Conformational analysis of MBBA fluorinated analogues by 1H and 13C - NMR

Pivovarova, N. S.; Boldeskul, I. E.; Shelyagenko, S.V.; Fialkov, Yu. A.

doi:10.1016/0022-2860(88)80174-1

Cited by 4 publications

(1 citation statement)

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“…4 These studies have revealed that the aromatic rings are not on the plane of the linking unit because of the internal rotation about the C 2 -C 3 or C 9 -N bonds. Our interests in the present study are focused on the following points: (1) how dihedrals, φ 1 and φ 2 , differ in the crystal, liquid-crystal, and gas phases; (2) the effect of terminal substituents on the φ 1 and φ 2 and the geometry of the core: the electronic properties of the substituents may have an effect on the dihedral angles of φ 1 and φ 2 ; [5][6][7][8] and (3) the configuration of terminal substituents with respective to the core. It is impossible to determine all the principal structural parameters and vibrational amplitudes of MBBA by GED alone.…”

Section: Introductionmentioning

confidence: 99%

Gas-Phase Molecular Structure of MBBA (4-Methoxybenzylidene-4‘-n-butylaniline), a Mesogen, by Electron Diffraction Combined with ab Initio Calculations

et al. 1999

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The molecular structure of a typical mesogen, 4-methoxybenzylidene-4′-n-butylaniline (MBBA, CH 3 O-C 6 H 4 -CHdN-C 6 H 4 -(CH 2 ) 3 -CH 3 ), has been studied by gas-phase electron diffraction (GED). The nozzle temperature was about 150°C. Structural constraints in the GED data analysis were obtained by the ab initio MO calculation at the HF/4-21G(*) level of theory. Vibrational amplitudes and shrinkage corrections were calculated from the harmonic force constants given by a normal coordinate analysis. The phenylene ring attached to the C(dN) atom and the azomethine group (-CHdN-) are essentially on the same plane, i.e., the dihedral angle is 0(12)°. The phenylene ring bonded to the nitrogen atom is found to be out of the plane of the azomethine group and the determined value of the dihedral angle, 48(9)°, in the gas phase is larger than that in the crystalline state. This is mainly due to the steric interaction between the hydrogen atoms of the azomethine group and the phenylene ring. In the gas phase the four rotational conformers with respect to the configurations of the n-butyl group were assumed to exist. Their conformational abundance was fixed, as calculated from the ab initio relative energies. The principal bond distances and angles (r g /Å and ∠ R /deg) determined by GED are r(NdC) ) 1.290 (12), r(C-N) ) 1.413 (12), r(C az -C ring ) ) 1.467 (3), 〈r(C ring -C ring )〉 ) 1.400 (6), ∠C-NdC ) 119.0(18), ∠NdC-C ) 121.6(13), ∠NC ring C 14 ) 128.5(25), ∠C az C ring C 4 ) 121.2 (dependent), 〈CCC ring 〉 ) 120.0(3), 〈∠CCC butyl 〉 ) 116.2(11), ∠C 5 C ring O )129.3 (16), where C az , C ring , and C butyl denote the carbon atoms of the azomethine, phenylene and butyl groups, respectively. C 14 and C 4 are the C atoms of the rings synclinal to the C(dN) atom and cis to the H az atom, and C 5 is the C atom of the ring cis to the C atom of the methoxy group. The values in parentheses are three times the standard deviations. The notation 〈 〉 represents the average value. The transition temperature from the nematic to liquid phases was discussed on the basis of the determined molecular structure.

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Section: Introductionmentioning

confidence: 99%