Differentiation of chemically functional groups in stearoyl amide and anilide with scanning tunneling microscopy

Scanning tunneling microscopy (STM) was applied to distinguish chemically functional groups in stearoyl amide and anilide molecules adsorbed on the liquid-solid interface of phenyloctane and graphite. In contrast to previously reported carboxyl and hydroxyl groups, amide and anilide groups were imaged as more readily tunneling parts than the hydrocarbon part. Stearoyl amide molecules were in a head-to-head alignment suggesting hydrogen bonding between the amide groups, while stearoyl anilide molecules were in a head-to-tail arrangement. The STM images were compared with the shape of the molecular orbitals calculated for isolated molecules to confirm the intuitive assignment of the functional groups.