Structural study of the 1-3-5 trifluorobenzene dimer stability: from liquid to gas densities using supercritical conditions (original) (raw)
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Evidence of dimer formation in neat liquid 1,3,5-trifluorobenzene
Chemical Physics Letters, 1996
1,3,5-Trifluorobenzene neat liquid has been studied in comparison with benzene and perfluorinated benzene using neutron diffraction experiments and molecular dynamics simulation. These investigations reveal that the short-range local order is markedly different in 1,3,5-trifluorobenzene liquid, and involves 'dimers', in which the molecules have a parallel stacked configuration, and an average intermolecular distance of less than 4 ,~.
The Journal of Physical Chemistry B, 1998
The local structure in benzene-1,3,5-trifluorobenzene (BT), hexafluorobenzene-1,3,5-trifluorobenzene (HT), and benzene-hexafluorobenzene (BH) equimolar mixtures has been investigated by neutron diffraction experiment and molecular dynamics (MD) simulation. Experimentally it is found that the local order is very slightly affected in the temperature range investigated (298-346 K). The comparison between the present experimental data and those deduced from the assumption of ideality in using structure data on pure components revealed a variety of behaviors for the three mixtures investigated. When small differences are observed for the BT and FT mixtures, more significant deviations appear for the BH mixture. In this context, MD simulations indicate that in BT and FT mixtures each component tends to preserve its local structure (i.e., the one existing in the corresponding pure liquid), while between unlike molecules, C 6 H 6 (or C 6 F 6) and 1,3,5-C 6 H 3 F 3 , the local structure appears as governed by the 1,3,5-C 6 H 3 F 3 molecules. In contrast, for the BH mixture a strong structural enhancement upon mixing occurs: well defined heterodimers, in a quasistacked configuration (intermolecular distance ∼3.7 Å), are found. These heterodimers are also responsible of orientational correlations at larger distances (in the intermediate range, about 7-11 Å). Finally, the role of the competition between repulsive, dispersive, and electrostatic forces in the above mixtures is discussed in detail.
The structure of fluid trifluoromethane and methylfluoride
Journal of Physics: Condensed Matter, 2000
We present hard X-ray and neutron diffraction measurements on the polar fluorocarbons HCF 3 and H 3 CF under supercritical conditions and for a range of molecular densities spanning about a factor of ten. The Levesque-Weiss-Reatto inversion scheme has been used to deduce the site-site potentials underlying the measured partial pair distribution functions. The orientational correlations between adjacent fluorocarbon molecules -which are characterized by quite large dipole moments but no tendency to form hydrogen bonds -are small compared to a highly polar system like fluid hydrogen chloride. In fact, the orientational correlations in HCF 3 and H 3 CF are found to be nearly as small as those of fluid CF 4 , a fluorocarbon with no dipole moment.
Journal of Molecular Liquids, 2010
The development of new effective intermolecular potential models of benzene and hexafluororbenzene, capable in reproducing the thermodynamic and structural properties of molecular systems in a wide range of thermodynamic state points has been presented and discussed. Subsequently, the properties of the fluids have been investigated by employing molecular dynamics and Monte Carlo simulation techniques. The main purpose of this study was to reveal information concerning the liquid state, vapor-liquid equilibrium and supercritical phase properties of these fluids. In the case of the supercritical phase, we mainly focused on the behavior of local density inhomogeneities and related properties. Our calculations reveal that the local density augmentation is much more pronounced in the case of hexafluorobenzene. The origins of possible resemblances and discrepancies with available experimental data have been also systematically discussed and related to our conclusions reported in previous publications. The local density reorganization dynamics as a function of the bulk density and the size of the local region have been also studied, revealing a significant density and length scale dependence similar to the ones presented for other pure supercritical fluids in previous publication of our group.
Physical Review B, 2011
We report on the interplay between the short-range order of molecules in the liquid phase of 1,1,2,2-tetrachloro-1,2-difluoroethane and the possible molecular conformations, trans and gauche. Two complementary approaches have been used to get a comprehensive picture: analysis of neutron-diffraction data by a Bayesian fit algorithm and a molecular dynamics simulation. The results of both show that the population of trans and gauche conformers in the liquid state can only correspond to the gauche conformer being more stable than the trans conformer. Distinct conformer geometries induce distinct molecular short-range orders around them, suggesting that a deep intra-and intermolecular interaction coupling is energetically favoring one of the conformers by reducing the total molecular free energy.
