What is a hydrogen bond? Mutually consistent theoretical and experimental criteria for characterizing H-bonding interactions
The maturity of a science can be measured in terms of successively improved operational definitions of its terms of reference. From this perspective, the science of hydrogen bonding remains in a somewhat immature and unsettled state, reflecting current uncertainties in empirical diagnosis, theoretical origin, and formal definition of this important phenomenon. Authentic progress in the H-bonding sciences should therefore be accompanied by efforts to formulate improved quantitative criteria for identifying, characterizing, and delimiting the H-bonding phenomenon, consistent with best current understanding. The present paper proposes such criteria in a form that better summarizes current understanding of H-bonding and allows progressive refinements of its definition as improved theoretical and experimental methods become available.