Determination of the “Privileged Structure” of 8‐Hydroxyquinoline

Abstract

An accurate semi-experimental equilibrium structure of 8hydroxyquinoline (8-HQ) has been determined combining experiment and theory. The cm-wave rotational spectrum of 8-HQ was recorded in a pulsed supersonic jet using broadband dual-path reflection and narrowband Fabry-Perot-type resonator Fourier-transform microwave spectrometers. Accurate rotational and quartic centrifugal distortion constants and 14 N quadrupole coupling constants are determined. Rotational constants of all 13 C, 18 O and 15 N singly substituted isotopologues in natural abundance and those of a chemically synthesized OD isotopologue were used to obtain geometric parameters for all the heavy atoms and the hydroxyl hydrogen from a number of structure determination models. Theoretical approaches allowed for the determination of a semi-experimental equilibrium structure, r SE e in which computed rovibrational and electronic corrections were utilized to convert vibrational ground state constants into equilibrium constants. Despite the molecule having only a horizontal plane of symmetry and possessing 11 individual heavy atoms, microwave spectroscopy has allowed for a reliable and accurate structure determination. A mass dependent, r 2 ð Þ m structure was determined and proved to be equally reliable by comparison with the B3LYP-D3(BJ)/aVTZ equilibrium structure.

Accurate Biomolecular Structures by the Nano-LEGO Approach: Pick the Bricks and Build Your Geometry

“…In addition, as the presence of condensed cycles may impose some strains on the geometry, resulting in a loss of accuracy for the structural parameters describing the neighborhoods of the contact points of the rings, the theoretical values of the C9−C10 distance and the C4C10C9, C5C10C9, C3C4C10, and C6C5C10 angles have been used as predicate observations. The resulting SE equilibrium geometry, reported in Table 4, is in fair agreement with the mass-dependent r m (2) geometry of McNaughton et al, 81 with the difference that in the present case, 21 structural parameters have been directly refined instead of 6.…”

“…For the purpose, the determination of the equilibrium geometry of 8-hydroxyquinoline (8-HQ) and benzofuran, whose structures and atom labeling are detailed in Figure , has been considered. For the former, a SE equilibrium geometry has been recently obtained based on the measurement of the rotational constants for 13 isotopologues (namely, all singly 13 C isotopic substitutions, the 15 N and 18 O ones, and the deuteration of the OH group) . However, due to the lack of C–D-containing isotopologues, the mass-dependent structural evaluation model has been adopted and a number of constraints have been imposed in the fit, with C–H distances and CCH angles fixed to B2PLYP-D3/aug-cc-pVTZ values.…”

“…Following the nano-LEGO procedure, the theoretical equilibrium structure of 8-HQ has been obtained by exploiting the TMA using phenol and pyridine as templates. This has been used as a guess geometry in the SE least-squares fitting procedure based on the experimental rotational constants as well as the B3LYP-D3 vibrational and electronic corrections reported in ref . During the fits, all the structural parameters have been relaxed, with the exception of CH and HCC bond lengths that have been kept fixed at the TMA theoretical values.…”

“… a Bond lengths in Å and angles in °. Figures in parentheses are standard deviations in the units of the last significant digits. b This work. c From ref . …”