A Chiral “Frozen” Hydrogen Bonding in C4-Symmetric Inherently Chiral Resorcin[4]arenes: NMR, X-ray, Circular Dichroism, and Theoretical Study (Eur. J. Org. Chem. 18/2008)
The cover picture shows the X-ray structure of CC4-symmetric, chiral resorcinarene substituted with L-leucine at the upper rim. The molecule is held in the inherently chiral conformation (resembling a chiral CC4-symmetric propeller) by means of twelve intramolecular hydrogen bonds. The seams of hydrogen bonds can be directed in one particular direction because of diastereomeric preferences. The determination of the direction of the hydrogen-bonding seam and the correlation with CD spectra is discussed in the article by A. Szumna et al. on p. 3069 ff.