Syntheses and crystal structures of 2-(p-tolyl)-1H-perimidine hemihydrate and 1-methyl-2-(p-tolyl)-1H-perimidine

The title compounds, 2-(4-methylphenyl)-1H-perimidine hemihydrate (1, C18H14N2 center dot-0.5H(2)O) and 1-methyl-2-(4-methylphenyl)-1H-perimidine (2, C19H16N2), were prepared and characterized by H-1 NMR and single-crystal X-ray diffraction. The organic molecule of the hemihydrate lies on a twofold rotation axis while the water molecule lies on the intersection of three twofold rotation axes (point group symmetry 222). As a consequence, the hydrogen atoms that are part of the N-H group and the water molecule as well as the CH3 group of the p-tolyl ring are disordered over two positions. In compound 1, the perimidine and the 2-aryl rings are slightly twisted while its N-methylated derivative 2 has a more distorted conformation because of the steric repulsion between the N-methyl group and the 2-aryl ring. In the crystal structures, molecules of perimidine 2 are held together only by C -H center dot center dot center dot pi contacts while the parent perimidine 1 does not exhibit this type of interaction. Its crystal packing is established by inter-molecular N -H center dot center dot center dot O hydrogen bonds with the solvent water molecules and additionally stabilized by pi-pi stacking.