Edward A. Berry wrote:
Dear all,
Is it possible for a Cl atom attached to an aromatic ring to
accept an H-bond from His NE2?
I'm modeling a low-resolution ligand structure and my favorite fit
shows such a bond, but it is possible the ring is flipped and
an OH or -C=O on the other side of the ring actually make the H-bond.
Thanks,
Ed
A number of people expressed the view that this kind of interaction is possible.
Narayanan Ramasubbu provided a reference:
Ramasubbu, N., Parthasarathy, R. and Murray-Rust, P. Angular preferences of intermolecular forces around halogen centers,
Preferred directions of approach of electrophiles and nucleophiles around carbon-halogen bond. J. Am. Chem. Soc., 108, 4308-4314, 1986.
The interaction described is not actually an H-bond, but a direct HOMO-LUMO
orbital
interaction between the halogen and nucleophile, however the distance is
significantly
less than sum of vdw radii, for example about 3.0 A, making it look
like an H-bond. Thus it wouldn't require NE2 nitrogen to be protonated.
Don't know how much this would contribute to binding energy, as compared
to a hydrogen bond.
Thanks, and
Productive new year to all,
Ed
