2,6-Dimethylylbenzoic acid–2,6-dimethylylpyridine-18-crown-5

Abstract

C20H23NO6, M r = 373.4, orthorhombic, Pbca, Z = 8; at room temperature: a = 8.843 (2), b = 20.558 (4), c = 19.783 (6) A, U = 3596.4 A 3, D x = 1.379 g cm-3; at --160°C: a = 8.752(3), b -- 20.498 (6), c = 19.664 (5) A, U = 3527.7 /~3, Dx = 1.406 g cm -a. The least-squares refinement converged at R(F) = 0.062 for 1822 (low-temperature) obser- vations. The molecule has approximate C 2 symmetry, and its overall conformation is determined by polar intramolecular interactions. The transannularly located carboxylic acid and pyridine substituents link via an O-H...N hydrogen bond (2.66 A), thus effectively filling the space within the macrocyclic ring. Introduction. The title compound is one of several crown ether species which we have studied in order to examine the conformational features of various macro- cyclic polyether ligands, and to assist in the inter- pretation of their binding properties. An earlier paper reported the structure of 2,6-dimethylylbenzoic acid- 18-crown-5 (Goldberg, 1976; referred to hereafter as BACR5), and showed that the molecular conformation in the solid is uniquely stabilized by internal hydrogen bonding which involves the convergent carboxylic acid group. We report here the structural results for a similar macrocyclic moiety that also contains one 2,6-dimethylylpyridine unit as part of the 18- membered ring. Chemical information on both com- pounds has recently been published (Newcomb, Timko, Walba & Cram, 1977; Newcomb, Moore & Cram, 1977). /-N