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2] Rotananes were first prepared by solid-phase synthesis (I. T. Harrison. S. Harrison. J. Am. C h m . Soc. 1967, 89. 5723-5724) and by directed synthesis (G. Schill. H Zollenkopf, Liehigs Ann. Clium 1969. 721. 53-74). For an early use o f the hydrophobic effect to direct rotaxane synthesis see H. Ogino. J Am. Chmi. Soc. 1981Soc. , 103, 1303Soc. -1304. For some recent rotaxanes see: a) D. B.

Combined crystallographic and IR spectroscopic study of the hydrogen bond network in the synthetic sex steroid mestranol indicates that a C•C-H ... O hydrogen bond can be considerably enhanced if the C•C-H donor simultaneously accepts an O-H ...

In the crystal structuores of three terminal alkynes, long GC-H * G42 contacts with H C separations in the range 2.7-3.1 A are observed. Despite the long distances, these contacts possess the characteristic infrared spectroscopic features of weak hydrogen bonds. This provides direct evidence that the range of C-H A interactions donated by sufficiently acidic C-H groups extends beyond van der Waals separation. In two of the crystal structures, the C-H --4 R interactions form interconnected systems C S -H CZEZE-H * CEEEE-H.

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