Posts Tagged ‘energy decreases’

Are close H…H contacts bonds? The dénouement!

Monday, October 10th, 2011

I wrote earlier about the strangely close contact between two hydrogen atoms in cis-butene. The topology of the electron density showed characteristics of a bond, but is it a consensual union? The two hydrogens approach closer than their van der Waals radii would suggest is normal, so something is happening, but that something need not be what chemists might choose to call a “bond“. An NCI (non-covalent analysis) hinted that any stability due to the electron topologic characteristics of a bond (the BCP) might be more than offset by the repulsive nature of the adjacent ring critical point (RCP). Here I offer an alternative explanation for why the two hydrogens approach so closely.