Symmetry components analysis of nuclear spin–spin coupling constants

Molecular symmetry properties are used to define “normal” spin–spin coupling constants corresponding to some irreducible representations of the symmetry point group of the molecule. The relationship between these normal coupling constants and the measured ones is established in closed form for the most common cases. The Ramsey perturbation formula is analysed into symmetry components by means of the Winger–Eckart theorem. Both contributions predicted by the molecular-orbital method, i. e. direct coupling via σ electrons and indirect coupling via σ–π interaction are studied. Numerical calculations for the coupling constants of ethane, ethylene and acetylene were carried out without the mean excitation energy approximation by using SCF ? MO wave functions; overlap between atomic orbitals is systematically taken into account by calculating coupling constants. Theoretical and experimental results are compared in terms of symmetry components.     

Geometric approximation to nuclear spin–spin coupling constants in the water molecule

The geometric aproximation is used within the framework of triple perturbation theory to evaluate the contributions to nuclear spin–spin coupling constants in the water molecule provided by the Fermi contact, the spin–orbit, and the spin–dipolar interactions. The results, obtained with SCF wave functions expanded over Gaussian basis sets of increasing quality, are compared with corresponding coupled Hartree–Fock estimates. The limits of the geometric approximation to coupling constants are discussed.     

Substituent effects on nuclear spin–spin carbon–carbon coupling constants in derivatives of acetylene

¹J(¹³C?¹³C) nuclear spin–spin coupling constants in derivatives of acetylene have been measured from natural abundance ¹³C NMR spectra and in one case (triethylsilyllithiumacetylene) from the ¹³C NMR spectrum of a ¹³C-enriched sample. It has been found that the magnitude of J(C?C) depends on the electronegativity of the substituents at the triple bond. The equation ¹J(¹³C?¹³C) = 43.38 E_x + 17.33 has been derived for one particular series of the compounds Alk₃SiC?CX, where X denotes Li, R₃Sn, R₃Si, R₃C, I, Br or Cl. The ¹J(C?C) values found in this work cover a range from 56.8 Hz (in Et₃SiC?Li) to 216.0 Hz (in PhC?CCI). However, the ¹J(C?C) vs E_x equation combined with the Egli–von Philipsborn relationship allows the calculation of the coupling constants in Li₂C₂ (32 Hz) and in F₂C₂ (356 Hz). These are probably the lowest and the highest values, respectively, which can be attained for ¹J(CC) across a triple bond. The unusually large changes of the ¹J(C?C) values are explained in terms of substituent effects followed by a re-hybridization of the carbons involved in the triple bond. INDO FPT calculations performed for two series of acetylene derivatives, with substituents varied along the first row of the Periodic Table, corroborate the conclusions drawn from the experimental data.     

Long-range nuclear spin–spin coupling between selenium-77 and phosphorus-31 in biphosphorus compounds

The coupling constants ⁿJ(⁷⁷Se³¹P), n = 1–4, have been measured in the proton-decoupled ³¹P NMR spectra of a range of diphosphorus selenides and diselenides. ³¹P–{¹H, ³¹P} and ³¹P–{¹H, ⁷⁷Se} triple resonance experiments have been used to establish the signs of the coupling constants, and it is found that both the magnitudes and signs depend upon the stereochemical relationship of the coupled nuclei.     

The additivity of NMR carbon–carbon spin–spin coupling constants

Fluorene-9-¹³C, fluorenone-9-¹³C, acenaphthenone-11-¹³C, acenaphthenone-12-¹³C, 1-methylcyclopentanol-1-¹³C and 1-methylcyclopentene-1-¹³C were synthesized to obtain J(CC) values between the natural carbons and the labeled carbons. Each of these compounds possessed at least one asymmetric dual-path coupling, i.e., coupling between the labeled carbon and another carbon via simultaneous two- and three-bonded coupling paths. Model ¹³C-labeled compounds were synthesized where necessary to give expected values of the constituent mono-path couplings. Values of these dual-path couplings (²⁺³)J suggested that the observed value is the (at least approximate) algebraic sum of the two constituent J values.     

Some INDO calculations of fluorine-nitrogen spin–spin coupling constants

INDO parameterized calculations of ⁿJ(¹⁹F¹⁵N) are reported where n=1, 2, 3, 4 and 5. The calculations are performed within the sum-over-states perturbation and self-consistent perturbation frameworks. In general, satisfactory agreement between both sets of calculated results and the available experimental data is obtained. All of the ¹ J(¹⁹F¹⁵N) and ⁴J(¹⁹F¹⁵N) couplings can be of either sign. Most of the couplings considered are dominated by the contact contribution but the non-contact interactions can be very important in certain cases.     

