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.     

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.     

Long range H,H coupling constants in cycloheptatrienes

The ¹H NMR spectra of 1,6-dicarbomethoxycyclohepta-1,3,5-triene ( 2 ) and 3,4-benzocyclohepta-1,3,5-triene ( 3 ) have been analysed in terms of chemical shifts and coupling constants. A method for the assignment of δ(AA′) and δ(BB′) in AA′BB′ systems, based on the observation of ¹³C satellites in the ¹H NMR spectrum, is described. For J(1,5) in 3 , a negative sign was established. Spin tickling experiments were used to determine the positive sign for J(2,5) in 2 and the negative sign for J(2,7) in 3. The conformation of 3 is 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 cyano C–H coupling constants in some cyanopyridines and benzonitriles

Cyano carbon-ring coupling interactions in 12 benzonitriles and three cyanopyridines have been examined. Correlations between ⁿJ_CH and ⁿJ_HH (n=3 and 4) are given. Unresolved weak ⁵J-para coupling limits the application of these splittings in structural determination studies.     

Characterization of coupling constants to nitrogen. Carbon-13 chemical shifts and carbon–nitrogen coupling constants of substituted benzaldoximes

Carbon-13 chemical shifts and ¹³C?¹⁵N coupling constants of substituted benzaldoximes and of two non-aromatic oximes have been determined. The coupling constants display little variation as a function of the nature or position of substitution, which suggests that perturbations in the π electron distribution have little effect. The values are compared with the markedly different ones reported for mesitaldoxime, and, in conjunction with the observed solvent effects, are discussed within the Schulman-Venanzi framework for assessing the role of the lone-pair.     

Self-consistent perturbation-INDO calculations of nuclear magnetic resonance carbon–carbon coupling constants for methylcycloalkanes

One bond ¹³C,¹³C coupling constants have been calculated for some methylcycloalkanes, as well as for 2-methylbutane, using the self-consistent perturbation theory as formulated by Blizzard and Santry at the INDO (intermediate neglect of differential overlap) level of approximation. Together with previously published experimental data, the results can be interpreted satisfactorily on the basis of the Walsh model for cyclopropane and the known s character relationship ¹J(¹³C¹³C) = 575·s(i)· s(j).     

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 3. Polyhedranes

High‐level ab initio calculations of carbon–carbon coupling constants were carried out in tetrahedrane, prismane and cubane using the SOPPA (Second‐Order Polarization Propagator Approach) computational scheme, in good agreement with available experimental data. It was found that SOPPA performs perfectly well in combination with Dunning's correlation‐consistent basis sets augmented with inner core functions; however, no improvement was observed on adding tight s‐functions. The utmost importance of electronic correlation effects decreasing the total values of computed J(C,C) in the title compounds by a factor of ～2.0–2.5 was found. Unknown values of J(C,C) in the title polyhedranes were predicted with high reliability and the latter were treated in terms of s‐characters of carbon–carbon bonds based on the additive scheme of coupling pathways. All three compounds under study showed decreased s‐characters of their carbon–carbon bonds, which is the result of their remarkable steric strain. Copyright © 2003 John Wiley & Sons, Ltd.     

Long range phosphorus-phosphorus coupling constants in bis(phosphorylhydroxymethyl)benzene derivatives

Long range spin-spin couplings found between two phosphorus atoms are quite rare phenomena. A new example of such a coupling through seven bonds is described for 1-[(diethoxyphosphoryl)butyryloxymethyl]-4-[(diethoxyphosphoryl)hydroxymethyl]benzene and 1,4-bis[phosphorylhydroxymethyl]benzene and through six bonds for tetraethyl phenylene-1,3-(bishydroxymethylphosphonate). Coupling constants in this system are also well predicted by theoretical studies.     

