The terminal alkynes: a versatile model for weak directional interactions in crystals

摘要

Terminal alkynes, C ≡ C-H, are the currently best studied type of C-H hydrogen bond donors, and serve as a model to explore weak hydrogen bond effects in general. This is because of their strong donor and acceptor potentials, and their good suitability for infrared spectroscopic experiments. An overview is given on the hydrogen bond functions of the terminal alkyne residue. It is shown that in crystal structures, terminal alkynes form hydrogen bonds with strong acceptors like O = P as well as with weak acceptors like phenyl rings and C ≡ C and C = C moieties. Geometric data is given for these types of interactions. Terminal alkynes can, furthermore, accept π-type hydrogen bonds from strong and also from weak donors, including such from other alkyne groups. The ability to operate as donor and acceptor simultaneously enables terminal alkynes to participate in cooperative hydrogen bond networks with the same functions as hydroxyl groups. Insights into weak hydrogen bond effects obtained from terminal alkynes serve for a better understanding of the hydrogen bond phenomenon as such.