Nuclear spin–spin coupling between 15N and 13C in an azomethine ylide and related compounds

¹³C? ¹⁵N coupling constants of a stable azomethine ylide, a 2-aza-1,3-diene and an O-tosyloxime have been measured. The large one-bond coupling constants (21·3 and 21·6 Hz) observed for the azomethine ylide prove the dipolar structure of this compound. For the other two compounds, two-bond coupling constants are used to derive the stereochemistry at the C,N double bond.     

One-bond carbon–carbon spin–spin coupling constants: A data summary

A summary of all the one-bond carbon–carbon spin–spin coupling constants, Known up to the beginning of 1980, is given in diagrammatic form.     

Signs of heteronuclear spin–spin coupling constants in 15N-acetamide

By using digital deconvolution to improve spectral resolution, earlier NMR studies on ¹⁵N-enriched acetamide have been revised and extended to determine the signs of the heteronuclear spin-spin coupling constants. ¹J(¹³CO¹⁵N), ²J(¹³CH₃¹⁵N) and ³J(C¹H₃¹⁵N) are negative while ³J(¹H¹³CH₃)>0. The results, interpreted on the basis of the ‘selective decoupling’ formalism, were confirmed by computer simulation of the double resonance spectra. It is shown that ²J(¹H-α¹³CO) is significantly larger than ²J(¹H^{N 13}CO). Thus, jointly with {¹H-β}-¹³C′ double resonance experiments, {¹H-α}-¹³C′ experiments ought to be most helpful when assigning peptide group carbonyl resonances. The study provides valuable information for the interpretation of heteronuclear coupling constants in polypeptides.     

Carbon-13, 1H spin–spin coupling VI—biphenylene

¹³C, ¹H coupling constants for biphenylene have been obtained from the analysis of the ¹³C NMR spectrum of the natural abundance α-¹³C- and β-¹³C-isotopomers. The various mechanisms responsible for the observed results are discussed.     

NMR spin–spin coupling constants in hydrogen‐bonded glycine clusters

The influence of the hydrogen bond formation on the NMR spin–spin coupling constants (SSCC), including the Fermi contact (FC), the diamagnetic spin‐orbit, the paramagnetic spin‐orbit, and the spin dipole term, has been investigated systematically for the homogeneous glycine cluster, in gas phase, containing up to three monomers. The one‐bond and two‐bond SSCCs for several intramolecular (through covalent bond) and intermolecular (across the hydrogen‐bond) atomic pairs are calculated employing the density functional theory with B3LYP and KT3 functionals and different types of extended basis sets. The ab initio SOPPA(CCSD) is used as benchmark for the SSCCs of the glycine monomer. The hydrogen bonding is found to cause significant variations in the one‐bond SSCCs, mostly due to contribution from electronic interactions. However, the nature of variation depends on the type of oxygen atom (proton‐acceptor or proton‐donor) present in the interaction. Two‐bond intermolecular coupling constants vary more than the corresponding one‐bond constants when the size of the cluster increases. Among the four Ramsey terms that constitute the total SSCC, the FC term is the most dominant contributor followed by the paramagnetic spin‐orbit term in all one‐bond interaction.     

C and H nuclear magnetic shielding and spin–spin coupling constants of C-enriched bromomethane in the gas phase

¹³C and ¹H NMR spectral parameters are investigated for ¹³CH₃Br in gaseous matrices. It is found that both the ¹³C and ¹H chemical shifts of ¹³CH₃Br are linearly dependent on solvent density. Similar dependence is also detected for one-bond spin–spin coupling, ¹J(CH). For the first time the ¹³C and ¹H magnetic shielding constants and ¹J(CH) spin–spin coupling are obtained for an isolated ¹³CH₃Br molecule together with the coefficients responsible for solute–solvent molecular interactions in gaseous matrices. The present experimental results confirm the accuracy of some recent ab initio calculations of nuclear magnetic shielding performed for bromomethane.     

A note on the calculations of spin–spin coupling constants involving carbon

Sum-over-states perturbation and self-consistent perturbation calculations of ⁿJ(CC) using standard INDO parameters are discussed. Calculated values of ¹J(OC) for acetone are reported. In general it seems that the sum-over-states calculations are the more reliable. The importance of including non-contact contributions in the calculation of couplings between carbon and nuclei with larger values of 〈r^?3〉 is stressed.     