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 2. Strained polycarbocycles

High‐level non‐empirical calculations of carbon–carbon spin–spin coupling constants in a series of strained polycarbocycles have been carried out, in excellent agreement with available experimental data. The utmost importance of electronic correlation effects in this case has been demonstrated and it has been shown that the Second‐Order Polarization Propagator Approach (SOPPA) is an adequate method to account for those effects. It has been demonstrated that the most reliable basis sets to calculate J(C,C) at the SOPPA level are the correlation‐consistent basis sets of Dunning and co‐workers augmented with inner core s‐functions or decontracted in their s‐parts. The nature of the unusual bridgehead–bridgehead bonds in bicyclobutane and propellane in terms of s‐characters of bonding hybrids and also the hybridization effects in spiropentane are discussed based on the arguments derived from the current calculations of J(C,C) in the title compounds. The values of the unknown J(C,C) in propellane and spiropentane are predicted with high reliability. Copyright © 2003 John Wiley & Sons, Ltd.     

Investigation of two‐ and three‐bond carbon–hydrogen coupling constants in cinnamic acid based compounds

Two‐ and three‐bond coupling constants (²J_HC and ³J_HC) were determined for a series of 12 substituted cinnamic acids using a selective 2D inphase/antiphase (IPAP)‐single quantum multiple bond correlation (HSQMBC) and 1D proton coupled ¹³C NMR experiments. The coupling constants from two methods were compared and found to give very similar values. The results showed coupling constant values ranging from 1.7 to 9.7 Hz and 1.0 to 9.6 Hz for the IPAP‐HSQMBC and the direct ¹³C NMR experiments, respectively. The experimental values of the coupling constants were compared with discrete density functional theory (DFT) calculated values and were found to be in good agreement for the ³J_HC. However, the DFT method under estimated the ²J_HC coupling constants. Knowing the limitations of the measurement and calculation of these multibond coupling constants will add confidence to the assignment of conformation or stereochemical aspects of complex molecules like natural products. Copyright © 2016 John Wiley & Sons, Ltd.     

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 4: Bicycloalkanes

A systematic study of the one‐bond and long‐range J(C,C), J(C,H) and J(H,H) in the series of nine bicycloalkanes was performed at the SOPPA level with special emphasis on the coupling transmission mechanisms at bridgeheads. Many unknown couplings were predicted with high reliability. Further refinement of SOPPA computational scheme adjusted for better performance was carried out using bicyclo[1.1.1]pentane as a benchmark to investigate the influence of geometry, basis set and electronic correlation. The calculations performed demonstrated that classical ab initio SOPPA applied with the locally dense Dunning's sets augmented with inner core s‐functions used for coupled carbons and Sauer's sets augmented with tight s‐functions used for coupled hydrogens performs perfectly well in reproducing experimental values of different types of coupling constants (the estimated reliability is ca 1–2 Hz) in relatively large organic molecules of up to 11 carbon atoms. Additive coupling increments were derived for J(C,C), J(C,H) and J(H,H) based on the calculated values of coupling constants within SOPPA in the model bicycloalkanes, in reasonably good agreement with the known values obtained earlier on pure empirical grounds. Most of the bridgehead couplings in all but one bicycloalkane appeared to be essentially additive within ca 2–3 Hz while bicyclo[1.1.1]pentane demonstrated dramatic non‐additivity of ?14.5 Hz for J(C,C), +16.6 Hz for J(H,H) and ?5.5 Hz for J(C,H), in line with previous findings. Non‐additivity effects in the latter compound established at the SOPPA level should be attributed to the through‐space non‐bonded interactions at bridgeheads due to the essential overlapping of the bridgehead rear lobes which provides an additional and effective non‐bonding coupling path for the bridgehead carbons and their protons in the bicyclopentane framework. Copyright © 2003 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.     

Aza-polycyclic aromatic hydrocarbons: 1—Elucidation of the regiochemistry of 1,2,3,4-tetrahydroazabenz-[a]anthracene-7,12-diones by long-range carbon–proton coupling constants

The ¹³C NMR spectra of 5,8-quinolinedione, 6-chloro-5,8-quinolinedione and 7-chloro-5,8-quinolinedione have been examined in detail. Utilization of long-range proton-carbon coupling constants have allowed the unambiguous identification of the regioisomeric 8-aza-1,2,3,4-tetrahydrobenz[a]anthracene-7,12-dione and 11-aza-1,2,3,4-tetrahydrobenz[a]anthracene-7,12-dione.     

