Figure 10. Molecules with hydrogen bond donor (D-H) and acceptor (A) functionalities in proximity often occur in a thermodynamic equilibrium between closed (left) and open (right) conformations

From

It Is Important to Compute Intramolecular Hydrogen Bonding in Drug Design?

María J. R. Yunta

American Journal of Modeling and Optimization. 2017, 5(1), 24-57 doi:10.12691/ajmo-5-1-3