Crystal Structure and Conformational Behavior of Smectogenic 2-Phenyl-5-(4-n-pentoxyphenyl) Pyrimidine

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Abstract
The crystal structure of the title compound with the formula C6H5–C4N2H,– C6H4–OC5H11 (2-PPePP) has been determined as part of a study of the conformational behavior of mesogenic phenyl pyrimidines. The compound crystallizes in space group PI with four molecules in a unit cell of dimensions a = 10.055(1), b = 9.621(2), c = 19.223(3) Å, α = 91.30(1), β = 103.90(2), γ = 97.60(2)°. The structure has been solved by direct methods and refined to R = 0.074. The 2-PPePP molecules adopt a stretched form. The pentyloxy groups are partly disordered (molecule 1) and contain gauche bonds. The central pyrimidine ring is approximately coplanar with the phenyl rings attached to it in the 2- and 5-positions with interplanar angles of about 8° in both cases. This somewhat unexpected conformational behavior is compared with the results of stereochemical and theoretical considerations. The 2-PPePP molecules are arranged in the crystalline state exactly parallel to each other forming sheets as well as a tilted layer structure.