Interpreting 2hJ(F,N), 1hJ(H,N) and 1J(F,H) in the hydrogen‐bonded FH–collidine complex

Ab initio EOM‐CCSD calculations were performed to determine ¹⁹F,¹H, ¹⁹F,¹⁵N and ¹H,¹⁵N spin–spin coupling constants in model complexes FH–NH₃ and FH–pyridine as a function of the F—H and F—N distances. The absolute value of ¹J(F,H) decreases and that of ^1hJ(H,N) increases rapidly along the proton‐transfer coordinate, even in the region of the proton‐shared F—H—N hydrogen bond. In contrast, ^2hJ(F,N) remains essentially constant in this region. These results are consistent with the recently reported experimental NMR spectra of FH–collidine which show that ^1hJ(H,N) increases and ¹J(F,H) decreases, while ^2hJ(F,N) remains constant as the temperature of the solution decreases. They suggest that the FH–collidine complex is stabilized by a proton‐shared hydrogen bond over the range of experimental temperatures investigated, being on the traditional side of quasi‐symmetric at high temperatures, and on the ion‐pair side at low temperatures. Copyright © 2002 John Wiley & Sons, Ltd.     

Through‐space 19F–19F spin–spin coupling in ortho‐fluoro Z‐azobenzene

We report through‐space (TS) ¹⁹F–¹⁹F coupling for ortho‐fluoro‐substituted Z ‐azobenzenes. The magnitude of the TS‐coupling constant (^TSJ_FF) ranged from 2.2–5.9 Hz. Using empirical formulas reported in the literature, these coupling constants correspond to non‐bonded F–F distances (d_FF) of 3.0–3.5 Å. These non‐bonded distances are significantly smaller than those determined by X‐ray crystallography or density functional theory, which argues that simple models of ¹⁹F–¹⁹F TS spin–spin coupling solely based d_FF are not applicable. ¹H, ¹³C and ¹⁹F data are reported for both the E and Z isomers of ten fluorinated azobenzenes. Density functional theory [B3YLP/6‐311++G(d,p)] was used to calculate ¹⁹F chemical shifts, and the calculated values deviated 0.3–10.0 ppm compared with experimental values. Copyright © 2015 John Wiley & Sons, Ltd.     

One-bond 1J(15N─19F) spin–spin coupling constants of cationic fluorinating reagents: Insights from DFT calculations

We have investigated, by means of density functional theory protocols, the one-bond ¹J(¹⁵N─¹⁹F) spin–spin coupling constants in a series of fluorinating reagents, containing the N─F bond, recently studied experimentally. The results of the calculations show a very good linear relationship with the experimental values, even though only the M06-2X(PCM)/pcJ-2//B3LYP/6-311G(d,p) level affords a very low mean absolute error. The calculations allow to analyze the various molecular orbitals contributions to the J coupling and to rationalize the observed positive sign, corresponding to a negative sign of the reduced spin–pin coupling constant K(N─F). Moreover, of the four Ramsey contributions, only the diamagnetic spin orbit is negligible, whereas the paramagnetic spin orbit and spin dipole terms decrease the magnitude of the Fermi contact (FC) term by an amount that goes from a minimum of 35% up to more than 60% of the FC term itself. Several effects have been investigated, namely, the contribution of the long-range solvent reaction field, relativistic corrections, and conformational and vibrational effects.     

Intramolecular and Intermolecular Magnetic Coupling Mechanism of a Dinuclear Copper(II) Complex

Abstract. A new dinuclear complex, [Cu₂(μ_{1, 3}‐NCS)₂(Ophen)₂(OH₂)₂], (HOphen = 1, 10‐phenanthrolin‐2‐ol) was synthesized and its crystal structure was determined by X‐ray crystallography. In the complex, the Cu^II ion assumes a distorted square pyramidal arrangement and the thiocyanate anion functions as bridged ligand and Ophen as capped ligand. The analysis of the crystal structure shows that there exists a π–π stacking interaction between the adjacent complexes. The theoretical calculations reveal that the magnetic coupling pathways from the thiocyanate anions bridge ligand and the π–π stacking magnetic coupling pathway resulted in the weak ferromagnetic interactions with 2J = 18.46 cm^–1 and 2J = 10.46 cm^–1, respectively. The calculations also display that the spin delocalization and the spin polarization occur in the bridge magnetic coupling system and the π–π stacking magnetic coupling system, and the magnetic coupling mechanism of the π–π stacking can be explained with McConnell I spin‐polarization mechanism. The fitting for the data of the variable‐temperature magnetic susceptibility with dinuclear Cu^II formula gave the magnetic coupling constant 2J = 2.84 cm^–1 and zJ′ = 0.03 cm^–1, in which the 2J = 2.84 cm^–1 is attributed to the magnetic coupling from the bridge dinuclear Cu^II unit and the zJ′ = 0.03 cm^–1 is ascribed to the π–π stacking magnetic coupling system. The study may benefit to understand the magnetic coupling mechanism of π–π stacking system.     

