactions of highly acidic C-H bonds are excluded. Shifts of C-H vibrational frequencies and electronic spectra also support the similarity. The hydrogen bond is important in controlling structures of molecular assemblies, since the hydrogen bond is sufficiently strong and directional due to the large electrostatic contribution. On the other hand, the directionality of the "typical" CH/pi interaction is very weak. Although the "typical" CH/pi interaction is often regarded as an important interaction in controlling the structures of molecular assemblies as in the cases of conventional hydrogen bonds, the importance of the "typical" CH/pi interactions is questionable.
    Physical Chemistry Chemical Physics 06/2008; 10(19):2584-94. · 3.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This treatise is an update to a preceding highlight (CH/π hydrogen bonds in crystals) published in this journal 5 years ago (M. Nishio, CrystEngComm, 2004, 6, 130–156). After the introductory part (sections 1 and 2), we survey recent results (mostly since 2004) relevant to the CH/π hydrogen bond: crystal conformation, packing and host/guest chemistry (section 3). Section 4 summarizes the results obtained by crystallographic database (CSD and PDB) analyses. In section 5, several topics in related fields (selectivity in organic reactions, surface chemistry, structural biology, drug design and high-level ab initio calculations of protein/substrate complexes and natural organic compounds) are introduced, and in the final part we comment on the prospects of this emerging field of chemistry.
    CrystEngComm 01/2009; 11(9). · 3.88 Impact Factor