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 1. Three‐membered rings

The carbon–carbon indirect nuclear spin–spin coupling constants in cyclopropane, aziridine and oxirane were investigated by means of ab initio calculations at the RPA, SOPPA and DFT/B3LYP levels. We found that the carbon–carbon couplings are by far dominated by the Fermi contact term. Our best SOPPA and DFT results are in a very good agreement with each other and with the experimental values, whereas calculations at the RPA level of theory strongly overestimate the carbon–carbon couplings. Significant differences in the basis set dependence of the calculated carbon–carbon coupling constants obtained with either wavefunction method, RPA or SOPPA, or the density functional method, DFT/B3LYP, are observed. The SOPPA results depend much more strongly on the quality of the basis set than the results of DFT/B3LYP calculations. The medium‐sized core‐valence basis sets cc‐pCVTZ and even cc‐pCVDZ were found to perform fairly well at the SOPPA level for the one‐bond carbon–carbon couplings investigated here. Copyright © 2002 John Wiley & Sons, Ltd.     

Long range 13C?1H coupling constants. III—methylpyridines

Proton coupled carbon-13 NMR spectra of eleven mono-, di- and trimethylpyridines were analysed on a first order basis. The long range ¹³C? ¹H coupling constants are similar to those observed for pyridine and cyanopyridines.     

BASHD‐J‐resolved‐HMBC,an efficient method for measuring proton–proton and heteronuclear long‐range coupling constants

Natural products often possess various spin systems consisting of a methine group directly bonded to a methyl group (e.g. –CH_a–CH_b(CH₃)–CH_c–). The methine proton H_b splits into a broadened multiplet by coupling with several vicinal protons, rendering analysis difficult of ⁿJ_C–H with respect to H_b in the J‐resolved HMBC‐1. In purpose of the reliable and easy measurements of ⁿJ_C–H and ⁿJ_H–H in the aforesaid spin system, we have developed a new technique, named BASHD‐J‐resolved‐HMBC. This method incorporates band selective homo decoupled pulse and J‐scaling pulse into HMBC. In this method, high resolution cross peaks can be observed along the F₁ axis by J‐scaling pulse, and band selective homo decoupled pulse simplified multiplet signals. Determinations of ⁿJ_C–H and ⁿJ_H–H of multiplet signals can easily be performed using the proposed pulse sequence. Copyright © 2013 John Wiley & Sons, Ltd.     

The 13C,H coupling constants in structural and conformational analysis. III.. Long-range carbon–hydroxyl proton couplings as evidence of hydrogen bonding in some acylphloroglucinols

Proton coupled ¹³C NMR spectra have been recorded for some acylphloroglucinol derivatives. Significant couplings over two, three and four bonds were observed between the hydroxyl proton and aromatic carbons for those compounds where the hydroxyl group is hydrogen bonded strongly enough to the carbonyl carbon of the acyl side chain. Typical values were ²J = 4.8 Hz, and ³J = 5.6 Hz or 6.7 Hz corresponding to dihedral angles of c. 0° and c. 180°, respectively; the dihedral angle is defined as the angle between the O—H bond and the plane of the aromatic ring. A stereospecific ⁴J(COH) value of 1.2 Hz for a ‘W’ arrangement of coupled atoms was also found. An interesting example of ‘virtual’ J(CH) coupling was observed in the proton coupled spectrum of 1-butyrylphloroglucinol 2-monomethyl ether in acetone-d₆ caused by the accidentally equal chemical shifts of the two ring protons.     

Long range 13C?13C coupling constants. A review

A large number of ¹³C? ¹³C coupling constants from a diversity of compounds are now available. Attempts have been made to classify this information in order to illustrate how these data are obtained, how signs are determined and how both two- and three-bond couplings can lead to structural information. Coupling constants in aromatic compounds are now well documented, substituent effect trends have been established and correlations with bond orders are noticed. Comparison of ¹³C? ¹³C couplings with ¹³C? ¹H couplings is mentioned. Theoretical calculations are dealt with, and these can now be properly evaluated as both magnitudes and signs of the experimental couplings are known. Finally, the occurrence of long range couplings in biosynthetic material is briefly surveyed.