Structure and Packing in Smectic E and Smectic A Phases in the Series of 4‐n‐Alkyloxy‐4′‐alkanoylbiphenyls

Abstract

By means of X-ray investigations the structure of the SE and S,-phases of the title compounds has been studied. The lattice parameters of the orthorhombic S , structure are given. The thickness of the smectic layers is nearly the same in the SE and S, phases and agrees well with the length of the molecules in their most stretched form. That suggests a similar conformation of the alkyl chains in both phases. A model of the packing in the SA phase is discussed which IS based on a dense packing with antiparallel orientation of molecules with a non-symmetrical shape.Mit Hilfe von rontgenographischen Verfahren wurde die Struktur der SE und S , Phasen der genannten Verbindungen untersucht. Die Gitterparameter der orthorhombischen Struktur in der SE Phase werden angegeben. Die Dicke der smektischen Schichten in der SE und S, Phase ist nahezu gleich und stimmt gut mit der Lange der Molekule in ihrer gestreckten Form iiberein. Dieses Ergebnis legt eine ahnliche Konformation der Alkylketten in beiden Phasen nahe. Es wird ein Packungsmodell fur die SA Phase diskutiert, das auf einer dichten Packung antiparallel orientierter Molekiile von nichtsymmetrischer Form basiert.

Molecular packing analysis of the crystal smectic E phase of a benzothieno-benzothiophene derivative by a combined experimental / computational approach

“…The refinement of the unit cell parameters after the phase transition resulted in a monoclinic angle very close to 90°, independent of temperature. An orthorhombic unit cell was concluded, a result which is comparable to other SmE phases [29][30][31].…”

X‐ray studies of the layer thickness in smectic phases

“…This statement arises from calculations performed with the aid of the Cerius 2 program { . We tried to build a crystal cell by minimization of the intermolecular interaction energy with adjusted unit cell parameters and selected P2 1 2 1 2 and Pba2 space groups, according to the suggestions given by Diele et al [11]. A realistic density value and a compensation of the dipole moments within the cell were achieved for Z54 and the P2 1 2 1 2 space group.…”

“…[3,4]). By comparison the variation of the s-parameter and the layer thickness d with temperature has been less studied [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…This suggests an alignment of the molecular long axes with the c-axis of the unit cell. The value of the b-parameter, being independent of temperature, is typical for substances with aromatic cores [10,11] and should correspond to the molecular diameter. If so, the lattice constant a reflects the intermolecular distance in the cell.…”

Ketonization in Calamitic Liquid Crystals

“…X-ray diffraction of liquid crystals is one of useful methods for the study of the structure of their mesophases [147,148]. As in the case of weakly polar alkyl and alkoxy derivatives [149], monolayer formation (d=L 1, where d is the layer spacing, L is the molecular length) and a dimeric density wave (d=L > 1) have been observed for ketones [51,52,56,60,80,88,120].…”