Structure of CF: A Gas-Phase Electron Diffraction and Quantum Chemical Computational Study of a Remarkably Distorted Fluorofullerene.

The equilibrium molecular structure of the gaseous fluorofullerene CF has been determined for the first time by the electron diffraction method with the use of quantum chemical calculations up to the RI-MP2/def2-TZVPP level of theory. Vibrational amplitudes and quadratic and cubic force constants were calculated by density functional theory methods. It was found that the sample under study consists of the isomer of symmetry, 81(4)%, with a small amount of the isomer of symmetry, in good accordance with HPLC-MS (atmospheric pressure photoionization), HPLC-UV/vis, and NMR spectroscopic data.

Molecular Structure of Pyrazinamide: A Critical Assessment of Modern Gas Electron Diffraction Data from Three Laboratories.

Accuracy and precision of molecular parameters determined by modern gas electron diffraction have been investigated. Diffraction patterns of gaseous pyrazinamide have been measured independently in three laboratories, in Bielefeld (Germany), Ivanovo (Russia), and Moscow (Russia). All data sets have been analyzed in equal manner using a highly controlled background elimination procedure and flexible restraints in molecular structure refinement.

Experiment and theory at the convergence limit: accurate equilibrium structure of picolinic acid by gas-phase electron diffraction and coupled-cluster computations.

The accurate molecular structure of picolinic acid has been determined from experimental data and computed at the coupled cluster level of theory. Only one conformer with the O[double bond, length as m-dash]C-C-N and H-O-C[double bond, length as m-dash]O fragments in antiperiplanar (ap) positions, ap-ap, has been detected under conditions of the gas-phase electron diffraction (GED) experiment (Tnozzle = 375(3) K). The semiexperimental equilibrium structure, rsee, of this conformer has been derived from the GED data taking into account the anharmonic vibrational effects estimated from the ab initio force field.

Nitroxoline Molecule: Planar or Not? A Story of Battle between π-π Conjugation and Interatomic Repulsion.

The conformational properties of the nitro group in nitroxoline (8-hydroxy-5-nitroquinoline, NXN) were investigated in the gas phase by means of gas electron diffraction (GED) and quantum chemical calculations, and also with solid-state analysis performed using terahertz time-domain spectroscopy (THz-TDS). The results of the GED refinement show that in the equilibrium structure the NO group is twisted by angle ϕ = 8 ± 3° with respect to the 8-hydroxyoquinoline plane. This is the result of interatomic repulsion of oxygen in the NO group from the closest hydrogen, which overcomes the energy gain from the π-π conjugation of the nitro group and aromatic system of 8-hydroxyoquinoline.

Molecular structure of clonidine: gas-phase electron diffraction, single-crystal X-ray diffraction and quantum chemical studies.

This study presents the first determination of the molecular structure of the antihypertensive drug clonidine in the gas phase using gas electron diffraction (GED). The refinement was supported by quantum chemical calculations (QCs). The tautomeric and conformational distribution was investigated theoretically, providing an explanation for the presence of the single conformer in the gas phase.

Gas phase equilibrium structure of histamine.

The first gas electron diffraction (GED) experiment for histamine was carried out. The equilibrium structure of histamine in the gas phase was determined on the basis of the data obtained. The refinement was also supported by the rotational constants obtained in previous studies [B.

Conformational and Bonding Properties of 3,3-Dimethyl- and 6,6-Dimethyl-1,5-diazabicyclo[3.1.0]hexane: A Case Study Employing the Monte Carlo Method in Gas Electron Diffraction.

Gas-phase structures of two isomers of dimethyl-substituted 1,5-diazabicyclo[3.1.0]hexanes, namely, 3,3-dimethyl- and 6,6-dimethyl-1,5-diazabicyclo[3.

From the determination of the accurate equilibrium structure of 1-methylthymine by gas electron diffraction and coupled cluster computations to the observation of methylation and flexibility effects in pyrimidine nucleobases.