19F coupling constants and chemical shifts in some dimethylamino and alkoxy derivatives of tellurium hexafluoride,cis TeF4XY

The spectra of A₂BC spin systems provided by the ¹⁹F nuclei in cis (RO) (MeO)TeF₄ and (RO) (Me₂N)TeF₄ (R = Me, Et, Pr, i-Pr) have been recorded and analysed. The geminal coupling constants ²J(F,F) range from 137–174 Hz and trends in the ¹⁹F chemical shifts permit complete assignment of the resonances. Stereospecific coupling between ¹⁹F and the protons of the N-methylamino groups is also observed.     

The B–N Bond in Some Aminoboranes and an Iminoborane,Studied by 11B and 15N NMR Spectroscopy and DFT Methods

¹⁵N NMR spectra of several aminoboranes (Me₂B–NMe₂, Cl₂B–NMe₂, Br₂B–NMe₂, OCH₂CH₂OB–NMe₂), three N‐pyrrolylboranes, and an iminoborane (tBu–B≡N–tBu) was measured. The spin‐spin coupling constants ¹J(¹⁵N, ¹¹B) were resolved at elevated temperatures. In the case of the iminoborane at 105 °C, the coupling constant ¹J(¹⁴N,¹¹B) = 57 Hz could also be determined from the ¹¹B NMR spectrum [from ¹⁵N NMR ¹J(¹⁵N,¹¹B) = 81 Hz]. Generally, there is no correlation between the magnitude of ¹J(¹⁵N,¹¹B) and the bond length d_BN. The values ¹J(¹⁵N,¹¹B) indicate that changes in σ bonding affect their magnitude, and the nature of the lone pair of electrons at nitrogen is of great importance. The calculated NMR parameters of an adduct of the iminoborane with an N‐heterocyclic carbene, show that the bonding situation around the BN double bond in the adduct is comparable with imines.     

Experimental and theoretical study of the intramolecular C–H···N and C–H···S hydrogen bonding effects in the 1H and 13C NMR spectra of the 2‐(alkylsulfanyl)‐5‐amino‐1‐vinylpyrroles: a particular state of amine nitrogen

In the ¹H NMR spectra of the 1‐vinylpyrroles with amino‐ and alkylsulfanyl groups in 5 and 2 positions, an extraordinarily large difference between resonance positions of the H_A and H_B terminal methylene protons of the vinyl group is discovered. Also, the one‐bond ¹J(C_β,H_B) coupling constant is surprisingly greater than the ¹J(C_β,H_A) coupling constant in pyrroles under investigation, while in all known cases, there was a reverse relationship between these coupling constants. These spectral anomalies are substantiated by quantum chemical calculations. The calculations show that the amine nitrogen lone pair is removed from the conjugation with the π‐system of the pyrrole ring so that it is directed toward the H_B hydrogen. These factors are favorable to the emergence of the intramolecular C–H_B???N hydrogen bonding in the s‐cis(N) conformation. On the other hand, the spatial proximity of the sulfur to the H_B hydrogen provides an opportunity of the intramolecular C–H_B???S hydrogen bonding in the s‐cis(S) conformation. Presence of the hydrogen bond critical points as well as ring critical point for corresponding chelate ring revealed by a quantum theory of atoms in molecules (QTAIM) approach confirms the existence of the weak intramolecular C–H???N and C–H???S hydrogen bonding. Therefore, an unusual high‐frequency shift of the H_B signal and the increase in the ¹J(C_β,H_B) coupling constant can be explained by the effects of hydrogen bonding. Copyright © 2013 John Wiley & Sons, Ltd.     

