1 research outputs found
Phase Behavior and Molecular Packing of Octadecyl Phenols and their Methyl Ethers at the Air/Water Interface
Noncovalent
molecular interactions, such as hydrogen bonding and
van der Waals forces, play an important role in self-assembling to
supramolecular structures. To study these forces, we chose monolayers
at the air/water interface to limit the possible arrangements of the
interacting molecules. Furthermore, monolayers provide useful tools
to understand and study interactions between molecules in a controlled
and fundamental way. The phase behavior and molecular packing of the
phenols 1-(4-hydroxyphenyl)-octadecane (<b>5a</b>), 1-(3,4-dihydroxyphenyl)-octadecane
(<b>6</b>), and 1-(2,3,4-trihydroxyphenyl)-octadecane (<b>3</b>) and their methyl ethers in monolayers at the air/water
interface have been examined by π/A isotherms, Brewster angle
microscopy (BAM), grazing incidence X-ray diffraction (GIXD) measurements,
and density functional theory (DFT) calculations. The phenols are
synthesized by Friedel–Crafts acylation of methoxybenzenes,
hydrogenation of the resulting aryl ketones, and cleavage of the aryl
methyl ethers. In the π/<i>A</i> isotherms and in
BAM, the phenols show patches of the solid condensed phase at large
molecular areas and the monolayers collapse at high pressures. Furthermore,
the dimensions of the unit cell obtained by GIXD measurements are
compatible with an arrangement of the phenyl rings that allows one
aryl ring to interact with four adjacent phenyl rings in an edge-to-face
arrangement, which leads to a significant binding energy. The experimental
data are in good agreement with DFT calculations of 2D crystalline
benzene and <i>p</i>-cresol arrangements. The enhanced monolayer
stability of phenol <b>5a</b> can be explained by hydrogen bonds
of the hydroxyl group with water and van der Waals forces between
the alkyl chains and aryl–aryl interactions