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

The present study shows that a hydrogen bond between the OH group and the fluorine atom is not involved in the (1h)J(FH) spin-spin coupling transmission either for 4-bromo-2-fluorophenol or 2-fluorophenol. In fact, according to a quantum theory of atoms in molecules analysis, no bond critical point is found between O-H and F moieties. The nature of the transmission mechanism of the Fermi contact term of the (1h)J(FH) spin-spin coupling is studied by analyzing canonical molecular orbitals (see J. Phys. Chem. A 2010, 114, 1044), and it is observed that virtual orbitals play only a quite minor role in its transmission. This is typical of a Fermi contact term transmitted mainly through exchange interactions owing to the overlap of proximate electronic clouds; therefore, it is suggested to identify them as (nTS)J(FH) coupling where n stands for the number of formal bonds separating the coupling nuclei. In the cases studied in this work is n = 4. Results presented in this work could provide an interesting rationalization for different experimental signs known in the current literature for proximate J(FH) couplings.

Section: Resultsmentioning

confidence: 75%

“…[1,2] Recently, Alkorta et al [3] published a review reporting nh J X,Y SSCCs including 1h J FH = À 4.42 Hz in 4-bromo-2-fluorophenol. [4] However, there is some evidence that, at least in some instances, O-H. .…”

Section: Introductionmentioning

confidence: 98%

^1hJ_FHcoupling in 2‐fluorophenol revisited: Is intramolecular hydrogen bond responsible for this long‐range coupling?

Cormanich

Moreira

Freitas

et al. 2011

“…We consider this interpretation unwarranted' [note that never did Rae et al [6] suggested that the intramolecular hydrogen bond (IMHB) was strong]. The second aspect is related to a series of papers by Limbach et al [8,10] concerning the 2h J(F-H· · ·N) couplings (about −97 Hz), which are complementary to those studied here. Note that when the proton is transferred, in the first case a very unstable situation Table 1.…”

Section: Introductionmentioning

confidence: 76%

“…[1,2] Later on, some of us published 'A review with comprehensive data on experimental indirect scalar NMR spin-spin coupling constants across hydrogen bonds' [8] where again [6] was cited but not. [1,2] Two other things are relevant in this context.…”

Section: Introductionmentioning

confidence: 99%

A DFT and AIM analysis of the spin–spin couplings across the hydrogen bond in the 2‐fluorobenzamide and related compounds

Alkorta

Elguero

Limbach

et al. 2009

Self Cite

In 1975 a large number of coupling constants were measured in 2-fluorobenzamide labeled with (15)N. Some of them were assigned to couplings through intramolecular N-H...F hydrogen bonds (HBs). These couplings change dramatically when CDCl(3) is replaced by DMSO-d(6). In this theoretical paper we provide density functional theory (DFT) calculations that justify the existence of a weak HB in the absence of solvent, while solvents that act as HB acceptors break down the intramolecular hydrogen bond (IMHB) of 2-fluorobenzamide. Atoms in molecules (AIM) analyses and Steiner-Limbach plots were used to analyze the structure of the compounds.

“…The tautomeric and exchange processes complicate reliable measurement of the 1 J(N,H) values in many molecules with the hydrogen bonding. [3] Nevertheless, the decrease in the absolute size of the 1 J(N,H) coupling constant by 2-4 Hz in the Z-isomer of 2-(2-acylethenyl)pyrroles (Scheme 1) due to a strong N-H· · ·O intramolecular hydrogen bond was revealed, and this experimental finding was supported by density functional theory (DFT) calculations. [4] However, the increase of the 1 J(N,H) coupling constant by 2-3 Hz was observed in the series of 2-substituted pyrroles with the weak N-H· · ·N(O) intramolecular hydrogen bonds.…”

Section: Introductionmentioning

confidence: 87%

GIAO, DFT, AIM and NBO analysis of the NH···O intramolecular hydrogen‐bond influence on the¹J(N,H) coupling constant in push–pull diaminoenones

Afonin¹,

Ushakov²,

Vashchenko³

et al. 2010

In the series of diaminoenones, large high-frequency shifts of the (1)H NMR of the N-H group in the cis-position relative to the carbonyl group suggests strong N-H...O intramolecular hydrogen bonding comprising a six-membered chelate ring. The N-H...O hydrogen bond causes an increase of the (1)J(N,H) coupling constant by 2-4 Hz and high-frequency shift of the (15)N signal by 9-10 ppm despite of the lengthening of the relevant N-H bond. These experimental trends are substantiated by gauge-independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3-bis(isopropylamino)-1-(aryl)prop-2-en-1-one (12) for conformations with the Z- and E-orientations of the carbonyl group relative to the N-H group. The effects of the N-H...O hydrogen-bond on the NMR parameters are analyzed with the atoms-in-molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the N-H...O hydrogen bond as compared with that of 1,1-di(pyrrol-2-yl)-2-formylethene (13) where N-H...O hydrogen bridge establishes a seven-membered chelate ring, and the corresponding (1)J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) --> sigma*(N-H) hyperconjugative interaction is weakened on going from the six-membered chelate ring to the seven-membered one due to a more bent hydrogen bond in the former case. A dominating effect of the N-H bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the (1)J(N,H) value as a consequence of the N-H...O hydrogen bonding in the studied diaminoenones.