An X-ray Study of Cyanophenyl Pyrimidines. Part I-Crystal Structure of PCCPP

Abstract

The crystal and molecular structures of the nematogen 5-(trans-4-ethylcyclohexyl)-2-(4-cyanophenyl)-pyrimidine have been determined by direct methods. The crystal belongs to the monoclinic system with space group P2/a, a = 18.437, b = 7.1027, c = 15.342 ° β = 106.07° and Z = 4. Least squares refinement leads to R = 0.049 (R_w = 0.048) for 2246 observed reflections. The molecules are in an almost fully extended conformation. Phenyl and pyrimidine rings are highly planar and lie almost in the ac plane. The cyclohexane ring is in chair form. Pairs of molecules related by a centre of symmetry are packed into sheets in the ac plane and these sheets are stacked along the b-axis. The structure is of a common type for a nematogen and the transition to the mesophase is a simple displacive type. The pairing of molecules resulting from the interaction between opposed dipoles of cyano-groups exists in both the crystalline and the nematic state.

Key Words:

• X-ray study of a nematogen
• crystal structure of a cyanopyrimidine