B. Lutz et al., SPECTROSCOPIC AND STRUCTURAL EVIDENCE FOR THE HYDROGEN-BOND NATURE OFC-C-H...C=C CONTACTS IN ETHYNYL STEROIDS, Journal of molecular structure, 440(1-3), 1998, pp. 81-87
Structural and IR-spectroscopic evidence is given that directed contac
ts from terminal alkynes to C=C double bonds possess the essential cha
racteristics of weak hydrogen bonds. The contacts are directed at the
center of the a-bond rather than at one of the individual C-atoms. The
contact distances from H to the center of the C=C bond are typically
2.8 Angstrom, with the shortest distances being similar to 2.5 Angstro
m. The interaction is of pronounced long-range nature and can be detec
ted in the infrared spectrum even with a long H...pi distance of almos
t 3.0 Angstrom. The sample used is mainly composed of ethynyl steroids
belonging to the progestine family. (C) 1998 Elsevier Science B.V.