Molecular Structure ofp-Azoxyanisole, a Mesogen, Determined by Gas-Phase Electron Diffraction Augmented by ab Initio Calculations

Abstract

As the first attempt to determine the gas-phase structure of molecules forming liquid crystals, the molecular structure of p-azoxyanisole (PAA, CH 3 O-C 6 H 4 -NOdN-C 6 H 4 -OCH 3 ), a mesogen, has been studied by gas electron diffraction. A high-temperature nozzle was used to vaporize the sample. The temperature of the nozzle was about 170°C. Structural constraints were taken from HF/4-21G(*) ab initio molecular orbital calculations on PAA. Vibrational amplitudes and shrinkage corrections were calculated from the harmonic force constants given by normal coordinate analysis. The structural model assuming four conformers well reproduced the experimental data. Five bond distances, six bond angles, and two dihedral angles were determined. Mean amplitudes were adjusted in five groups. The dihedral angles between the phenylene rings and the azoxy plane have been determined to be 11(26)°and 11(11)°, and these values are in agreement with those in the solid phase determined by X-ray diffraction within experimental errors. The conformation of the core of this mesogen is mainly ascribed to the interaction between the π-electrons of the azoxy group and the aromatic rings.

Structural determination of vanillin, isovanillin and ethylvanillin by means of gas electron diffraction and theoretical calculations

“…Therefore, the samples were heated by using the nozzle reported in Ref. [8]. The acceleration voltage of incident electrons was about 37 kV and the electron wavelength was calibrated to the r a (C=S) distance of CS 2 (1.5570 Å) [9].…”

Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations

“…The vapor pressure of caffeine is not high enough for the electron diffraction experiment at room temperature and the sample was heated to 185 ˚C by using the nozzle system reported in Ref. [12]. The acceleration voltage of incident electrons was about 38 kV and the electron wavelength calibrated to the r a (C=S) distance of CS 2 (1.5570 Å) [13] was 0.06327 Å.…”

Influence of liquid crystalline ordering on the properties of selected cured nematic epoxy materials

“…The number of diffraction maxima visible in the plot of I(s) for product 2 is 9, which suggests that the paracrystalline phase may have relatively complex structure in this case. The triple character of the pattern near 1.9 nm −1 and 2.7 nm −1 may be related not only to presence of the second component (amine) in the mixture, but also to molecular structure of AU1 compound itself, which may exist in more than one conformation-according to ab initio calculations (Kuze et al, 1998).…”