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Hexa-O-alkylated/?-feri-butylcalix [6] arenes with an alternate 1, 3, 5-Rt-2, 4, 6-R2-substitution pattern have been prepared andstudied by NMR spectroscopy. When Rt= CH3 and R2 is a bulky substituent, the calix [6] arene moiety adopts predominantly a flattened cone conformation. At room temperature this conformation slowly interconverts with a 1, 2, 3-alternate conformation (AG*=

70-88 kJ mol-1, T— 328 K, CDCI3). The Gibbsfree energy between these two conformations at T= 303 K in CDCI3 varies from 2 to 7 kJ mol-1. From quantitativeNOE data (obtained for l, 3, 5-trimethoxy-2, 4, 6-tris [(3-nitrobenzyl) oxy]-p-fert-butylcalix [6] arene (10) three-dimensional structures of the flattened cone and the 1, 2, 3-alternate conformers were calculated. In both conformers the methoxy groups are accommodated in the annulus of the calix [6] arene skeleton, indicating specific interactions with the aromatic calixarene moiety …