DIOL MONOLAYER STRUCTURE ON THE WATER-SURFACE AND ON SOLID SUBSTRATES

The influence of specific changes to the molecular constitution of an alkane-1,2-diol was investigated by studying four related compounds in monolayer form on the water surface with surface pressure-area isothe rms, on Formvar substrates using transmission electron diffraction, an d on Ag+-exchanged glass substrates using scanning tunneling microscop y. The four compounds were chosen to observe the effects of converting methylene groups into ether linkages and parts of the chain into benz ene rings. While all deposited monolayers showed evidence for local cr ystalline packing, there was a positive correlation between the intens ity of the diffraction peaks and the degree of condensation of the wat er-surface monolayer. One of the compounds displayed an unusual chiral packing, two further substances were packed with a hexagonal unit cel l characteristic of a rotator phase, and a fourth showed a primitive r ectangular unit cell indicative of herringbone alternation of the benz ene ring planes. The molecular arrangement within the unit cell of the herringbone structure is deduced from comparison with related structu res and from dense packing principles. A contradiction between the lat ter two is noted.