How strong is a π-facial hydrogen bond?

Abstract
Functional group substitutions (chemical mutations) in a molecular zipper complex have been used to construct a thermodynamic cycle for estimating the strength of a π-facial H-bond between an NH group and an aromatic ring resulting in a lower limit of –4.5 ± 0.5 kJ mol–1 for the magnitude of the intermolecular NH-π interaction in chloroform.