¹³C Detected Scalar Nitrogen−Nitrogen Couplings Across the Intramolecular Symmetric NHN Hydrogen Bond of Proton Sponge

A review with comprehensive data on experimental indirect scalar NMR spin–spin coupling constants across hydrogen bonds

“…Using the perchlorate of 65 [ 15 N 2 ]-labeled, the following couplings were measured for the first time [84] : 1 J NH = 1h J NH = −30.4 Hz and 2h J NN = +8.7 Hz (in 64 2h J NN = 0 Hz).…”

Symmetrization of Cationic Hydrogen Bridges of Protonated Sponges Induced by Solvent and Counteranion Interactions as Revealed by NMR Spectroscopy

“…The values observed were even smaller than those of neutral DAN 7. [50] As the values of JA C H T U N G T R E N N U N G (N,N) are much less influenced by the tautomerism, we undertook the present study in continuation of our previous work [39] on 5 H + of scalar couplings in the systems listed in Scheme 3. For that purpose, we synthesized the doubly 15 N-labeled isotopologues.…”

“…[39] Prior to this, protonated sponges of the DMANH + type were studied mainly by a combination of various experimental and theoretical methods and had focused on the question of whether or not the proton moves in a single or double well. [40][41][42][43] In solution, such information was obtained by studying the effects of isotopic substitution on NMR spectroscopic chemical shifts.…”

The Largest 15N–15N Coupling Constant Across an NHN Hydrogen Bond

“…Whereas the maximum values have been established for FHF and NHF hydrogen bonds, the corresponding maxima are still unknown in the case of NHN bridges. To date, only 2 J15 N 15 N values less than 11 Hz have been detected in nucleic acid base pairs, [3] protonated sponges, [6,7] and six- [8] and seven-membered [9] Hchelates. In contrast, DFT calculations gave maximum coupling constants 2 J NN = 25 Hz, [5d] corresponding to the shortest possible N···N distance of about 2.5 .…”

“…One of these is why the values of J NN of the DPQ anions are much larger than those of the related proton sponges. [6,7] Possible explanations are the differences in the overall charge of the systems, the hybridization of the nitrogen atoms, and the specific nature of the intermolecular interactions. Although further study is required, we do not think charge effects are dominant, as the chemical shifts of the hydrogen-bonded protons in both types of compounds are similar.…”