Published in Henry Rzepa's Blog

I previously used data mining of crystal structures to explore the directing influence of substituents on aromatic and heteroaromatic rings. Here I explore, quite literally, a different angle to the hydrogen bonding interactions between a benzene ring and OH or NH groups. I start by defining a benzene ring with a centroid.

References

General Biochemistry, Genetics and Molecular BiologyGeneral Medicine

Short N+—H...Ph hydrogen bonds in ammonium tetraphenylborate characterized by neutron diffraction

Published in Acta Crystallographica Section B Structural Science
Authors Thomas Steiner, Sax A. Mason

The crystal structures of ammonium tetraphenylborate, NH4 +·BPh4 −, are determined by neutron diffraction at 20 and 293 K. At both temperatures, all four N—H vectors of the ammonium ion are time-average-oriented at the midpoints of the phenyl rings of neighboring anions. The N—H...Ph distances, H...M 2.067 and N...M 3.023 Å, are exceptionally short (M = aromatic midpoint). Even at 20 K the ammonium ion performs large amplitude motions which allow the N—H vectors to sample the entire face of the aromatic system.