Benchmark calculations of 29Si–1H spin–spin coupling constants across double bond

Benchmark calculations of geminal and vicinal ²⁹Si–¹H spin–spin coupling constants across double bond in three reference alkenylsilanes have been carried out at both DFT and SOPPA levels in comparison with experiment. At the former, four density functionals, B3LYP, B3PW91, PBE0 and KT3, were tested in combination with five representative basis sets. At the latter, three main SOPPA‐based methods, SOPPA, SOPPA(CC2) and SOPPA(CCSD), were examined in combination with the same series of basis sets. On the whole, the wavefunction methods showed much better results as compared to DFT, with the most efficient combination of SOPPA/cc‐pVTZ‐su2 characterized by a mean absolute error of only 0.4 Hz calculated for a set of nine coupling constants in three compounds with a sample span of around 40 Hz. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural trends of 29Si–1H spin–spin coupling constants across double bond

The calculations of geminal and vicinal ²⁹Si–¹H spin–spin coupling constants across double bond in 15 alkenylmethylsilanes and alkenylchlorosilanes were carried out at the second‐order polarization propagator approach level in a good agreement with experiment. Two structural trends, namely, (i) the geometry of the coupling pathway and (ii) the effect of the electrowithdrawing substituent, have been interpreted in terms of the natural J‐coupling analysis within the framework of the natural bond orbital approach. Thus, the marked difference between cisoidal and transoidal ²⁹Si–¹H spin–spin coupling constants across double bond was accounted for the delocalization contributions including bonding and antibonding Si–C and C–H orbitals, whereas the chlorine effect was explained in terms of the steric contributions including bonding Si–Cl orbitals. Copyright © 2012 John Wiley & Sons, Ltd.     

Relativistic effects in the one‐bond spin–spin coupling constants involving selenium

One‐bond spin–spin coupling constants involving selenium of seven different types, ¹ J(Se,X), X = ¹H, ¹³C, ¹⁵ N, ¹⁹ F, ²⁹Si, ³¹P, and ⁷⁷Se, were calculated in the series of 14 representative compounds at the SOPPA(CCSD) level taking into account relativistic corrections evaluated both at the RPA and DFT levels of theory in comparison with experiment. Relativistic corrections were found to play a major role in the calculation of ¹ J(Se,X) reaching as much as almost 170% of the total value of ¹ J(Se,Se) and up to 60–70% for the rest of ¹ J(Se,X). Scalar relativistic effects (Darwin and mass‐velocity corrections) by far dominate over spin–orbit coupling in the total relativistic effects for all ¹ J(Se,X). Taking into account relativistic corrections at both random phase approximation and density functional theory levels essentially improves the agreement of theoretical results with experiment. The most ‘relativistic’ ¹ J(Se,Se) demonstrates a marked Karplus‐type dihedral angle dependence with respect to the mutual orientation of the selenium lone pairs providing a powerful tool for stereochemical analysis of selenoorganic compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

Carbon-13, proton spin–spin coupling constants in some 2-substituted propanes

Carbon-13, proton coupling constants have been measured in eighteen different 2-substituted propanes. ¹J(C-2,H) shows variations similar to those observed previously for monosubstituted methanes. ²J(C-2,H) is essentially independent of the substituent at C-2, while ²J(C-1,H) varies over a range of at least 5 Hz. The latter coupling constant becomes more positive as the electronegativity of the substituent increases while ³J(CH) decreases as the electronegativity of the substituent increases. The observed trends in ⁿJ(CH) are compared with those calculated using semi-empirical molecular orbital theory at the INDO level of approximation.     

Relativistic theory for indirect nuclear spin–spin couplings within the polarization propagator approach

We present a relativistic theory for the nuclear spin–spin coupling tensor within the polarization propagator approach using the particle-hole Dirac–Coulomb–Breit Hamiltonian and the full four-component wave function. We give explicit expressions for the coupling tensor in the random-phase approximation, neglecting the Breit interaction. A purely relativistic perturbative electron–nuclear Hamiltonian is used and it is shown how the single relativistic contribution to the coupling tensor reduces to Ramsey's three second-order terms (Fermi contact, spin–dipole, and paramagnetic spin–orbit) in the nonrelativistic limit. The principal propagator becomes complex and the leading property integrals mix atomic orbitals of different parity. The well-known propagator expressions for the coupling tensor in the nonrelativistic limit is obtained neglecting terms of the order c^?n (n ? 1). © 1993 John Wiley & Sons, Inc.     

Ultra long range 19F?19F spin–spin coupling

The observation of long range (10–14 bond) spin–spin coupling between fluorine nuclei (which are very far apart in space) is used to provide information about electronic interactions in bridged dinuclear aromatic compounds.     

Graphical unitary group approach to spin–spin interaction

A detailed exposition of spin–spin operator matrix elements is presented in the context of the graphical unitary group approach (GUGA ) to atomic and molecular physics and quantum chemistry. A compendium of subgraph types and formulae is given. Aspects of computer implementation within the structure of the Columbus CI programs is discussed.