Spectroscopic and structural evidence for the hydrogen bond nature of CC---H…C=C contacts in ethynyl steroids |
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Authors: | Bert Lutz Jan A Kanters John van der Maas Jan Kroon Thomas Steiner |
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Abstract: | Structural and IR-spectroscopic evidence is given that directed contacts from terminal alkynes to C=C double bonds possess the essential characteristics of weak hydrogen bonds. The contacts are directed at the center of the π-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 Å, with the shortest distances being 2.5 Å. The interaction is of pronounced long-range nature and can be detected in the infrared spectrum even with a long H…π distance of almost 3.0 Å. The sample used is mainly composed of ethynyl steroids belonging to the progestine family. |
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