In the title mol-ecule, C(18)H(17)FN(2), the imidazole ring is essentially planar [maximum deviation of 0.005 (1) Å and makes dihedral angles of 72.33 (8) and 18.71 (8)° with the methyl-phenyl and fluoro-phenyl rings, respectively. The dihedral angle between the two benzene rings is 75.05 (7)°. The crystal packing is stabilized by inter-molecular C-H⋯N hydrogen bonds.

In the title compound, C(18)H(18)N(2), the imidazole ring is essentially planar [maximum deviation = 0.004 (1) Å] and makes dihedral angles of 68.91 (8) and 20.43 (9)° with the tolyl and phenyl rings, respectively. The dihedral angle between the latter rings is 73.62 (8)°. The crystal packing is stabilized by inter-molecular C-H⋯N hydrogen bonds.

In the title mol-ecule, C(27)H(19)FN(2), the imidazole ring is essentially planar [maximum deviation = 0.004 (1) Å] and makes dihedral angles of 62.80 (6), 36.98 (6), 33.16 (6) and 46.24 (6)°, respectively, with the substituent rings in the 1-, 2-, 4- and 5-positions. No classical hydrogen bonds are observed in the crystal structure.

The syntheses and crystal structure of 3-chloro-3-methyl-r-2,c-6-diphenylpiperidin-4-one, C₁₈H₁₈ClNO, (I), 3-chloro-3-methyl-r-2,c-6-di-p-tolylpiperidin-4-one, C₂₀H₂₂ClNO, (II), and 3-chloro-3-methyl-r-2,c-6-bis(4-chlorophenyl)piperidin-4-one, C₁₈H₁₆Cl₃NO, (III), are described. In each structure, the piperidine ring adopts a chair conformation and dihedral angles between the mean planes of the phenyl rings are 58.4 (2), 73.5 (5) and 78.6 (2)° in (I), (II) and (III), respectively. In the crystals, molecules are linked intoC(6) chains by weak N—H...O hydrogen bonds and C—H...π interactions are also observed.

In the title compound, C(17)H(16)N(2)·H(2)O, the imidazole ring is essentially planar [maximum deviation = 0.0037 (7) Å]. The imidazole ring makes dihedral angles of 80.74 (7) and 41.62 (7)° with the phenyl rings attached to the N and C atoms, respectively. The dihedral angle between the two phenyl rings is 75.83 (8)°. Inter-molecular O-H⋯N and O-H⋯O hydrogen bonds are found in the crystal structure.