1H and 13C NMR study of α-acetylenic PIII and PIV derivatives. Signs and magnitudes of J(P?C) and J(P?H)

All J(P? H) and J(P? C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R₂P(X)? C?C? H and R₂P(X)? C?C? CH₃ (X ? oxygen, lone pair and R ? C₆H₅, N(CH₃)₂, OC₂H₅, N(C₆H₅)₂, Cl) from ¹H and ¹³C NMR spectra. In P^IV derivatives the following signs are obtained: ¹J(P? C)+, ²J(P? C)+, ³J(P? C)+, ³J(P? H)+, ⁴J(P? H)? . Linear relations are observed between ¹J(P? C), ²J(P? C) and ³J(P? C) versus ³J(P? H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for ¹J(P? C) and ²J(P? C). In P^III derivatives these signs are: ¹J(P? C)- and +, ²J(P? C)+, ³J(P? C)-, ³J(P? H)-, ⁴J(P? H)+. Only ³J(P? C) and ³J(P? H) reflect a small contribution of the Fermi contact term while in ¹J(P? C) and ²J(P? C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.     

Synthese und NMR-Spektren einiger 13C-markierter Thio- und Seleno-äther, -acetale und -orthoester

Synthesis and NMR Spectra of Some ¹³C-Labelled Thio- and Seleno-ethers, -acetals, and -orthoesters Twenty-seven different open-chain and cyclic derivatives (RX)_nCH_4-n and (RX)_nCH_3-nR′ with n = 1?3, X = S or Se, R,R′ = alkyl or aryl, 1,3,5-trithiane, and bis-(dimethylsulfonio)methane and -methanide with single or multiple ¹³C-labelling have been synthesized. The ¹³C-NMR spectra of the sulfur and selenim compounds have been measured, and the dependence of the chemical shifts (δ_c) and coupling constants [′J(C,H), ′J(Se,C)] from the substitution pattern in discussed (Fig. 1) and compared with the polyhalogeno-methanes (Fig. 2).     

Carbon-13 NMR studies of monohydroxylated and monochlorinated derivatives of Z- and E-p-menthanes

J(¹³C¹H) coupling constants for some methyl- and aminopyrimidines have been determined by ¹³C NMR. Both the one-bond and long-bond and long-range coupling constants follow general trends which can be summarized in a few simple rules. In particular, the ³J(C-i,H) coupling constants between a ring carbon C-i and the ring protons are larger than the ²J(C-i,H) coupling constants. The opposite is observed for the couplings between the ring carbons and the methyl protons: ³J(C,Me). These general rules are very useful for the assignment of resonances in complex ¹³C spectra of pyrimidines and seem to be valid for other 6-membered aromatic nitrogen heterocycles. Furthermore, the additivity of substituent effects on ¹J (CH) for monosubstituted pyrimidines allows the estimation of ¹J (CH) for polysubstituted pyrimidines with a very good accuracy.     

Substituenteneffekte auf die NMR-Spektren von Pentafulvenen. (13C, 13C)-NMR-Kopplungskonstanten (1J(C,C))

Substituent Effects on NMR Spectra of Pentafulvenes. ¹³C, ¹³C-NMR Coupling Constants (¹J(C, C)) ¹H- and ¹³C-NMR spectra of 6-monosubstituted pentafulvenes 1 – 8 have been analysed, and ¹J(C, C) coupling constants have been determined from ID-inadequate spectra of ¹³C satellites. It turns out that ¹³C,¹³C coupling constants of the ring C-atoms, and especially J(1,2)/J(3,4) and J(2,3), reflect the extent of π delocalisation in the fulvene ring. With increasing electron-donating capacity of the substituent R, J(1,2)/J(3,4) values are decreasing, while J(2,3) (and J(1,5)/J(4,5) as well) are increasing, and linear correlations of Hammett substituent constants σ⁺ and ¹J(C,C) values are obtained.     

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.     

