Correlating Solution‐ and Solid‐State Structures of Conformationally Flexible Resorcinarenes: Significance of a Sulfonyl Group in Intramolecular Self‐Inclusion

The synthesis of tetramethoxyresorcinarene podands bearing p‐toluene arms connected by ‐SO(3)‐ (1) and ‐CH(2)O‐ (2) linkers is presented herein. In the solid state, the resorcinarene podand 1 forms an intramolecular self‐inclusion complex with the pendant p‐toluene group of a podand arm, whereas the resorcinarene podand 2 does not show self‐inclusion. The conformations of the flexible resorcinarene podands in solution were investigated by variable‐temperature experiments using 1D and 2D NMR spectroscopic techniques as well as by computational methods, including a conformational search and subsequent DFT optimisation of representative structures. The (1)H NMR spectra of 1 and 2 at room temperature show a single set of proton signals that are in agreement with C (4v) symmetry. At low temperatures, the molecules exist as a mixture of boat conformations featuring slow exchange on the NMR timescale. Energy barriers (ΔG (≠) (298)) of 55.5 and 52.0 kJ mol(−1) were calculated for the boat‐to‐boat exchange of 1 and 2, respectively. The results of the ROESY experiments performed at 193 K and computational modelling suggest that in solution the resorcinarene podand 1 adopts a similar conformation to that present in its crystal structure, whereas podand 2 populates a more versatile range of conformations in solution.