N-Chloroacetyl-3,5-dimethyl-2,6-diphenylpiperidin-4-one(CADMPO), C21H22Cl NO2, FW = 355.85, monoclinic, P2(1), a = 8.2082(10)Angstrom, b = 10.4889(10)Angstrom, c = 10.6175(10)Angstrom, beta = 91.833(10)degrees, V = 913.73(17)Angstrom(3), Z = 2, D-calc = 1.293 Mg/m(3), mu = 1.953 mm(-1), F-000 = 376, CuKalpha = 1.5418Angstrom, final R1 and wR2 are 0.0399 and 0.0911, respectively N-Chloroacetyl-3-ethyl-2,6-diphenylpiperidin-4-one (CAEPO), C21H22ClNO2, F.W = 355.85, monoclinic, P2(1)/n, a = 10.3626(6)Angstrom, b = 8.5702(5)Angstrom, c = 21.6930(10)Angstrom, beta = 92.25(1)degrees, V = 1925.06(18)Angstrom(3), Z = 8, D-calc =1.228 Mg/m(3), mu = 0.211 mm(-1), F-000 =752, MoKalpha = 0.71073Angstrom, final R1 and wR2 are 0.0623 and 0.1397, respectively. Crystal structure studies of these two 4-piperidones show that the piperidones adopt twist-boat conformation. The C-H ... O type of intermolecular interactions play a role in stabilizing the molecules in the unit cell in addition to van der Waals forces.