1H and 31P nuclear magnetic resonance spectra of compounds containing the PIII?N?PV skeleton

The ¹H and ³¹P NMR spectra of a series of compounds containing the P^III-N-P^V skeleton including Cl₂PNMeP(Z)Cl₂ (Z?O or S), Cl₂P·NMe·P(O)CINMe₂, P₄(NMe)₆Z_n (Z?S, n = 1?3; Z?Se, n = 1), XP(NBu^t)₂P(Z)X (X?Cl, Z?O or S; X?OMe, Z?S or Se; X?NMe₂, Z?S or Se; X?NEt₂, Z?Se), (X?O or S), and Ph₂PNRP(S)Ph₂ (R?Me, Et) have been obtained. ¹H-{³¹P} double resonance, and in selected cases, ³¹P-{¹H, ⁷⁷Se} and ³¹P-{¹H, ³¹P} triple resonance experiments, indicate that ²J(P^III NP^V) is positive in acyclic compounds, negative in most cyclic or cage compounds, and furthermore, is related to the conformation adopted by the P^III-N bond.     

Group IV organometal derivatives of pyridine. I—A 1H and 13C NMR investigation of trialkylmetal derivatives of pyridine

The proton and carbon-13 NMR spectra of thirteen trialkylmetal derivatives of pyridine, several of which were previously unknown, have been recorded and analysed. The proton NMR spectra show variations in proton chemical shifts but not in proton-proton coupling constants when the metal substituent is changed; the ring proton-metal coupling constants ⁿJ(M? H) in the tin and lead derivatives correspond closely with the corresponding proton-proton couplings ⁿJ(H? H) in pyridine. The carbon-13 chemical shifts of the carbons bound to the metal can apparently be correlated with the electron-donating ability of the trialkylmetal group. In the trimethylstannylpyridines the value of ¹J(Sn? C_ring) varies greatly with the position of the Me₃Sn group.     

Chalcogen–acetylide interaction and unusual reactivity of coordinated acetylide with water: synthesis and characterisation of [(η5-C5R5)Fe3(CO)6(μ3-E)(μ3-ECCH2RI)] (R=H,Me; RI=Ph,Fc; E=S,Se) and [(η5-C5R5)MoFe2(CO)6(μ3-S)(μ-SCCH2Ph)] (R=H,Me)

Photolysis of a benzene solution containing [Fe₃(CO)₉(μ₃-E)₂] (E=S, Se), [(η⁵-C₅R₅)Fe(CO)₂(CCR^I)] (R=H, Me; R^I=Ph, Fc), H₂O and Et₃N results in formation of new metal clusters [(η⁵-C₅R₅)Fe₃(CO)₆(μ₃-E)(μ₃-ECCH₂R^I)] (R=H, R^I=Ph, E=S 1 or Se 2; R=Me, R^I=Ph, E=S 3 or Se 4; R=H, R^I=Fc, E=S 5; R=Me, R^I=Fc, E=S 6 or Se 7). Reaction of [Fe₃(CO)₉(μ₃-S)₂]with [(η⁵-C₅R₅)Mo(CO)₃(CCPh)] (R=H, Me), under same conditions, produces mixed-metal clusters [(η⁵-C₅R₅)MoFe₂(CO)₆(μ₃-S)(μ-SCCH₂Ph)] (R=H 8; R=Me 9). Compounds 1–9 have been characterised by IR and ¹H and ¹³C-NMR spectroscopy. Structures of 1, 5 and 9 have been established crystallographically. A common feature in all these products is the formation of new C-chalcogen bond to give rise to a (ECCH₂R^I) ligand.     

Substituent Effects on π‐Bond Delocalization of Fulvenes and Fulvalenes. Are Fulvenes Aromatic?

