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The size limit of substituents allowingO-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 R1on the conformational inversion was investigated by means of1H 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. [ABSTRACT FROM AUTHOR]