The preparation of two p-tert-butylcalix[5]arene esters and a p-tert-butylcalix [5]arene carboxylic acid are reported. The cone conformation in solution at 20 "C has been established for all three compounds by 'H NMR spectroscopy. Crystals of pentaethyl ester 2 were studied by X-ray diffraction and the molecule was found t o possess a distorted cone conformation in the solid state. Crystals of 2 are triclinic, space group P i , with two molecules in a cell of dimensions a = 11.656(2), b = 14.91 2(3). c = 23.044(5) A; a = 79.23(2), / 3 = 78.31 (2). y = 67.52(2)". The structure was solved by direct methods and refined by least squares t o R = 0.084 for 6967 reflections. One phenolic ring (B) is tilted inwards at the upper rim of the cone; the others are tilted outwards, but by varying amounts. The pendant side-chains also adopt very different conformations, resulting in a range of inter-chain 0 0 distances around the cavity, from * Details of the deposition scheme are available in 'Instructions for Authors', J. Chem. Soc., Perkin Trans. 2, 1993, issue 1.
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