title: Charge-density analysis using multipolar atom and spherical charge models: 2-methyl-1,3-cyclopentanedione, a compound displaying a resonance-assisted hydrogen bond.
abstract: The experimental charge-density distribution in 2-methyl-1,3-cyclopentanedione in the crystal state was analyzed by synchrotron X-ray diffraction data collection at 0.33 Å resolution. The molecule in the crystal is in the enol form. The experimental electron density was refined using the Hansen-Coppens multipolar model and an alternative modeling, based on spherical atoms and additional charges on the covalent bonds and electron lone-pair sites. The crystallographic refinements, charge-density distributions, molecular electrostatic potentials, dipole moments and intermolecular interaction energies obtained from the different charge-density models were compared. The experimental results are also compared with the theoretical charge densities using theoretical structure factors obtained from periodic quantum calculations at the B3LYP/6-31G** level. A strong intermolecular O-H···O hydrogen bond connects molecules along the [001] direction. The deformation density maps show the resonance within the O=C-C=C-OH fragment and merged lone pair lobes on the hydroxyl O atom. This resonance is further confirmed by the analysis of charges and topology of the electron density.
authors.affiliation: Laboratoire de Cristallographie, Résonance Magnétique et Modélisations, CNRS UMR 7036, Université de Lorraine, BP 70239, 54506 Vandoeuvre-les-Nancy CEDEX, France.
authors.forename: Ayoub
authors.initials: A
authors.lastname: Nassour
authors.affiliation: Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznań, Poland.
authors.forename: Maciej
authors.initials: M
authors.lastname: Kubicki
authors.affiliation: European Synchrotron Radiation Facility (ESRF), 6 Rue Jules Horowitz, BP 220, 38043 Grenoble CEDEX 9, France.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Wright
authors.affiliation: Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznań, Poland.
authors.forename: Teresa
authors.initials: T
authors.lastname: Borowiak
authors.affiliation: Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznań, Poland.
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Dutkiewicz
authors.affiliation: Laboratoire de Cristallographie, Résonance Magnétique et Modélisations, CNRS UMR 7036, Université de Lorraine, BP 70239, 54506 Vandoeuvre-les-Nancy CEDEX, France.
authors.forename: Claude
authors.initials: C
authors.lastname: Lecomte
authors.affiliation: Laboratoire de Cristallographie, Résonance Magnétique et Modélisations, CNRS UMR 7036, Université de Lorraine, BP 70239, 54506 Vandoeuvre-les-Nancy CEDEX, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Jelsch
keywords: bond scatterers; electron lone pairs; resonance-assisted hydrogen bond; virtual atoms model; β-diketoalkanes