Hydrogen bonds are a key feature of chemical structure and reactivity. Recently there has been much interest in a special class of hydrogen bonds called "strong" or "low-barrier" and characterized by great strength, short distances, a low or vanishing barrier to hydrogen transfer, and distinctive features in the NMR spectrum. Although the energy of an ordinary hydrogen bond is ca 5 kcal mol-1, the strength of these hydrogen bonds may be > or = 10 kcal mol-1. The properties of these hydrogen bonds have been investigated by many experimental techniques, as well as by calculation and by correlations among those properties. Although it has been proposed that strong, short, low-barrier hydrogen bonds are important in enzymatic reactions, it is concluded that the evidence for them in small molecules and in biomolecules is inconclusive.

No abstract

Is a hydrogen bond symmetric (single-well potential) or asymmetric (double-well potential)? The NMR method of isotopic perturbation of equilibrium was used to answer this question for the monoanions of a wide variety of 18O-labeled dicarboxylic acids. The observed 18O-induced isotope shifts, especially at the ipso carbons, demonstrate that these exist as a pair of equilibrating tautomers in both aqueous and organic solvents. This conclusion for organic solvents is opposite a previous one based on similar data. As a further test, primary isotope shifts, which had been diagnostic for a single-well potential, were reinvestigated. The monoanions of 1,2-cyclopentenedicarboxylic, 3,4-furandicarboxylic, and 3,4,5,6-tetrahydrophthalic acids have negative primary isotope shifts and are confirmed as having asymmetric hydrogen bonds. Although hydrogen phthalate has a positive primary isotope shift, it too is judged to have an asymmetric hydrogen bond, according to 18O-induced isotope shifts, which are considered more reliable.

The Journal of Chemical Education announces a call for papers for an upcoming special issue on diversity, equity, inclusion, and respect in chemistry education research and practice.

Current reforms in content area education present new challenges for literacy educators. These reforms promote engaging students in the practices of the disciplines—teaching students how to participate in an activity in which disciplinary content is produced. Content area literacy (CAL) instruction that supports only the learning of general academic or school literacies undermines these content area reforms and their focus on participation because it does not teach the literacies that students need to participate in the disciplines. In this article, the authors present an argument for why CAL instruction should focus on teaching disciplinary literacies instead of a general academic literacy. The authors show how CAL instruction focused on disciplinary literacies can support the educational goals of both literacy educators and content area reformers. The authors also contrast four corresponding characteristics of both types of CAL instruction and illustrate these with examples.