Paradigms and Paradoxes: The Position of the Lone Pair in Amines: A Comparison Between Bader?s AIM Approach and Pure Geometrical Considerations

Alkorta, Ibón; Elguero, José; Elguero, Eric

doi:10.1007/s11224-004-0735-y

Cited by 46 publications

(57 citation statements)

References 7 publications

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“…[27] This assertion is also supported by the optimized d(O 1 · · ·O C ) distance in 1-syn, (see Table 1) which is shorter than the sum of their van der Vaals radii, 2 × 1.52 Å = 3.04 Å. [28] Recently, this type of interaction between two proximate O atoms was studied, [29] using the Bader's [30] atoms in molecules approach, yielding important insight into its nature and suggesting that such interaction yields at least a stabilizing effect. Similar fluorine lone-pairs overlap was studied previously, [29] showing that it constitutes an efficient pathway for transmitting through space the FC interaction of SSCCs.…”

Section: Resultsmentioning

confidence: 77%

“…[28] Recently, this type of interaction between two proximate O atoms was studied, [29] using the Bader's [30] atoms in molecules approach, yielding important insight into its nature and suggesting that such interaction yields at least a stabilizing effect. Similar fluorine lone-pairs overlap was studied previously, [29] showing that it constitutes an efficient pathway for transmitting through space the FC interaction of SSCCs. [31] In the present case, the overlapping lone-pairs belong to atoms with spin-less nuclei and, therefore, a J O -O SSCC cannot be transmitted through space.…”

Section: Resultsmentioning

confidence: 99%

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On the unusual²Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

Pérez¹,

Suardíaz²,

Ortíz³

et al. 2008

Magnetic Reson in Chemistry

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A remarkable difference for (2)J(C(2)-H(f)) coupling constant in syn and anti conformers of 5-X-furan-2-carboxaldehydes (X = CH(3), Ph, NO(2), Br) and a rationalization of this difference are reported. On the basis of the current knowledge of the Fermi-contact term transmission, a rather unusual dual-coupling pathway in the syn conformer is presented. The additional coupling pathway resembles somewhat that of the J(H-H) in homoallylic couplings, which are transmitted by hyperconjugative interactions involving the pi(C=C) electronic system. The homoallylic coupling pathway can be labeled as sigma*(C-H) <-- pi(C=C) --> sigma*(C-H). In the present case, this additional coupling pathway, using an analogous notation, can be labeled as sigma*(C(2)-C(C)) <-- LP(1)(O(1))...LP(2)(O(C)) --> sigma*(C(C)-H(f)) (sigma*(C(2)-C(C))) where O(1) and O(C) stand for the ring and carbonyl O atoms, respectively. This additional coupling pathway is not activated in the anti conformers since both oxygen lone pairs do not overlap.

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Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

On the unusual²Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

Pérez¹,

Suardíaz²,

Ortíz³

et al. 2008

Magnetic Reson in Chemistry

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“…We have transformed the absolute shields (σ , ppm) into chemical shifts (δ, ppm) using the following equations: δ 1 H = 31.0 − 0.97 σ 1 H; δ 13 C = 175.7 − 0.963 σ 13 C; δ 15 N = −154 − 0.98 σ 15 N; δ 19 F = 128.6 − 0.84 σ 19 F. [14,15,20] At the same level of calculation, the absolute shieldings of the references are: 31 Table 6. Calculated coupling constants (Hz); in the case of nitrogen they correspond to 15 The experimental chemical shifts are reasonably well reproduced except δNH d (δNH c ) ( Tables 1 and 5) because the experimental value includes the effect of intermolecular HBs).…”

Section: Chemical Shiftsmentioning

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

Magnetic Reson in Chemistry

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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.

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“…Such an angular dependence of through-space J(F,F) couplings has recently also been supported by theoretical calculations. [8][9][10][11][12][13] Scheme 2. Compounds studied earlier with regard to through-space F,F coupling.…”

Section: Introductionmentioning

confidence: 99%

Spin–Spin Interactions Across the “Cove” in the (Z) and (E) Isomers of 1,1′‐Difluoro‐9,9′‐bifluorenylidene

et al. 2005

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In the (Z) isomer, but not in the (E) isomer of title compound 1, moderate 19F,19F spin–spin coupling across the “cove” is observed [J(F,F) = 11.0 Hz], which is deemed to obey a through‐space mechanism. The coupling between the isochronous fluorine nuclei of 1Z causes second‐order effects in the 1H, 13C and 19F NMR spectra of this compound and allows its easy distinction from the (E) isomer. A B3LYP/6‐31+G(d) calculation of 1Z as an isolated molecule was carried out which gave a non‐bonded F,F distance d(F,F) of 2.711 Å and an angle between the two C–F bond vectors of 34.1°. The computed F···F compliance constant of 6.96 Å/mdyn points to a very weak interaction. According to our previous correlation between d(F,F) and through‐space J(F,F), the F,F distance in 1Z would be expected to go along with a coupling constant of ca. 46 Hz. This discrepancy between prediction and experiment gives support to our earlier presumption that a simple d(F,F)/J(F,F) correlation may not sufficiently describe through‐space couplings and that an angular factor should also be taken into account. An X‐ray diffraction study of 1Z resulted in an F,F distance of 2.638 Å and an angle between the C–F bonds of 36.4°, in fair agreement with the MO calculation. The rigidity of the (Z) isomer was studied using theoretical compliance constants. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Paradigms and Paradoxes: The Position of the Lone Pair in Amines: A Comparison Between Bader?s AIM Approach and Pure Geometrical Considerations

Abstract: The position of the lone pair of 17 amines has been located with the help of Bader's AIM methodology. This position has been compared with those estimated with simple geometrical models. It appears that these models are convenient only for some symmetrical or undistorted cases.

Cited by 46 publications

References 7 publications

On the unusual²Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

On the unusual²Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

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

Spin–Spin Interactions Across the “Cove” in the (Z) and (E) Isomers of 1,1′‐Difluoro‐9,9′‐bifluorenylidene

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Paradigms and Paradoxes: The Position of the Lone Pair in Amines: A Comparison Between Bader?s AIM Approach and Pure Geometrical Considerations

Abstract: The position of the lone pair of 17 amines has been located with the help of Bader's AIM methodology. This position has been compared with those estimated with simple geometrical models. It appears that these models are convenient only for some symmetrical or undistorted cases.

Cited by 46 publications

References 7 publications

On the unusual2Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

On the unusual2Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

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

Spin–Spin Interactions Across the “Cove” in the (Z) and (E) Isomers of 1,1′‐Difluoro‐9,9′‐bifluorenylidene

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On the unusual²Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes

On the unusual²Jcoupling dependence onsyn/antiCHO conformation in 5‐X‐furan‐2‐carboxaldehydes