As known for its 1.0 version, the iBonD is a user-friendly internet-based databank of heterolytic (pK_a) and homolytic (BDE) bond dissociation energies, established by the bond energy team at Tsinghua University and Nankai University, China. Now, it is upgraded to the 2.0 version. The most noteworthy features of iBonD 2.0 are: 1) 7500 homolytic bond dissociation enthalpy (BDE) values for over 5,000 representative organic compounds with various kinds of chemical bonds are now made readily searchable online, and 2) the pK_a compilation is now substantially enriched to have more than 30,000 experimental equilibrium acidity data for about 20,000 compounds in various solvents. Thus, the iBonD 2.0 provides the heretofore most comprehensive bond energy collection and the most convenient approach to find the data with its powerful searching engine.

Chemistry is basically the science on bond reorganizations through bond-cleavage and -formation that are governed intrinsically by the energy of relevant bonds and externally by reaction conditions. Enormous bond energies such as BDE, pK_a, have been accumulated in past, which played key roles in promoting chemistry to become a rational science. The famous Hammett Equation and Brönsted Equation were developed, in fact, by using pK_as. However, frustration is often encountered in finding the right data from oceans of literature, due to lack of a powerful searching engine. As a consequence, the great value of bond energy as a quantitative guide in doing rational chemistry has been much depressed. Hence, the iBonD is built to untangle such a problem for internet users.

In addition, in iBonD 2.0 we recommended “best value” for most compounds in each solvent to avoid possible vacillation encountered when one chooses a pK_a from multi-sources. The pK_as here embraced are normally well accepted in literature or the latest ones reported by the same group. The gas-phase acidity, defined as ΔG⁰_acid in kcal/mol, is also included. Because gas phase BDE data of most compounds inherently bear much greater uncertainty than pK_a, up to 5 carefully selected BDE values for a single molecule but from different groups are presented for selected compound when applicable, with the starred value being the most recommended. Need to mention is that some pK_as or BDEs were not compiled here, such as “ion-pair pK_as” in weakly polar solvent (e.g. THF) and the pK_as of metal complexes, due to the concerns on their intrinsic accuracy or complexity of structure and nomenclature.

Further updating of iBonD to compile the BDE values in solutions, the BDEs of metallic bonds, the energetics of some weak interactions (e.g. hydrogen bond, coordination bond) etc. will be done in our routine maintenances.

The iBonD is provided free of charge for non-profit making academic use only. The users of the iBonD are requested to cite this website http://ibond.nankai.edu.cn in their publication/ presentation whenever applicable. All rights are reserved by the iBonD team.

Feedbacks from users are highly valuable for improving the iBonD and will be most appreciated.

Contact information: Dr. Jin-Dong Yang: jdyang@mail.tsinghua.edu.cn