Temperature dependences of J(C,H) and J(C,D) in 13CH4 and some of its deuterated isotopomers

The nuclear spin—spin coupling constants J(C,H) and J(C,D) have been measured over the temperature range 200–370 K for the methane isotopomers ¹³CH₄, ¹³CH₃D, ¹³CHD₃ and ¹³CD₄. The coupling constants increase with increasing temperature for any one isotopomer and decrease with increasing secondary deuterium substitution at any one temperature. The results are entirely attributable to intramolecular effects and the data have been fitted by a weighted least-squares regression analysis to a spin—spin coupling surface thereby yielding a value for ¹J_e(C,H), the coupling constant at equilibrium geometry, and values for the bond length derivatives of the coupling. We find that ¹J_e(C,H) = 120.78 (±0.05) Hz which is about 4.5 Hz smaller than the observed value in ¹³CH₄ gas at room temperature. Results are also reported for J(H,D) in ¹³CH₃D and ¹³CHD₃ for which no temperature dependence was detected.     

Spin–Spin Artificial DNA Intercalated with Silver Cations: Theoretical Prediction

The indirect nuclear spin–spin coupling constants of Ag⁺ cation intercalated between imidazole rings in DNA chains are calculated by means of DFT with relativistic effects taken into account by the use of the zeroth‐order regular approximation Hamiltonian (DFT‐ZORA). The calculations model how the ¹J(¹⁵N,¹⁰⁹Ag) coupling constant is affected by different types of geometry deformations and by the presence of water, which is simulated by means of the polarizable continuum model and explicitly present water molecules. Calculations for systems containing two and three imidazole pairs are also carried out to model the influence of stacking interactions. The computed ¹J(¹⁵N,¹⁰⁹Ag) spin–spin coupling constant is in the range of 85–105 Hz (depending on the computational model) and is in good agreement with the experimental value (ca. 92 Hz). This coupling constant is very little affected by the presence of solvent, stacking interactions, and geometry deformations. Such behavior is explained by visualization of the coupling path by means of coupling energy density (CED). Bigger models allow the coupling constant between two adjacent silver ions to be computed, and give a value of approximately 1 Hz, which is probably too small to be of practical interest. The ²J(¹⁵N,¹⁵N) value is calculated to be about 2.5 Hz, and is therefore of measurable magnitude.     

Intermolecular Interaction and Magnetic Coupling Mechanism of a Mononuclear Nickel(II) Complex

The mononuclear complex [Ni(HOphen)(OSO₃)(H₂O)₃] · 5H₂O (HOphen = 1, 10‐phenanthrolin‐2‐ol) was prepared and its single structure was determined by X‐ray crystallography. In this complex, the Ni^II ion has a distorted octahedral arrangement. Crystal structure analysis shows that two kinds of π–π stacking interactions and C–H ··· O short contact intermolecular interactions exist among the adjacent complexes. Fitting to the variable‐temperature magnetic susceptibility data gave the magnetic coupling constant, 2J = –0.98 cm^–1. Theoretical calculations, based on density functional theory (DFT) coupling with the broken‐symmetry approach (BS), revealed that the π–π stacking magnetic coupling pathways resulted in weak ferromagnetic interactions with 2J = 4.86 cm^–1 and 2J = 4.16 cm^–1, respectively, for the adjacent Ni^II ions with separations of 8.568(19) Å and 8.749(32) Å, respectively; whereas the magnetic coupling pathway of the C–H ··· O short contact intermolecular interaction led to a weak antiferromagnetic interaction with 2J = –17.62 cm^–1 for the adjacent Ni^II ions with a separation of 10.291(26) Å. The ferromagnetic coupling sign can be explained by the McConnell I spin‐polarization mechanism.     

Selective J‐resolved‐HMQC‐1 and ‐2, new methods for measuring proton–proton coupling constants in strongly coupled spin systems

Efficient pulse sequences for measuring ¹H–¹H coupling constants (J_HH) in strongly coupled spin systems, named selective J‐resolved‐HMQC‐1 and ‐2, have been developed. In the strongly coupled spin systems such as ‐CH₂‐CH_A(OH)‐CH_B(OH)‐CH₂‐, measurements of ³J_HAHB are generally difficult owing to the complicated splitting caused by the adjacent CH₂ protons. For easier and accurate measurements of ³J_HAHB in such a spin system, a selective excitation pulse is incorporated into the J‐resolved HMQC pulse sequence. In the proposed methods, only two strongly coupled protons, H_A and H_B which are excited by a selective pulse, are observed as J‐resolved HMQC signals. The cross peaks of H_A and H_B appear as doublets owing to ³J_HAHB along the F₁ dimension in the selective J‐resolved HMQC‐1 and ‐2 experiments. The efficiency of the proposed pulse sequences has been demonstrated in application to the stereochemical studies of the complicated natural product, monazomycin. Copyright © 2011 John Wiley & Sons, Ltd.     

