title: Charge density of the biologically active molecule (2-oxo-1,3-benzoxazol-3(2H)-yl)acetic acid.
abstract: (2-Oxo-1,3-benzoxazol-3(2H)-yl)acetic acid is a member of a biologically active class of compounds. Its molecular structure in the crystal has been determined by X-ray diffraction, and its gas phase structure was obtained by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory. In order to understand the dynamics of the molecule, two presumably soft degrees of freedom associated with the relative orientation of the planar benzoxazolone system and its substituent at the N atom were varied systematically. Five conformers have been identified as local minima on the resulting two-dimensional potential energy surface within an energy window of 27 kJ mol(-1). The energetically most favourable minimum closely matches the conformation observed in the crystal. Based on high-resolution diffraction data collected at low temperature, the experimental electron density of the compound was determined. Comparison with the electron density established by theory for the isolated molecule allowed the effect of intermolecular interactions to be addressed, in particular a moderately strong O-H...O hydrogen bond with a donor...acceptor distance of 2.6177 (9) Å: the oxygen acceptor is clearly polarized in the extended solid. The hydrogen bond connects consecutive molecules to chains, and the pronounced charge separation leads to stacking between neighburs with antiparallel dipole moments perpendicular to the chain direction.
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Aachen, Germany.
authors.forename: Ai
authors.initials: A
authors.lastname: Wang
authors.affiliation: Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Uzbekistan.
authors.forename: Jamshid
authors.initials: J
authors.lastname: Ashurov
authors.affiliation: Institute of General and Inorganic Chemistry, Academy of Sciences of Uzbekistan, Uzbekistan.
authors.forename: Aziz
authors.initials: A
authors.lastname: Ibragimov
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Aachen, Germany.
authors.forename: Ruimin
authors.initials: R
authors.lastname: Wang
authors.affiliation: Institute of Physical Chemistry, RWTH Aachen University, Aachen, Germany.
authors.forename: Halima
authors.initials: H
authors.lastname: Mouhib
authors.affiliation: Yunusov Institute of the Chemistry of Plant Substances, Academy of Sciences of Uzbekistan, Uzbekistan.
authors.forename: Nasir
authors.initials: N
authors.lastname: Mukhamedov
authors.affiliation: Institute of Inorganic Chemistry, RWTH Aachen University, Aachen, Germany.
authors.forename: Ulli
authors.initials: U
authors.lastname: Englert
mesh_terms: D019342:Acetic Acid / Q000737:chemistry*; D001583:Benzoxazoles / Q000737:chemistry*; D001686:Biological Phenomena; D004583:Electrons; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D011789:Quantum Theory; D014961:X-Ray Diffraction
chemical_list: C000611790:(2-oxo-1,3-benzoxazol-3(2H)-yl)acetic acid; D001583:Benzoxazoles; D019342:Acetic Acid
keywords: conformational degrees of freedom; experimental electron density; intermolecular interactions and polarization; multipole refinement; potential energy surface