The influence of exocyclic substituents on π‐delocalization of pentafulvenes 2 , heptafulvenes 3 , and nonafulvenes 4 has been investigated. Pentafulvenes 2 : Changes of bond lengths (induced by exocyclic substituents R¹ and R² of 2 ) are reflected by systematic changes of ³J(H,H) (Fig. 2) as well as of ¹J(C,C) coupling constants (Fig. 4), so that linear correlations of σ_p⁺ vs. ³J(H,H) and ¹J(C,C) coupling constants were obtained. Plots of that type are very useful for determining the extent of π‐delocalization of various pentafulvalenes 5 – 8 (Figs. 6 and 12). Charge density effects of pentafulvenes and pentafulvalenes were observed by substituent‐induced shifts of the ring C‐atoms (Fig. 5). Heptafulvenes 3 : Contrary to planar pentafulvenes, heptafulvenes did not show any linear correlations of σ_p⁺ vs. ³J(H,H)‐plots (Fig. 8) or σ_p⁺ vs. δ(¹³C)‐plots (Fig. 9), although substituents R¹, R² clearly influenced ³J(H,H)‐coupling constants as well as ¹³C chemical shifts of the ring H‐atoms and ring C‐atoms. In the NMR spectra of ‘heptafulvenes with inverse ring polarization’ (in the lower range of Fig. 8), ³J(H,H)‐coupling constants were strongly alternating and were barely influenced by exocyclic substituents. This supported a boat conformation of the corresponding heptafulvenes. In the range of Hammett σ_p⁺‐values above ?0.5 to 0, strong substituent effects started to be effective, and a nearly linear approach of ³J(H,H)‐coupling constants J(2,3)/J(4,5) and J(3,4) was observed. This meant that, as soon as heptafulvenes were planar or nearly planar, there existed similar substituent effects as for planar pentafulvenes. – A similar ‘turning point’ was observed in plots of σ_p⁺ vs. ¹³C‐chemical shifts around σ_p⁺=0 (Fig. 9): In the range of strong electron‐accepting groups (above σ_p⁺=1), there was a marked substituent‐induced high‐frequency shift which strongly decreased in the series C(7)>C(2)/C(5)>C(3)/C(4), while C(1)/C(6) was barely influenced. Nonafulvenes 4 : Most nonafulvenes are non‐planar olefins with strongly alternating vicinal H,H‐coupling constants. This has been convincingly shown by the high‐resolution ¹H‐NMR spectrum of 10‐dimethylaminononafulvene ( 4c , Fig. 10), which was not planar but contained a nearly planar (E)‐dienamine substructure of the segment C(7)?C(8)? C(9)?C(10)? NMe₂ according to the NMR data. Only with very strong π‐donors (like two dimethylamino groups in 4b ), planarization of the nine‐membered ring could be observed at low temperatures (Fig. 10). Finally, the first stable nonatriafulvalene (11,12‐bis(diethylamino)nonatriafulvalene ( 10 )) existed in the planar dipolar form in the whole temperature range and even in unpolar solvents.     

Direct and indirect substituent effects on 1J(CH) in vinyl derivatives and related compounds

The variation in the one–bond couplings ¹J(CH) in vinyl derivatives with substituent has been examined. For the geminal proton ¹J correlates very badly with substituent electronegativity but extremely well with σ_I, if conjugating substituents are excluded. In the case of halogen substituents the marked stereospecificity of ¹J(CH) for the cis and trans protons can be rationalised in terms of an intrinsic dependence of π_CH on the dihedral angle between the coupling atoms and the perturbing substituent, with an additional positive increment to the cis coupling due to direct interaction of the substituent non-bonding electrons or to orbital circulation of the substituent electrons. The intrinsic specificity of β-substituent effects on ¹J(CH) is also found in analogous compounds containing C?N and C?O bonds.     

Nuclear magnetic resonance spectroscopy. Analysis of the 1H and 13C spectra of Br13CH213CH2Br

The ¹H and ¹³C NMR spectra of 1,2-dibromoethane-¹³C₂ have been analyzed to determine the magnitude (38·9 Hz) and sign (positive) of ¹J(C? C) relative to those of ³J(H? H) (positive). This type of coupling appears to be rather insensitive to the presence of bromine or methyl as substituents on the carbons.     

13C and 199Hg nuclear magnetic resonance study of alkynyl mercury(II) compounds

Alkynyl mercury compounds of the type Hg(CCR)₂ (I), R′HgCCR (II) and R′HgCCHgR′ (III) have been studied by ¹H, ¹³C and ¹⁹⁹Hg NMR. Chemical shifts (δ¹H, δ¹³C, δ¹⁹⁹Hg) and coupling constants J(¹⁹⁹Hg¹H), J(¹⁹⁹Hg¹³C), J(¹³C¹H) and J(¹³C¹³C) (in natural abundance) are reported. The changes in magnitude of the coupling constants ¹J(¹⁹⁹Hg¹³C) and ¹J(¹³C¹³C) cannot be fully explained in terms of changes in the “s-character” of the HgC bond and the CC bond, respectively. The shielding of the alkynyl carbon linked to mercury in II is decreased by ca. 23 ppm as compared to the analogous carbon in I. This indicates a greatly different degree of polarization for the HgC bonds in I and II in agreement with the behaviour of ¹J(¹⁹⁹Hg¹³C) and ¹J(¹³C¹³C). The solvent and temperature dependence of the ¹⁹⁹Hg chemical shift of I (R = C₆H₅, C₄H₉ⁿ) and II (R = H, R′= CH₃) has been studied. The results indicate covalent interactions of I with amines, pyridine, dimethylsulphide and Br⁻, while the interaction with acetonitrile and oxygen donors (DMSO, DMF, dioxane, acetone) is of a different nature.     

