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The Nature of the Hydrogen Bond: Outline of a Comprehensive Hydrogen Bond Theory.
By Gastone Gilli and Paola Gilli (University of Ferrara, Italy).
Oxford University Press: New York. 2009. xii + 318 pp. $130.
ISBN 978-0-19-955896-4.
   I highly recommend this book to anyone who is truly interested in the hydrogen bond. The title is clearly meant to recall Pauling’s classic book, The Nature of the Chemical Bond, in which he summarizes his work on chemical bonding. In the current book, the Gillis (father and daughter) summarize the work they have published with their co-workers on the hydrogen bond. As such, the current work differs from other recent books on hydrogen bonds, such as that by Jeffrey, which I previously reviewed (J. Am. Chem. Soc. 1998, 120, 5604), much as a paper in Accounts of Chemical Research differs from one in Chemical ReViews.
   The book consists of eight chapters. The first, entitled “A century of the hydrogen bond (H-bond),” is a concise, yet critical, introduction and historical review of hydrogen bonding. The Gillis take care to disabuse the reader of many popular fallacies about H-bonds that pervade the literature. For example, Pauling’s suggestion that H-bonds are electrostatic in nature was meant only to apply to weak (not all) H-bonds. The second chapter deals with definitions, generalities, and preliminary classification of H-bonds based upon the work of others.
   The third and longest chapter covers modeling the H-bond using crystallography. Here, the authors’ considerable expertise in crystallography and practical applications of crystallographic databases plays a very important role. They show how careful interpretation of judiciously chosen crystal structures can deepen one’s understanding of H-bonding. Roughly two-thirds of this chapter deals with resonance-assisted H-bonds (RAHBs), a class of H-bonding that the Gillis have studied in great detail. These H-bonds can be quite strong and, therefore, important to structure determination. This chapter includes an extensive analysis of a subclass of RAHBs that occurs in tautomers of β-diketones, such as acetylacetone. It also includes further classification of H-bonds, including charge-assisted hydrogen bonds (CAHBs).
   In the fourth chapter, the authors discuss modeling H-bonds from a thermodynamic perspective. Detailed discussions of the effects of pKa matching upon the strength of H-bonds, particularly in the cases of CAHBs, are presented as ways of predicting H-bond strengths from thermodynamic data. Included is a very useful “pKa slide rule”. This is followed by a short chapter on “empirical laws governing the H-bond”.
   The sixth chapter, “Outline of a novel transition-state H-bond theory (TSHBT),” includes analyses using valence-bond and density functional theory, analyses of the potential surfaces–which generally include double-well potentials–and the application of Marcus theory to these surfaces. The seventh chapter, “The strength of the H-bond: Definitions and thermodynamics,” covers the strength of H-bonds in different phases and in aqueous solution. It includes a detailed discussion of the principle of enthalpy/entropy compensation as applied to the H-bond. Finally, in the last chapter, the Gillis discuss the role of strong H-bonds in nature, e.g., the importance of H-bond cooperativity in biochemistry, crystal packing, and water.
   No book is perfect, including this one. Among the deficiencies are the choice of an erroneous analysis of the gas-phase electron diffraction of acetylacetoneswhich did not take the fraction of the sample that is not in the enol form, resulting in the hydrogen atom involved in H-bonding appearing to be considerably out of the molecular planesinstead of what seems to be a more correct one (see Lowery et al. J. Am. Chem. Soc. 1971, 93, 6399). The following topics are not discussed: (1) trans-H-bond scalar J-coupling among the NMR methods used for studying H-bonds, (2) the zero-point vibration’s effect upon the experimental structures resulting from surfaces with a low energy barrier in a double-well system; (3) the isotopic substitution method of studying double-well potentials, and (4) the effects of H-bonding on vibrational spectra. Because this book is essentially an overview of the authors’ contributions, less space is allotted to those of other groups. However, this should be expected based on analogy to Pauling’s book. Another problem is that color plates of some of the most important figures, including the aforementioned “pKa slide rule,” are inserted as a group after page 180, without any explanation or notation in the Table of Contents.
   This book should be required reading for biochemists, many of whom seem to have only a superficial idea of what the hydrogen bond really is, as well as for anyone who designs or interprets empirical models that need to reproduce systems where H-bonding is important. On the whole, I believe this book to be a valuable contribution to our understanding of H-bonds. The Gillis should be commended for the considerable time and effort that they must have spent on this endeavor.

J. J. Dannenberg, City University of New York-Hunter
College and The Graduate School
2010 American Chemical Society
The Dual Hydrogen Bond Web Site

  Gastone Gilli 2010 2012