The Hydrogen Bond Can Be Described Statistically

1 This problem is illustrated by the statement in a 1973 textbook The one definite fact about hydrogen bonds is that there does not appear to be any definite rules which govern their geometry [385]. 

In the crystal, the descriptor structure has a static conotation, and crystal structure analyses provide precise information on individual three-dimensional architectures. As described in Part I A, Chap. 2.3, hydrogen-bond lengths and angles are soft parameters and in any one crystal structure, a particular bond may be compressed or expanded by up to 20% of its equilibrium bond length (Part IA, Chap. 4.3). 

To obtain significant bond length distributions, two important distinctions must be made  

Hydrogen-Bond Donors and Acceptors Occurring in Biological Molecules 

C-O-H Sugars, amino acid side chains, ribonucleic acid 

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