Synthetic,Mechanistic, and Theoretical Studies on the Generation of Iridium Hydride Alkylidene and Iridium Hydride Alkene Isomers

Experimental and theoretical studies on equilibria between iridium hydride alkylidene structures, [(Tp^Me2)Ir(H){?C(CH₂R)ArO }] (Tp^Me2=hydrotris(3,5‐dimethylpyrazolyl)borate; R=H, Me; Ar=substituted C₆H₄ group), and their corresponding hydride olefin isomers, [(Tp^Me2)Ir(H){R(H)C? C(H)OAr}], have been carried out. Compounds of these types are obtained either by reaction of the unsaturated fragment [(Tp^Me2)Ir(C₆H₅)₂] with o‐C₆H₄(OH)CH₂R, or with the substituted anisoles 2,6‐Me₂C₆H₃OMe, 2,4,6‐Me₃C₆H₂OMe, and 4‐Br‐2,6‐Me₂C₆H₂OMe. The reactions with the substituted anisoles require not only multiple C? H bond activation but also cleavage of the Me? OAr bond and the reversible formation of a C? C bond (as revealed by ¹³C labeling studies). Equilibria between the two tautomeric structures of these complexes were achieved by prolonged heating at temperatures between 100 and 140 °C, with interconversion of isomeric complexes requiring inversion of the metal configuration, as well as the expected migratory insertion and hydrogen‐elimination reactions. This proposal is supported by a detailed computational exploration of the mechanism at the quantum mechanics (QM) level in the real system. For all compounds investigated, the equilibria favor the alkylidene structure over the olefinic isomer by a factor of between approximately 1 and 25. Calculations demonstrate that the main reason for this preference is the strong Ir–carbene interactions in the carbene isomers, rather than steric destabilization of the olefinic tautomers.     

The effect of solvent accessible surface on Hammett‐type dependencies of infinite dilution 29Si and 13C NMR shifts in ring substituted silylated phenols dissolved in chloroform and acetone

Infinite dilution ²⁹Si and ¹³C NMR chemical shifts were determined from concentration dependencies of the shifts in dilute chloroform and acetone solutions of para substituted O‐silylated phenols, 4‐R‐C₆H₄‐O‐SiR′₂R″ (R = Me, MeO, H, F, Cl, NMe₂, NH₂, and CF₃), where the silyl part included groups of different sizes: dimethylsilyl (R′ = Me, R″ = H), trimethylsilyl (R′ = R″ = Me), tert‐butyldimethylsilyl (R′ = Me, R″ = CMe₃), and tert‐butyldiphenylsilyl (R′ = C₆H₅, R″ = CMe₃). Dependencies of silicon and C‐1 carbon chemical shifts on Hammett substituent constants are discussed. It is shown that the substituent sensitivity of these chemical shifts is reduced by association with chloroform, the reduction being proportional to the solvent accessible surface of the oxygen atom in the Si‐O‐C link. Copyright © 2012 John Wiley & Sons, Ltd.     

Configurational assignment in alkyl‐branched sugars via the geminal C,H coupling constants

The measurement of the magnitude and sign of ²J(C,H) couplings offers a reliable way to determine the absolute configuration at a carbon center in a fixed cyclic system. A decrease of the dihedral angle ? in the O—C_A—C_B—H fragment always leads to a change of the ²J(C_A,H_B) coupling to more negative values, independent of the type and position of substituents at the two carbon centers. The orientations of the two substituents at C‐3 of the epimeric pair 1 and 2 were determined unambiguously through the measurement of the geminal coupling constants between C‐3 and the hydrogen atoms at C‐2 and C‐4. In particular, ²J(C‐3,H‐2ax) with ?1.5 Hz, ? = 174° in 1 and ?6.6 Hz, ? = 47° in 2 , and ²J(C‐3,H‐4) with +1.5 Hz, ? = 175° in 1 and ?4.7 Hz, ? = 49° in 2 showed the greatest differences between the two epimers. Both couplings therefore allow the determination of the absolute configuration at C‐3. It should be noted, however, that the size of the coupling constants can be different for dihedral angles of nearly identical size, when there are different numbers of electronegative substituents on the two coupling pathways, i.e. no O‐substituent at C‐2, but one axial O‐substituent at C‐4. It becomes clear that it is not sufficient to measure the magnitude of ²J coupling constants only, but that the sign of the geminal coupling is needed to identify the absolute configuration at a chiral center. The coupling of C‐3 with H‐2eq is not useful for the determination of the configuration at C‐3, as the similarity of the dihedral angles ? (O—C‐3—C‐2—H‐2eq) (57° in 1 and 70° in 2 ) leads to identical coupling constants (?6.1 Hz) for both epimers. Copyright © 2003 John Wiley & Sons, Ltd.     

