Control of functional group proximity and direction by conformational networks: synthesis and stereodynamics of persubstituted arenes

The cooperative nonbonded interactions present in hexaethylbenzene result i n an arrangement of alkyl groups such that the 1,3,5 and 2,4,6 substituents point to opposite faces of the benzene ring. Correspondingly, derivatives of hexaethylbenzene have their functional groups convergent (meta as in 1,3 ,5-trisubstituted-2,4,6-triethylbenzene) or divergent (ortho, para as in 1, 2-disubstitnted-3,4,5,6-tetraethylbenzenes or 1,4-disubstituted-2,3,5,6-tet raethylbenzenes) due to this cooperative conformational network. To illustr ate this structural feature and probe its dynamics, 1,4-di-X-2,3,5,6-tetrae thylbenzenes have been synthesized. The dynamic stereochemistry of the disu bstituted compounds has been studied by variable temperature H-1 NMR spectr oscopy. Using the same strategy, the 1,3,5-tris(CH2Y)-2,3,6-triethylbenzene s have also been prepared. The steric bulk of the substituent in the disubs tituted compounds has been found to influence the barrier height. The trend s found are applicable for the use of these compounds as angular building b locks for the design of ligands, polymers, and supramolecular architectures . (C) 2001 Elsevier Science Ltd. All rights reserved.