Water-Induced Structural Changes in Crown Ethers from Broadband Rotational Spectroscopy

Abstract

The complexes of 12-crown-4 ether (12C4) with water, generated in a supersonic jet, have been studied using broadband Fourier transform microwave spectroscopy. Three 1:1 and one 1:2 clusters have been observed and their structures unambiguously identified through the observation of isotopologue spectra. The structures of the clusters are based on networks of O-H···O and C-H···O hydrogen bonds. The most abundant 1:1 cluster is formed from the most stable S symmetry conformer of 12C4, even though it is not the energetically favored water complex. Interestingly, the structures of the most stable water cluster and the other remaining observed 1:1 and 1:2 complexes are formed from the second or the fifth most abundant conformers of 12C4. This shows the existence of a mechanism that changes the conformation of 12C4 so that the host-guest interactions can be maximized, even for a "soft" ligand like water.

Medium-sized rings: conformational preferences in cyclooctanone driven by transannular repulsive interactions

“…Structural investigations of larger cyclic ketones will yield information on the balance of intramolecular forces in more flexible and complex rings and help elucidate possible trends as the size of the ring increases. These results can be compared with those from recent rotational studies of large ring crown ethers [51][52][53] , where attractive CH…”

Where's water? The many binding sites of hydantoin

“…28 or the 12-crown-4 ether with 2.779(3) Å. 29 The observed shortening can be attributed to a larger donor character of the -NH group of hydantoin with respect to aliphatic hydrogens as those in the systems mention above. This marked acidity contributes to the strengthening of the stability of the overall hydrogen network, which manifests itself as shorter interaction distances.…”

“…It is observed that both the solvate and the water clusters adjust their structures to achieve optimum binding, such as the complexes involving camphor, 27 b-propiolactone, 28 and the 12-crown-4 ether. 29 If the solvate molecule offers a number of strong binding positions for water, like in the case of hydantoin, it can be envisioned that the situation can be different and that the water molecules bind separately to the solvate. In addition, cooperativity effects might play a role.…”

Structure Determination, Conformational Flexibility, Internal Dynamics, and Chiral Analysis of Pulegone and Its Complex with Water

“…In addition, rotational spectroscopy allows us to characterize intra‐ and intermolecular interactions, as we showed recently for camphor–water and formamide–water clusters . Relevant questions are what are the preferred binding positions of water to the molecule of interest and the responsible interactions, as well as how the structure of the solutes can be affected by (micro)solvation?…”

“…[19] Relevant questions are what are the preferred binding positions of water to the molecule of interesta nd the responsible interactions, as well as how the structure of the solutes can be affected by (micro)solvation? [20] An unambiguous differentiation of the enantiomerso fc hiral molecules in the gas phase is possible with the newly developed microwave three-wavem ixing (M3WM) technique. [21,22] M3WM has been applied to an umber of terpenes and alcohols, including those with several stereogenic centers, [23] as well as for the analysiso fc hiral mixtures.…”