Hydrogen-bonded order in mercury-supported monolayers of end-functionalized alkanes

The order formed by hydrogen bonding in mercury-supported Langmuir films (LFs) of end-functionalized, surface-parallel, alkane molecules was studied by surface-specific X-ray methods and surface tensiometry. Hexadecane derivatives, substituted at one or both ends by mercapto, carboxy, or hydroxy moieties were studied. The dimensionality of the monolayer's surface-parallel order was found to correspond to the number of molecular carboxyl groups, with the zero-, one-, or two-carboxyl molecules exhibiting no, one-, or two-dimensional order, respectively. The observed structural motifs are rationalized based on the molecular conformations and bonding synthons. Similarities, or otherwise, with the corresponding structure of three-dimensional (3D) crystals and graphite-supported LFs are also discussed.