Molecular conformation and methyl proton delocalization in triiodomesitylene: A combined density functional theory and single-crystal neutron diffraction study

Abstract

Articles you may be interested inStructural optimization of molecular clusters with density functional theory combined with basin hopping Conformational distribution of a ferroelectric liquid crystal revealed using fingerprint vibrational spectroscopy and the density functional theory Structure and conformation properties of 1-alkyl-3-methylimidazolium halide ionic liquids: A density-functional theory study Investigation of structure of liquid 2,2,2 trifluoroethanol: Neutron diffraction, molecular dynamics, and ab initio quantum chemical study First the conformations of various ortho and di-ortho substituted toluenes calculated by quantum chemistry methods are discussed as well as the hindering potentials deduced from the latter results and those established experimentally by microwaves and fluorescence techniques. It appears that methyl ͑Me͒ groups are much less hindered in di-ortho than in ortho substituted compounds. Then the study of the 1,3,5-triiodo-2,4,6-trimethylbenzene ͑triiodomesitylene or TIM͒ is reported. Density functional theory ͑DFT͒ calculations indicate that two conformations of the TIM molecule have the same formation energies. One has C 3h symmetry, the other with the C s symmetry is obtained from the C 3h by a rotation of 60°for one Me. Experimentally, the TIM structure has been determined at 15 K using single-crystal neutron diffraction data. TIM crystallizes in the triclinic space group P Ϫ1. Molecules are stacked in an antiferroelectric manner along the oblique a axis. For two Me groups the experimental conformation is close to the C s one, but the third Me group has a C-H bond nearly orthogonal to the ring plane. Such conformation is unstable in the gas state, but it is stabilized in the crystal by intermolecular interactions, nevertheless DFT predicts accurate bond lengths and angles when the Me conformations are constrained to the experimental ones. The three Me groups, having different environments, experience different hindering potentials, this explains why they are tunnelling at different energies as found by inelastic neutron scattering ͑INS͒. Using INS results, we deduced the potentials hindering the Me groups rotation in the crystal. The proton probability densities ͑PPD͒ calculated from these potentials are in concordance with the crystallographic results. Hence the quantum origin of the broad spreading of PPD observed at 15 K is established. Moreover, it is demonstrated that the crystal field is responsible for the larger part of the potentials hindering the Me groups in the solid state.

CF3 Rotation in 3-(Trifluoromethyl)phenanthrene. X-ray Diffraction and ab Initio Electronic Structure Calculations

“…10 This model is capable of accurately locating hydrogen atoms, yielding results in good agreement with those from neutron diffraction. 11 Relaxed potential energy surfaces (PES) for rotation around the C3-CF3 axis in the isolated molecule were obtained at the HF/6-311+G**//HF/6-31G* level. Energy calculations on the isolated molecule in the ground and rotational transition states, used to compute barrier heights, were done using the HF/ 6-311+G**//HF/6-31G*, 12 B3LYP/6-31G*//B3LYP/6-31G*, B3LYP/6-311+G**//B3LYP/6-311+G** and MP2/6-31G*// MP2/6-31G* 13 theoretical models.…”

Rotational tunneling of methyl groups in low temperature phases of mesitylene: potentials and structural implications

“…In all halo compounds the threefold symmetry of the isolated molecule is lost in the solid states. [5][6][7] This leads to inequivalency of the three methyl groups of a molecule with according specific potentials and tunneling splittings. These materials could and have been prepared as single crystals and are studied in this form by high resolution neutron spectroscopy.…”

Competing stacking modes in crystals of trihalogeno-trimethyl-benzene: Theory meets experiment

“…Our group, in the period 1995-2002, has established that below room temperature, TXM compounds crystallize in the P-1 triclinic group without any apparent disorder and not in the monoclinic group like the others HSB. The structure of the trichloro-mesitylene (TCM) at 150 and 297 K was solved by XRD [12], that of the tribromomesitylene (TBM) was solved at 295 K by XRD [13] and at 14 K by neutron diffraction (ND) [14] while that of the triiodo-mesitylene (TIM) was solved at 293 K by XRD [15] and at 15 K by ND [16].…”