Crystal structure of 3,4-diphenyl-N-cyclohexylpyrrole-2,5-dione.

component for functional dyes because it contains two electronwithdrawing and one electron-donating groups. Studies to understand how substituents to the 1H-pyrrole-2,5-dione skeleton influence its structure and properties are of particular interest from the viewpoint of the development of novel functional dyes. We determined the structure of 1,3,4triphenyl-pyrrole-2,5-dione (Fig. 1(I))1 and demonstrated that the three phenyl rings significantly influence the structure of the 1H-pyrrole-2,5-dione skeleton. To evaluate any effect caused by replacing the phenyl group at the N atom by the cyclohexyl group, we undertook an X-ray analysis of the title compound (Fig.1(II)). A yellow prismatic crystal with dimensions of 0.4 × 0.3 × 0.3 mm was obtained from an acetone solution at 293(1)K and used for diffraction experiments. The crystal and experimental data are given in Table 1. The structure was solved by direct methods and refined by full-matrix least-squares methods with anisotropic temperature factors for non-H atoms. All H atoms were found from difference Fourier maps, and were refined with isotropic temperature factors. The atomic parameters for nonhydrogen atoms are listed in Table 2. Selected bond distances and angles are listed in Table 3. An ORTEP III4 drawing of the title compound together with the atomic and ring numberings is shown in Fig. 2. The pyrroline ring is essentially planar, and ring II adopts a normal chair conformation. The dihedral angles between the least-squares plane of ring I and those of rings II, III and IV are 87.8(1), 39.8(1), and 35.8(1) ̊, respectively. The corresponding dihedral angles relevant to rings III and IV in compound (I) are 44.7(1) and 32.2(1) ̊, respectively. The bond distances and angles within the phenyl rings are within the expected ranges. The N1–C2 and N1–C5 bond lengths are significantly shorter than the corresponding values in (I). On the other hand, the N1–C1a, C2–C3 and C4–C5 bond lengths are significantly longer than the values in (I). The exocyclic bond angles around the N1–C1a bond are more asymmetric than those in (I). These geometrical changes indicate that replacing the phenyl group by the cyclohexyl group at the N1 position brings about a significant effect on the structure of the 1H-pyrrole-2,5-dione skeleton. There is an intramolecular C–H···O hydrogen bond between the C2a and O2 atoms [C2a···O2 3.233(4), C2a–H 1.13(4), H···O2 2.45(4)Å, C2a–H···O2 126(3) ̊], which is depicted as the dotted line in Fig. 2. The asymmetry of the exocyclic bond angles around the N1–C1a bond may be partly due to this intramolecular hydrogen bond. Although the molecules are mainly linked by van der Waals forces in the crystal, there are 1473 ANALYTICAL SCIENCES DECEMBER 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry