Calculations of the molecular interactions in 1,3-dibromo-2,4,6-trimethyl-benzene: which methyl groups are quasi-free rotors in the crystal?

Dibromomesitylene (DBMH) is one of the few molecules in which a methyl group is a quasi-free rotor in the crystal state. Density functional theory calculations - using the Born-Oppenheimer approximation (BOa) - indicate that in isolated DBMH, Me4 and Me6 are highly hindered in a 3-fold potential > 55 meV while Me2 symmetrically located between two Br atoms has a small 6-fold rotation hindering potential: ∼ 8 meV. Inelastic neutron scattering studies have shown that this is also true in the crystal, the Me2 tunneling gap being 390 μeV at 4.

Crystal structure and Hirshfeld surface analysis of 2,6-di-iodo-4-nitro-toluene and 2,4,6-tri-bromo-toluene.

The title compounds, 2,6-di-iodo-4-nitro-toluene (DINT, CHINO) and 2,4,6-tri-bromo-toluene (TBT, CHBr,), are tris-ubstituted toluene mol-ecules. Both mol-ecules are planar, only the H atoms of the methyl group, and the nitro group in DINT, deviate significantly from the plane of the benzene ring. In the crystals of both compounds, mol-ecules stack in columns up the shortest crystallographic axis, .

Crystal structure of 1,1'-[selanediyl-bis(4,1-phenyl-ene)]bis-(2-chloro-ethan-1-one).

In the title mol-ecule, C16H12Cl2O2Se, the C-Se-C angle is 100.05 (14)°, with the dihedral angle between the planes of the benzene rings being 69.92 (17)°.

Anharmonic Computations Meet Experiments (IR, Raman, Neutron Diffraction) for Explaining the Behavior of 1,3,5-Tribromo-2,4,6-trimethylbenzene.

In the present paper we first show the experimental Raman, infrared, and neutron INS spectra of tribromomesitylene (TBM) measured in the range 50-3200 cm(-1) using crystalline powders at 6 or 4 K. Then, the bond lengths and angles determined by neutron diffraction using a TBM single crystal at 14 K are compared to the computed ones at different levels of theory. Anharmonic computations were then performed on the relaxed structure using the VPT2 approach, and for the lowest normal modes, the HRAO model has led to a remarkable agreement for the assignment of the experimental signatures.

Crystal structure of 1,3,5-trimethyl-2,4-di-nitro-benzene.

In the title compound, C9H10N2O4, the planes of the nitro groups subtend dihedral angles of 55.04 (15) and 63.23 (15)° with that of the aromatic ring.

Iodo-durene.

1-iodo-2,3,5,6-tetra-methyl-benzene), C10H13I, crystallizes in the chiral space group P212121. The I atom is displaced by 0.1003 (5) Å from the mean plane of the ten C atoms [maximum deviation = 0.

Bis(4-acetyl-phen-yl) selenide.

In the title compound, C(16)H(14)O(2)Se, the dihedral angle between the benzene rings is 87.08 (11)°. In the crystal, mol-ecules are linked into layers parallel to the bc plane by inter-molecular C-H⋯O hydrogen bonds.

Rotationally disordered phase of 1,3-dibromo-5-iodo-2,4,6-trimethylbenzene at 293 K.

In the crystal state at room temperature, the molecule of dibromoiodomesitylene (1,3-dibromo-5-iodo-2,4,6-trimethylbenzene), C9H9Br2I, is prone to strong disorder, apparently involving only the three halogen sites (occupied identically by 66.7% Br and 33.3% I).

Vibrational spectra of triiodomesitylene: combination of DFT calculations and experimental studies. Effects of the environment.

A study of the internal vibrations of triiodomesitylene (TIM) is presented. It is known from X-rays diffraction at 293 K that the molecule has nearly D(3h) symmetry because of the large delocalization of the methyl protons. By using Raman and infrared spectra recorded at room temperature, a first assignment is done by comparing TIM vibrations with those of 1,3,5-triiodo- and 1,3,5-trimethyl-benzene.

4-dimethylamino-beta-nitrostyrene and 4-dimethylamino-beta-ethyl-beta-nitrostyrene at 100 K.

The structures of 4-dimethylamino-beta-nitrostyrene (DANS), C10H12N2O2, and 4-dimethylamino-beta-ethyl-beta-nitrostyrene (DAENS), C12H16N2O2, have been solved at T=100 K. The structure solution for DANS was complicated by the presence of a static disorder, characterized by a misorientation of 17% of the molecules. The molecule of DANS is almost planar, indicating significant conjugation, with a push-pull effect through the styrene skeleton extending up to the terminal substituents and enhancing the dipole moment.

Reassessment of methyl rotation barriers and conformations by correlated quantum chemistry methods.

Internal rotations of the methyl group in ortho-substituted and 2,6-disubstituted toluenes in their ground state have been investigated by means of various ab initio quantum chemistry methods. Computed barriers at the Hartree-Fock (HF) level using medium sized basis sets agreed reasonably with experimental results in the case of the studied ortho-substituted toluenes. However, this agreement worsens when using very large basis sets.

The low-temperature phase of 1,3-dibromo-2,4,6-trimethylbenzene: a single-crystal neutron diffraction study at 120 and 14 K.

In the low-temperature phase of dibromomesitylene (1,3-dibromo-2,4,6-trimethylbenzene), C(9)H(10)Br(2), the molecule deviates significantly from the C(3h) molecular symmetry encountered in tribromomesitylene (1,3,5-tribromo-2,4,6-trimethylbenzene), even for the endocyclic bond angles. An apparent C(2v) molecular symmetry is observed. The angle between the normal to the molecular plane and the normal to the (100) plane is approximately 20 degrees.