N-Dodecylaldonamide monolayers are representative two-dimensional systems for the study of chiral discrimination effects of diastereomers. Enantiomeric and racemic monolayers of N-dodecylmannonamide are investigated at the air-water interface using Brewster angle microscopy, surface pressure-area isotherms, and constant surface pressure relaxation measurements. The striking differences in the pi-A isotherms demonstrate homochiral discrimination with preferred interaction between the same enantiomers. The condensed phase domains of the enantiomers are feather-like dendrites with anisotropically grown side arms, which are chirality-dependent clockwise or counterclockwise curved. The growth patterns of the racemic monolayers evolve similar side arms, but curved in both directions. This indicates spontaneous chiral seggregation. The chiral properties of the N-dodecylmannonamide monolayers are completely different than those of the heterochiral N-dodecylgluconamide monolayers. These chiral differences are correlated to the sugar head group conformations which are known from X-ray diffraction and/or cross polarization magic angle spinning C-13-NMR spectroscopy.