Can One Assess the π Character of a C–C Bond with the Help of the NMR Spin–Spin Coupling Constants?

Measured one‐bond spin–spin coupling constants (SSCC) ¹J(CC) can be used to describe the nature of the C–C bond, provided one is able to separate the various coupling mechanisms leading to ¹J(CC). The Fermi‐contact (FC) term probes the first‐order density at the positions of the coupling nuclei, whereas the noncontact terms (the paramagnetic spin orbit (PSO) and the spin–dipole (SD) terms) probe the π character of the C–C bond (the diamagnetic spin orbit (DSO) term can mostly be neglected). A model is tested, in which the value of the FC(CC) term is estimated with the help of measured SSCCs ¹J(CH). The difference between the measured J(CC) and the estimated FC(CC) values, Δ(CC)=PSO(CC)+SD(CC)+DSO(CC), provides a semiquantitative measure of the π character of a C–C multiple bond. The applicability and limitations of this approach are discussed by partitioning the four Ramsey terms of the SSCC ¹J(CC) into one‐ and two‐orbital contributions. The FC, PSO, and SD terms of ¹J(CC) are explained and analyzed with regard to their relationship to other C–C bond properties. It is shown that empirical relationships between measured SSCCs and the s character of a bond need reconsideration.     

BASHD‐J‐resolved‐COSY: a new method for measuring proton‐proton spin coupling constants of multiplet signals

An effective pulse sequence for measuring H–H coupling constants, named BASHD‐J‐resolved‐COSY, has been developed. In the spin systems such as –CH_A–CH_B(CH₃)–CH_C–, a methine proton H_B splits into a multiplet owing to several vicinal couplings, resulting in attenuation of its cross‐peak intensity. Therefore, the measurements of ³J_H–H with respect to H_B are generally difficult in the E‐COSY‐type experiments. With the aim of accurate measurements of ³J_H‐H in such a spin system, we have developed a new pulse sequence, which selectively decouples the secondary methyl group. The proposed pulse sequence provides the simplified cross‐peak patterns, which are suitable for reliable measurements of ³J_H‐H in a complicated natural product. Copyright © 2012 John Wiley & Sons, Ltd.     

The mutual effect of a carbonyl polar bond and an endocyclic oxygen on the 1JC‐F coupling constant of fluorinated six‐membered rings

The ¹J_C‐F coupling constant can be useful to probe the conformational landscape of organofluorine compounds and the intramolecular interactions governing the stereochemistry of these compounds. Neighboring oxygen electron lone pairs and a carbonyl group relative to a C─F bond affect this coupling constant in an opposite way, and therefore, analysis of the interactions involving these entities simultaneously indicates which effect dominates ¹J_C‐F. Spin–spin coupling constant calculations for a series of fluorinated tetrahydropyrans, cyclohexanones, and dihydropyran‐3‐ones indicated that an electrostatic/dipolar interaction between the C─F and C═O bonds is more important than the steric interaction between the C─F bond and the oxygen electron lone pairs. An intuitive consequence of such outcome is that this interaction not only drives the coupling constant but can also be taken into account when aiming at the stereochemical control of functionalized organofluorine compounds.     

First example of the correlated calculation of the one‐bond tellurium–carbon spin–spin coupling constants: Relativistic effects,vibrational corrections,and solvent effects

This work reports on the comprehensive calculation of the NMR one‐bond spin–spin coupling constants (SSCCs) involving carbon and tellurium, ¹J(¹²⁵Te,¹³C), in four representative compounds: Te(CH₃)₂, Te(CF₃)₂, Te(C?CH)₂, and tellurophene. A high‐level computational treatment of ¹J(¹²⁵Te,¹³C) included calculations at the SOPPA level taking into account relativistic effects evaluated at the 4‐component RPA and DFT levels of theory, vibrational corrections, and solvent effects. The consistency of different computational approaches including the level of theory of the geometry optimization of tellurium‐containing compounds, basis sets, and methods used for obtainig spin–spin coupling values have also been discussed in view of reproducing the experimental values of the tellurium–carbon SSCCs. Relativistic corrections were found to play a major role in the calculation of ¹J(¹²⁵Te,¹³C) reaching as much as almost 50% of the total value of ¹J(¹²⁵Te,¹³C) while relativistic geometrical effects are of minor importance. The vibrational and solvent corrections account for accordingly about 3–6% and 0–4% of the total value. It is shown that taking into account relativistic corrections, vibrational corrections and solvent effects at the DFT level essentially improves the agreement of the non‐relativistic theoretical SOPPA results with experiment. © 2016 Wiley Periodicals, Inc.     

