The induced freezing of drops of supercooled water covered by uncompressed monolayers of the aliphatic alcohols CnH2n+1OH, n=16-31 was investigated. The ice-nucleation temperatures were found to depend on the length of the hydrocarbon chain and the parity of the number of carbon atoms in the chain. A gradual increase of the freezing point from -14 degrees C leveling off to a plateau at -7.5 degrees C from n = 22 onward was observed for the even series. Alcohols with n odd raised the freezing temperature from -11 to -1 degrees C for n=17-31. Fatty acids (C,H2n+1COOH) or alcohols bearing a fluorocarbon chain or a steroidal backbone as the hydrophobic part induced nucleation of ice at much lower temperatures. Powder X-ray diffraction measurements showed that the monolayer C31H63OH induced formation of hexagonal ice with its (001) face parallel to the monolayer surface. Grazing incidence X-ray diffraction (GID) studies of-uncompressed monolayers of CnH2n+1OH with n=16, 20, 23, 30, 31 on water at 5 degrees C revealed two-dimensional (2D) crysalline self assembly and yieldednd yielded their packing arrangements to near atomic resolution.(1) The extent of 2D crystalline order (i.e. coherence length) and the amount of crystalline material were less for monolayers with n=16 and 20 than for monolayers with n=23, 30, 31 according to a GID analysis, the latter,latter property being independently confirmed by FT-IR. The best lattice match to ice was for n=30 and 31, the lattice match to ice being poorer for n=20 and 16, in terms of area per molecule, correlating with their less efficient ice-nucleation behavior. The packing arrangements of the hydrocarbon chains of monolayers C30H61OH and C31H63OH are very similar, but for the orientation of their CH2OH moieties, which are different, resulting in different ice-nucleation behavior. Further evidence for the role played by the orientation of the C-OH group is the ice-nucleating properties of alcohols CH3(CH2)(m)OX(CH2)mOH (X=O, NH). In these systems the freezing point was found to depend on the parity of m but not on n. The 2D crystal structures of two ester-alcohols n=19, m=9, 10 on water were determined by GID and lattice energy calculations.(1) Finally, mixtures of aliphatic alcohols with different chain lengths (by up to four CH2 groups) substantially reduced the ice-nucleation temperature, implying drastic reduction in the lateral order of the 2D nets of alcohol OH groups. On the other hand, up to 50% fluorocarbon alcohol in a mixture with hydrocarbon alcohol did not reduce the freezing temperature of ice, indicating phase separation of crystalline domains.