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The electron density of 4-methyl-[4]helicene is analyzed with an emphasis on the fjord region as metabolic activation is initiation in this region. The analysis has shown that the highly twisted nature of helicenes have entailed the appearance of a weak closed-shell hydrogen-hydrogen (H-H) bonding interaction in the fjord region of the molecule.

The electron density and the electrostatic potential (ESP) distributions of estrone is determined using X-ray diffraction analysis and the theoretical calculations in the solid and gas phases are compared. It is observed that the electron density in the estrone crystal is described with the multiple model, which allows extensive topological and calculation of the ESP.

A report is presented on several weak interactions in nucleic acids, which collectively can make a noneligible contribution to the structure and stability of these molecules. A study characterizes the pi-stacking interaction between the nearest neighbor stacked bases, the interactions that a given nuclease has with the backbone and the interactions within the backbone itself.

The ubiquity of the fluorine-fluorine bonding interaction for a systematic examination is reported. Teh bond path is shown to persist for a range of internuclear distances (2.3-2.8 angstrom) and a range of relative orientations of the two C-F internuclear axes.

The charge on an atom in a molecule is defined by the quantum theory of atoms in molecules (QTAIM) as the expectation value of the number operator, a Dirac observable. An atom charge is measurable and together with its change contributes to numerous measurable properties to all molecular moments, to molecular polarizability, to intensities of electronic, infrared, and Raman absorption intensities, and to the polarization of a dielectric.

The domination of the Fermi contact term in the spin-spin coupling of protons is examined. NMR experiments are used for this purpose.

Research has been conducted on the crystalline compound containing titanium that bonds to cyclopentadienyl and a substituted dienyl fragment. The synthesis of this compound has been carried out in investigating the titanium-carbon contacts and the results are reported.

The view stating that the concept of an atom in a molecule, is an object knowable by the mind or intellect, not by the senses is countered by the two hundred years of experimental chemistry underlying the realization that the properties of some total system are the sum of its atomic contributions. It is found that an experimentalist has no doubt, about measuring the properties of atoms when performing an experiment.

The delocalization indices are calculated within the framework of the quantum theory of atoms in molecules and it provides an excellent basis for the definition of a bond order in polycyclic aromatic hydrocarbons. It is demonstrated that two-electron information contained within the delocalization index can be estimated from the electron density at the bond critical point.

We employ second-order Møller-Plesset perturbation theory level in combination with recently developed pseudopotential-based correlation consistent basis sets to obtain accurate relativistic-consistent electron densities for small coinage metal clusters. Using calculated electron densities, we employ Bader's quantum theory of atoms in molecules (QTALM) to gain insights into the nature of metal-metal bonding in the clusters M2, M4, M4,2-, and M4Na2 (M = Cu, Ag, Au). For the simplest case of the metal dimer, M2, we correlate the strength of the metal-metal bond with the value of the electron density at the bond critical point, the total energy density at the bond critical point, the sharing (derealization) index, and the values of die two principle negative curvatures. We then consider changes to the metal-metal bonding and charge density distribution upon the addition of two metal atoms to form the metal tetramer, M4 and then followed by the addition of an electron pair to form M42- and finally followed by die addition of two alkali metal (sodium) ions to form M4Na2. Using topological properties of die electron density, we present evidence for the existence of a-aromaticity in Au42- . We also report die existence of two non-nuclear attractors in the molecular in the molecular graph of Cu42- and large negative charge accumulation in the nonbonded Cu basins of this cluster. [ABSTRACT FROM AUTHOR]

Professor Dunitz questions the usefulness of ascribing crystalline structural stability to individual atom-atom intermolecular interactions viewed as bonding (hence stabilizing) whenever linked by a bond path. An alternative view is expressed in the present essay that articulates the validity and usefulness of the bond path concept in a crystallographic and crystal engineering context.