13C, 1H spin coupling constants of dimethylacetylene

¹³C, ¹H spin coupling constants of dimethylacetylene have been determined by the complete analysis of the proton coupled ¹³C NMR spectrum. For the methyl carbon ¹J(CH) = + 130.6₄ Hz and ⁴J(CH) = + 1.5₈ Hz, and for the acetylenic carbon ²J(CH) = ? 10.34 Hz and ³J(CH) = +4.30 Hz. The ⁵J(HH) long-range coupling constant (+2.79 Hz) between the methyl protons was also determined.     

Is [Cu3(L2)Cl2]2+ a molecule with geometrically spin frustration? DFT study on magnetic competing interaction in hetero-bridged tricopper(II) complex

The theoretical calculations on magnetic exchange interaction of the hetero-bridged tricopper(II) complex [Cu₃(L²)Cl₂]²⁺ and a related binuclear copper(II) model are carried out by using the density functional theory combined with the broken-symmetry approach. Meanwhile, one strategy computationally, so called isolated magnetic pair approach, is suggested to explore the spin frustration from geometry topology in poly-nuclear magnetic systems. It is found that the ferromagnetic coupling (J₂>0) of Cu1–Cu3 pair bridged by double μ–Cl ligands, in nature, is intrinsic, not resulted from geometrically spin frustration in the hetero-bridged tricopper(II) studied. However, in the whole molecule exist two competing contributions of antiferromagnetic and ferromagnetic coupling, and the antiferromagnetic coupling (J₁) from Cu1–(μ–OR)–Cu2 and Cu2–(μ–OR)–Cu3 pairs dominates the magnetic behavior of the whole molecular system. On the other hand, the variation of J₁/J₂ ratio affects significantly on magnetic properties of the system. The calculated effective magnetic moment μ_eff of 2.26μ_B at the OPerdew functional level is compared to experimentally observation of 2.70μ_B in the solution. The briefly analysis of molecular magnetic orbitals demonstrated that the two local magnetic orbitals on Cu1 and Cu3 ions are orthogonal each other, and primarily responsible for the intrinsic ferromagnetic coupling between Cu1–(μ–Cl)₂–Cu3. By comparison of spin population distributions for the Cu-triad and Cu-dimer the validity of the isolated magnetic pair approach is confirmed.     

1,2‐, 1,7‐ and 1,12‐Dicarba‐closo‐dodecaborane(12) Derivatives Revisited by 13C NMR Spectroscopy and DFT Calculations. First Observation of Isotope‐Induced Chemical Shifts 1Δ10/11B(13C), and the Signs and Magnitudes of Coupling Constants 1J(13C,13C) and 1J(13C,11B)

The origin of broadening of ¹³C(carborane) NMR signals of 1,2‐, 1,7‐ and 1,12‐dicarba‐closo‐dodecaboranes(12) and several diphenylsilyl derivatives has been examined in detail and could be traced only partially to unresolved ¹³C–¹¹B spin‐spin coupling. Other contributions to the line widths arise from ¹³C–¹H dipole‐dipole interactions and, in particular, from isotope‐induced chemical shifts ¹Δ^10/11B(¹³C), observed here for carboranes for the first time. In the case of 1‐diphenylsilyl‐1,2‐dicarba‐closo‐dodecaborane(12), the coupling constant ¹J(¹³C,¹³C) = 9.3 Hz was measured in natural abundance of ¹³C. The small value of this coupling constant and its negative sign is predicted by calculations based on optimised structures [B3LYP/6‐311+G(d,p) level of theory] of the parent carboranes and 1‐silyl‐1,2‐dicarba‐closo‐dodecaborane(12) as a model compound [calcd. ¹J(¹³C,¹³C) = –10.5 Hz]. Calculated coupling constants ¹J(¹³C,¹¹B) are small (<7 Hz), in contrast to published assumptions, and of either sign, whereas ¹J(¹¹B,¹¹B) are all positive and range up to 15 Hz.