Interpretation of vicinal proton–proton coupling constants of heteroaromatic molecules in terms of topological electron density descriptors

Abstract

The indirect vicinal proton-proton coupling constants for pyrrole, furan, thiophene and 15 related heteroaromatic compounds were calculated using the Khon-Sham approximation. An analysis of the four Ramsey contributions to the coupling constants was carried out showing that the Fermi contact term is always positive and dominant, although the remaining contributions have a nonnegligible net negative contribution. The trends observed for the proton-proton coupling constants were rationalized in terms of the properties of the electron density. It was found that electron delocalization between the corresponding hydrogen atoms plays a major role on the observed behavior with the charges of the carbon atoms bonded to them and the accompanying geometric variations being also of importance in the coupling mechanism.

Latin American contributions to quantum chemical topology

“…For example, the proton-proton coupling constants and their 4 Ramsey contributions were computed for heteroaromatic compounds such as pyrrole, furan, thiophene, and other 5-membered ring molecules. [89] It was found that although the contact term is dominant in most cases, there are molecules where the other components are also important, as can be seen in Figure 15. The trends observed for the coupling constants were rationalized in terms of electron density descriptors using multivariate correlations of the form…”

“…This approach has been extended to a wide variety of systems. For example, the proton–proton coupling constants and their 4 Ramsey contributions were computed for heteroaromatic compounds such as pyrrole, furan, thiophene, and other 5‐membered ring molecules . It was found that although the contact term is dominant in most cases, there are molecules where the other components are also important, as can be seen in Figure .…”

Synthesis of Highly Substituted Adamantanones from Bicyclo[3.3.1]nonanes

“…Likewise, reaction of 2 with thiophene 5g in the presence of triflic acid afforded the 2- and 3-substituted products, 4g and 4g ′, in a 1.2:1 ratio in yields of 26 and 21%, respectively. The assignment was made by comparing the coupling constants for the three aromatic protons and by analogy to literature data …”