The high-temperature phase of 1,2,4,5-tetrafluoro-3,6-diiodobenzene and the phase transition
Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry
The crystal structure of the high-temperature phase (II) of the title compound, C6F412, has been determined by single-crystal X-ray diffraction. The crystal was grown in a thin capillary tube and then supercooled to room temperature. The space group P2~/c is the same as in the lower-temperature phase (I). The unit cell is a = 8.026 (4), b = 6.069 (4), c = 9.239 (4)/k and fl = 100.27 (5) ° , which has 2.4% more volume than that of phase (I). The structure was solved and refined using a constrained-refinement technique, where an R factor of 5.4% was reached on refinement with 813 structure factors. No significant molecular distortion from the free molecular geometry of mmm, and no appreciable internal vibrations of the molecule could be detected. The low-temperature phase is characterized by an increase in the intermolecular distances involving the iodine atoms, and the phase transition involves relative movement in which one molecule moves 3.7 A in its plane with very little reorientation.
Gas phase structure of trifluoromethyliminosulfurdifluoride, CF3NSF2, revisited
Journal of Molecular Structure, 2000
The gas phase structure of trifluoromethyliminosulfurdifluoride, CF 3 NySF 2 , was reinvestigated by a joint analysis of gas electron diffraction (GED) and microwave spectroscopy. Quantum chemical calculations were performed with the HF, MP2 and B3LYP methods using 6-31G ء basis sets. The GED intensities and MW rotational constants B and C were fitted best with a syn configuration (CF 3 group syn with respect to SF 2 ) and staggered orientation of the CF 3 group with large amplitude torsional motion around the C-N bond. The following skeletal geometric parameters (r g distances and r a angles with 2s uncertainties) were derived: SyN Њ. The values for the SyN and N-C distances and for the F-S-F angle differ appreciably from those derived in an earlier GED investigation. The HF approximation reproduces all bond lengths to within^0.02 Å and the MP2 and B3LYP calculations predict the SyN and the S-F bonds to be longer. The bond angles are reproduced very well with all three methods. ᭧
Chemical Physics Letters, 2003
The torsional potential of trifluoromethoxybenzene around the aryl-O bond was investigated with the aid of largescale ab initio calculations performed at the Møller-Plesset second order (MP2) level, with several post-MP2 methods, and with a hybrid density functional method (B3LYP). Contrary to several recent reports, we do not find substantial qualitative differences between MP2 and B3LYP results, provided sufficiently large basis sets are used. The results are confronted with analogous MP2 and B3LYP data for methoxybenzene, for hypothetical anions as obtained by deprotonation at the para-position, and for ethylbenzene. The trends in the calculated torsional potentials, barrier heights and energy differences between conformers are discussed and correlated with selected structural parameters.
Journal of Molecular Structure, 2001
Tri¯uoromethoxybenzene (TFMB) can occur in a conformation with the OCF 3 group in the plane of the phenylgroup ([e]form) and with the OCF 3 group perpendicular to the phenyl plane ([o]-form). Ab initio calculations on the MP2/6-31G pp level give the [o]-form as the energy minimum with the [e]-form as the top of the rotation barrier about 1.4 kcal/mol above the [o]minimum. In contrast, DFT calculations on the B3LYP/cc-pvtz level give the [e]-and [o]-forms as energy minima with a small (,0.3 kcal/mol) energy difference and a small (,0.5 kcal/mol) barrier between them. Extensive vibrational spectroscopic studies (IR and Raman) of the gaseous, the liquid and the solid (glass and crystal) state gave evidence of TFMB occurring in the gas phase, and in the liquid and amorphous solid as a mixture of [o]-and [e]-forms. In the crystal (annealed at 155 K) the [o]form dominates. Electron diffraction intensities of the gas, ®tted to a dynamic model, resulted for room temperature in the ratio [o]/[e] 70%/ 30%, i.e. the [o]-form being 0.4 kcal/mol more stable than the [e]-form with a barrier of 2.8 kcal/mol between them. q