The effect of fluorination (2): dependence of alkyl chain length on the crystal structures of mesogenic alkyl 4-[2-(perfluorohexyl)ethoxy]benzoates

Abstract

The crystal structures of a series of alkyl 4-[2-(perfluorohexyl) ethoxy] benzoates have been studied, with varying numbers of carbon atoms, n, in the alkyl chain. When n = 1 the perfluoroalkyl and alkyl chains were found to aggregate separately from one other, but when n = 5, 6 or 9 the chains aggregated alternately. An intermediate type, of separate and alternate types of packing, was observed when n = 4. Powder X-ray diffraction results strongly suggested that when n = 12 the alternate type of packing was again present, even though the length of the alkyl chain was then twice that of the perfluoro chain; when n = 9 this ratio was 1.5. These features are similar to those observed previously for the octyl analogues, with the exception of the member of the octyl series in which n = 11 and the ratio of alkyl to perfluoro chains was 1.4, for which the separate type of packing was observed. It is concluded that in the hexyl series the alternate type of packing gives sufficient stabilisation of the members with longer chains.

Keywords:

• perfluoroalkyl chain
• crystal structure
• smectic A
• fluorophobic effect

Acknowledgements

We are grateful to Professors Hitoshi Kawaji and Tooru Atake of the Tokyo Institute of Technology for the powder XRD measurements.

Notes

Note: An earlier article in this series has been published as in Reference [8].