13C NMR: Substituent effects on one-bond 15N?13C coupling constants in anilines and anilinium ions

¹J(¹⁵N¹³C) values obtained from FT ¹³C NMR spectra were measured for a number of ¹⁵N-enriched aniline derivatives and are found to exhibit varying degrees of dependence on the nature of the ring substituent. Theoretical calculations of ¹J(¹⁵N¹³C) values for representative members of the systems examined were made using INDO parameters and a ‘sum-over-states’ perturbation approach. The calculated coupling constants are generally in fair agreement with experimental values when the integral products S_N²(o)S_C²(o) and (r^?3)_N(r^?3)_C have values of 34.437 au^?6 and 2.770 au^?6, respectively.     

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.     

1H- and 13C-NMR Investigations of Heptafulvenes

¹H- and ¹³C-NMR spectra of a series of 8-R¹-substituted as well as of 8,8-R¹, R²-disubstituted heptafulvenes, varying from inversely polarized ( 3l ) to unpolar ( 3h ) and polar heptafulvenes with electron-withdrawing groups ( 3d , e , f ), have been analyzed and compared with those of methoxytropylium salt 5a . The results concerning ³J (H,H) values and ¹³C-chemical shifts are shown in Figs. 5 and 6. It turns out that all the NMR parameters are strongly influenced by substituents R¹, R², but contrary to planar pentafulvenes, no linear correlations of the NMR parameter vs. Hammett substituent constant σ⁺ are obtained in the series 3l → 3d . ³J coupling constants J(2,3)/J(4,5) and J(3,4) are not much influenced by substituent changes in the series 3l → 3h , but are approaching in the row 3h → 3d . Similarly, signals of the ¹³C-atoms undergo a moderate shift to higher frequencies in the row 3l → 3h , but are strongly influenced by ? M groups, whereby the sensitivity is decreasing in the series C(7) > C(2)/C(5) > C(3)/C(4) > C(1)/C(6). These results are essentially explained by a boat conformation of inversely polarized heptafulvenes of the type 3l and an increasing planarization of the ring on going to polar heptafulvenes of type 3d .     

Sélénophènes substitués. Additivité de l'influence des substituants sur les couplages J(H?H) et J(Se?H)

The spin-spin coupling constants J(H? H) and J(Se? H) of 2- and 3-substituted selenophenes, whose signs have been obtained by double resonance experiments, have been correlated with the reactivity constants F and R of Swain and Lupton by means of linear equations J = i + fF + rR. The relative inductive and mesomeric contributions to the coupling constants are discussed. Substituent effects on J(H? H) and J(Se? H) are found to be additive in 2,4-disubstituted selenophenes. In agreement with experimental results, this additivity relationship indicates that ³J(Se? H) becomes negative in 2,4-dinitroselenophene. Evidence is given from long range coupling constant data that 2-formylselenophene exists almost exclusively in the Se? O cis conformation and 3-formylselenophene in the Se? O trans conformation.     

Etude par Résonance Magnétique Nucléaire du carbone 13 de complexes du cobalt (III) et de la diméthylglyoxime

From a carbon magnetic resonance study of several alkylcobaloximes RCo(DMG)₂B (DMG = dimethylglyoximate monoanion), it was possible to estimate the α, β and γ effects of the Co(DMG)₂B group on the chemical shifts of the carbon atoms of various alkyl groups R. The chemical shifts of the carbon atoms belonging to the equatorial ligands and to the axial base B are not significantly affected by structural modification of the R groups. Values of δ in benzylcobaloximes XC₆H₄CH₂Co(DMG)₂B agree with a donor effect of the ? CH₂Co(DMG)₂B radical. Values of ¹J(¹³C? H) coupling constants, measured in ¹³C enriched methylcobaloximes, do not vary appreciably when B is changed (J(¹³C? H) = 137 ± 1 Hz) and are close to the value obtained for methylcobalamine.