ISSN:
1435-1536
Keywords:
Key words X-ray diffraction
;
Polymorphism
;
Diol derivatives
;
Liquid crystals
;
Hydrogen-bridged network
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The different phases occurring in homologous dried n-alkane-1,2-diols (1,2-diols) and n-alkane-1,2,1′,2′-tetraols (1,2-boladiols), as well as in hydrated n-alkane-1,2-diols were characterised according to their X-ray diffraction patterns. The analysis of the X-ray data is mainly based on the small-angle region. The scattering in the wide-angle region, which may be regarded as fingerprint, is at present used for a qualitative discrimination of the phases. A homologous series of compounds is considered isostructural if the data show a linear relationship between the repeat distance d L and the number of C atoms (Cm) in a chain. Assuming that a given lateral packing remains constant, two characteristic values can be obtained from the plot of d L versus Cm. The slope b contains information about the tilt angle of the chains for the respective layer model and the intercept a represents the thickness of the hydrophilic part of the aggregate. A great variety of headgroup thicknesses and tiltings of the chains were found. Bilayers or double bilayers are the repeat unit in 1,2-diols, whereas in 1,2-boladiols the molecules are packed in monolayers. Water changes the packing of the chains and new packing modes with crossed chain axes were obtained. The ability to form hydrogen-bridged networks on both ends of the molecules forces the chains to occupy larger areas in dried 1,2-boladiols compared to the corresponding 1,2-diols.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s003960050442
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