Conformational Characteristic of p-tert-Butylcalixarene Ethers

Article abstract of DOI:10.1021/jo00093a019

The conformational characteristics of a variety of O-substituted p-tert-butylcalix<6>arenes have been studied by means of the 1H NMR patterns arising from their ArCH2Ar methylene protons and from the position of the 13C NMR lines arising from the carbons bearing these protons.On the basis of this information, the tribenzyl trimethyl ether 13, the bis-calixarenes 15 and 16, the monobenzyl ether 3, the monobenzyl pentamethyl ether 10, and the hexakis(p-cyanobenzyl) ether 19b are established as having cone conformations at ambient temperature.The tetrabenzyl dimethyl ether 14, the tetrabenzoyl esters 17a-d, the tetraarylmethyl ethers 18a-d, and the bridged ether 21, on the other hand, are found to possess 1,2,3-alternate conformations.The conformational mobilities of these compounds were assessed by variable temperature 1H NMR spectral measurements, leading to the classification of the structures as immobile, semimobile, or mobile with respect to conformational interconversion via the "lower rim through the annulus" pathway.