Neutron Diffraction and Molecular Dynamics Study of Liquid Benzene and Its Fluorinated Derivatives as a Function of Temperature

Abstract

The study of the local translational and orientational ordering in benzene (C6H6), 1,3,5-trifluorobenzene (C6H3F3) and hexafluorobenzene (C6F6) neat liquids has been performed along their liquid−vapor coexistence curve between the melting point and the boiling point combining neutron diffraction experiments and molecular dynamics simulation. Both experiment and simulation show that the local ordering is only very slightly affected in the temperature range investigated. The analysis of the results show that the orientational local order in liquid benzene is almost isotropic at distances corresponding to the first shell of neighbors. In contrast, for hexafluorobenzene, parallel and perpendicular configurations exhibit maxima of occurrence for distinct r values, parallel configurations being predominant at short distances. For 1,3,5-trifluorobenzene, the orientational order in the first shell is strongly anisotropic, and a stacked configuration involving a pair of molecules is observed at short distances (about 4 Å). This finding together with the value of the coordination number obtained from simulation data clearly shows the existence of dimers (sandwichlike). Finally it is argued that the orientational and translational ordering observed in the hexafluorobenzene is intermediate between those of benzene and those of 1,3,5-trifluorobenzene.

Liquid structure of benzene and its derivatives as studied by means of X-ray scattering

“…These different results may arise from the fact that the previous X-ray scattering studies accepted the quasi-lattice structure for the liquid based on the crystal structure of benzene. A slightly favourable presence of the parallel and perpendicular configurations was indicated by the molecular dynamics simulation [10,11]. However, our result suggests that the parallel (stacked) configuration is not the major one and the perpendicular configuration exists predominantly.…”

“…On the other hand, the result by a pulsed neutron total scattering experiment at room temperature supported the T configuration in which two molecules are inclined at about 73 [9]. On the contrary to the above observations, analyses of neutron scattering data from the liquid to the supercritical states with the aid of the molecular dynamics simulation revealed that there is no preferential orientational ordering of the neighbouring molecules on average at ambient conditions although the parallel and perpendicular configurations are slightly favoured [10,11]. Thus, much different results on the structure of liquid benzene have been reported so far.…”

“…Much attention has been paid for its hexagonal molecular structure by many chemists and a lot of investigations have been done. The structural studies for liquid benzene have also been performed by the X-ray [1][2][3][4][5][6][7][8] and neutron scattering methods [6,[9][10][11], and computer simulation [10][11][12]. Narten [5] reported that the liquid structure of benzene at 25 C is similar to that found in the crystalline state.…”

Molecular Dynamics Simulation Studies of Benzene, Toluene, and p-Xylene in a Canonical Ensemble

“…That is why the average C-C-C-H torsional energy is the same as K 3 Structural properties. The radial distribution function, g(r), is defined as (14) where ρ 0 is the bulk density, N(r, ∆r) is the number of molecules in a shell which is between r − ∆r/2 and r + ∆r/2 from the center of a molecule with ∆r = 0.005 nm, V(r, ∆r) is the volume of the shell, and <···> indicates the isothermal-isobaric ensemble (NpT) average. The center of mass g(r) of liquid benzene, toluene, and p-xylene at 283.15, 303.15, 323.15, and 343.15 K are shown in Figures 1-3, respectively, and the site-site g C-C (r) of liquid benzene, toluene, and p- xylene at 283.15 K is also shown in Figure 4.…”

Polarizable Empirical Force Field for Aromatic Compounds Based on the Classical Drude Oscillator

“…The computed values of D s were corrected for system size effects using the hydrodynamic model of Yeh and Hummer 78 of a particle surrounded by a solvent with a viscosity, η, (4) Isothermal compressibilities were calculated from (5) where V is the volume, 〈δV 2 〉 are volume fluctuations and K B is the Boltzmann's constant.…”