1-Methylthymine is of particular interest because it can be considered as a simple model of thymidine, in which deoxyribose attaches to thymine precisely at the N1 atom. The structure of this molecule is still unknown and so far has been experimentally studied for the first time in this work. The semiexperimental equilibrium structural parameters (r(e)(se)/∠(e)(se)) of 1-methylthymine have been determined by the gas electron diffraction (GED) method, taking into account vibrational corrections calculated with the use of the anharmonic (cubic) MP2/cc-pVTZ force constants.

Interplay of experiment and theory: determination of an accurate equilibrium structure of 1-methyluracil by the gas electron diffraction method and coupled-cluster computations.

As far as fundamental knowledge is concerned, the methyl derivatives of uracil can be considered as the simplest objects for studying the structural effects due to the substitution in the pyrimidyne nucleobases. From this point of view, 1-methyluracil is of special importance in biochemistry because uracil attaches ribose in ribonucleic acid (RNA) just precisely at the N1 atom. The semi-experimental equilibrium structure (r(e)(se)) of 1-methyluracil has been determined for the first time by the gas electron diffraction (GED) method taking into account rovibrational corrections to the thermal-average internuclear distances calculated with harmonic and anharmonic (cubic) MP2/cc-pVTZ force constants with consideration of the methyl torsion as a large-amplitude motion.

Structure and bonding nature of the strained Lewis acid 3-methyl-1-boraadamantane: a case study employing a new data-analysis procedure in gas electron diffraction.

Base-free 3-methyl-1-boraadamantane was synthesized by starting from its known THF adduct, transforming it to a butylate-complex with n-butyllithium, cleaving the cage with acetyl chloride to give 3-n-butyl-5-methyl-7-methylene-3-borabicyclo[3.3.1]nonane and closing the cage again by reacting the latter with dicyclohexylborane.

Molecular structure of 9H-adenine tautomer: gas-phase electron diffraction and quantum-chemical studies.

Molecular geometry of 9H-adenine tautomer was calculated by MP2 method using several basis sets (up to cc-pVQZ). According to the results of all quantum-chemical calculations, the molecule has an essentially planar heavy-atom skeleton and a quasi-planar amino group. Since the bond lengths of adenine are of similar magnitude, the structural problem could not be solved by the gas-phase electron diffraction (GED) method alone.

Study of the thymine molecule: equilibrium structure from joint analysis of gas-phase electron diffraction and microwave data and assignment of vibrational spectra using results of ab initio calculations.

Thymine is one of the nucleobases which forms the nucleic acid (NA) base pair with adenine in DNA. The study of molecular structure and dynamics of nucleobases can help to understand and explain some processes in biological systems and therefore it is of interest. Because the scattered intensities on the C, N, and O atoms as well as some bond lengths in thymine are close to each other the structural problem cannot been solved by the gas phase electron diffraction (GED) method alone.

Molecular structure of 1,5-diazabicyclo[3.1.0]hexane as determined by gas electron diffraction and quantum-chemical calculations.

The equilibrium molecular structure and conformation of 1,5-diazabicyclo[3.1.0]hexane (DABH) has been studied by the gas-phase electron-diffraction method at 20 degrees C and quantum-chemical calculations.

Molecular structure and conformational composition of 1,3-dihydroxyacetone studied by combined analysis of gas-phase electron diffraction data, rotational constants, and results of theoretical calculations. Ideal gas thermodynamic properties of 1,3-dihydroxyacetone.

The molecular structure of 1,3-dihydroxyacetone (DHA) has been studied by gas-phase electron diffraction (GED), combined analysis of GED and microwave (MW) data, ab initio, and density functional theory calculations. The equilibrium re structure of DHA was determined by a joint analysis of the GED data and rotational constants taken from the literature. The anharmonic vibrational corrections to the internuclear distances (re-ra) and to the rotational constants (B(i)e-B(i)0) needed for the estimation of the re structure were calculated from the B3LYP/cc-pVTZ cubic force field.