Table 1. Hydrogen Bond Acceptor Strengths (pK_BHX Scale) and Frequencies Observed in the CSD for Selected Hydrogen Bonds Types.

	typical acceptor strength (pKBHX)	frequency of hydrogen bond to OH [%]
Acyclic Oxygen Acceptors
amide	2.2−2.6	48
ketone	1.1−1.2	39
sulfone	1.1	37
sulfonamide	1.0	30
ether	1.0−1.2	16
Planar Heterocycles
N-alkylated imidazole N	2.72	41
pyridine N	1.86	32
oxazole N	1.67	30
pyrazine N	0.92	25
furane O	−0.4	0.5