Abstract
The size limit of substituents allowing O-through-the-annulus rotation of substituted calix[4]arenes was further extended to the propargyloxy group in 24-propargyloxy-25,26,27-tris(N,N-dimethylcarbamoylmethoxy)-p-tert-butylcalix[4]arene by demonstrating its free but slow motion affording equilibrium between the partial cone and 1,2-alternate conformers. The effect of solvent and upper rim substituents R1 on the conformational inversion was investigated by means of 1H NMR. The rotational isomerisation of the parent (R1 = H) analogue could not unambiguously be detected. The experimental results were supported by comprehensive density functional theory studies.
Acknowledgements
The authors are grateful to K. Tarcsay-Petrov and M. Bojtár for fruitful discussions and suggestions during the preparation of the manuscript.
Notes
1. Present affiliation: XiMo Hungary Ltd., Pusztaszeri út 59-67, Budapest 1025, Hungary.