1H-and 13C-NMR Investigation of Pentafulvenes

¹H- and ¹³C-NMR spectra of a series of 6-(p-X-phenyl)pentafulvenes 1 – 9 as well as of 6-R-substituted and 6,6-R¹,R²-disubstituted pentafulvenes 10 – 23 have been analysed. It turns out that the π-system of pentafulvenes is an attractive probe for the investigation of electronic substituent effects. Changes of vicinal H,H-coupling constants with increasing electron-donating capacity of the substituents X and R are interpreted in terms of an increasing π delocalisation in the 5-membered ring, and linear correlations of Hammett Substituent constants σ or MNDO-calculated C–C bond lengths and ³J values are observed. On the other hand, a systematic high-field shift of ₁₃C chemical shifts of the ring C-atoms is induced by electron-releasing substituents R and X, which decreases in the series C(5) > C(2)/C(3) > C(1)/C(4), and which mainly reflects changes in π-charge density.     

Conformational Analysis of the cis- and trans-Isomers of FK506 by NMR and Molecular Dynamics

The potent immunosuppressant drug FK506 ( 2 ) has been examined by ¹H- and ¹³C-NMR spectroscopy and NOE-restrained molecular dynamics to elucidate the conformation in solution. A combination of two- and three-dimensional NMR techniques was used to completely assign the ¹H- and ¹³C-NMR chemical shifts of the two configurational isomers resulting from the cis-trans isomerization about the single amide bond. Hetero- and homonuclear coupling constants were measured to assign the diastereotopic methylene protons at C(16), C(18), and C(23). Intramolecular H? H distances were defined from NOESY spectra recorded at ?30° in CDCl₃ and used as constraints in molecular-dynamics simulations. The conformational preferences of 2 in solution are discussed in light of the constitutional features recently proposed to be necessary for binding and activity.     

Fulvene,VII. Analyse der 13C- und 1H-NMR.-Spektren

Carbon-13 and proton NMR. spectra of pentafulvene and of a series of 6-substituted fulvenes have been analysed and assigned by homo- and heteronuclear double resonance and with the aid of iterative computation. ¹³C and ¹H chemical shifts are interpreted in terms of substituent effects and compared with π-electron charges calculated for the unsubstituted fulvene. From ¹³C shifts a 10 percent contribution of dipolar structures to the electronic configuration of fulvene may be estimated. All long-range proton-proton coupling constants including relative signs and some proton-carbon couplings in the fulvene spin system have been determined and assigned.     

The use of one-bond,heteronuclear coupling constants (1J —C,H) as structure reporters in 13 C-N.M.R. of oligosaccharides containing 3-deoxy-(=D)-manno-2-octulosonic acid

In proton-coupled, ¹³ C-n.m.r.-spectra of 3-deoxy-(=D)-$\text{manno}$-2-octulopyranosylono (KDO$\text{p}$-)derivatives, the ¹$\text{J}$-C-5,H-5 is significantly larger (148 Hz) than the respective coupling constants of the other carbon signals, and the chemical shift of the signal displaying this spacing indicates whether position 5 is glycosidated or unsubstituted.     

Strukturbestimmung von O-Methylazafrinmethylester durch 13C-NMR.-Spektroskopie

Structure Determination of Azafrin Methyl Ester 5-O-Monomethyl Ether by ¹³C-NMR.-Specta. The structure of the monomethyl ether ( 2 ) of azafrin methyl ester ( 1 ) was determined by a partial analysis of the ¹³C-NMR.-spectra. Assignments of quaternary carbon atoms and methyl groups in the cyclohexane ring were achieved using vicinal ¹³C-, ¹H-spin coupling. Substituent effects on methyl and methylene carbon atoms in 2 are discussed with respect to the conformation of the methoxy group. The spectra prove C(5)? OH as the site of methylation. Therefore C(5)? OH is less hindered than C(6)? OH.     

Proton-coupled 13C NMR and {14N}—1H-INDOR of highly-substituted 6-membered heterocycles. I—trisubstituted pyridones and isomeric aminopyrones; tetrasubstituted pyridines

The structural elucidation by NMR spectroscopy of trisubstituted α-pyridones and the isomeric 2-amino-γ-pyrones as well as their internal and external pyrylium salts is described. The most useful parameter for the differentiation between α-pyridones and isomeric γ-pyrones is the geminal coupling constant ²J(C-6, H-5) which changes from ～2.5 Hz to ～7 Hz whenever the cyclic amide group is replaced by an oxa-function; this applies to both the γ-pyrones and their pyrylium salts. The value of J(C-6, H-5) in the pyridones resembles that of the analogous coupling in N-vinylacetamide, whose sign determination by the selective population inversion (SPI) technique is reported. The ¹³C chemical shifts of seven pyridones, pyrones and pyrylium salts are reported and their structural correlations are discussed. Quick structural assignments in these classes of compounds may also be performed by evaluating the ¹⁴N chemical shifts, which often are accessible by the {¹⁴N}—¹H-INDOR technique. The proton coupled ¹³C NMR spectra of two tetrasubstituted pyridines are also reported, and empirical correlations between long range C? H coupling constants and substituent electronegativity are discussed.     

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.     

Über Pterinchemie 51. Mitteilung [1] CNDO-Rechnungen an Pterin, 6,7-Dimethyl-7,8-dihydropterin und 5-Formyl-6, 7-dimethyl-5,6,7,8-tetrahydropterin

The ¹³C-NMR.-spectra of 7,8-dihydropterines and 5,6,7,8-tetrahydropterines show a large difference in the chemical shifts of the 4a- and 8a-sp²-carbon atoms. From the CNDO calculations it is apparent that there is a considerable difference in electron density at C(4a) and C(8a) atoms, which leads to a strong polarity of the C? C-Bond. The electron distribution in the highest occupied molecular orbital (HOMO) is discussed.     

NMR-Untersuchungen an Dicyclopentadienderivaten. IV—1-Syn/anti-Epimere von endo-Dicyclopentadienderivaten

The syn/anti-arrangement of some substituents R in position 1 of endo-dicyclopentadiene derivatives is investigated by ¹H-and ¹³C n.m.r. spectroscopy. The HH-coupling constants of the epimeric alcohols 2 and 3 are determined by paramagnetic shift experiments [Eu(fod)₃] and the observed relative paramagnetic shifts ΔEu used for the determination of the configuration. The increasing steric compression in the syn-epimers is well reflected by the ¹H- and ¹³C n.m.r. chemical shifts.     

1H- and 13C-NMR. Studies of some metal complexes of o,o′-dihydroxyazobenzenes

The aromatic ¹H- and ¹³C-NMR. spectra of some metal complexes of o, o′-dihydroxyazobenzenes are shown to be useful in distinguishing the two possible isomers (acolar and discolar) stemming from the non equivalence of the two ligating azo nitrogen atoms. The ortho aromatic carbon atoms, C(6) and C(12) experience relatively large upfield shifts between 12.8 and 15.7 ppm when the adjacent nitrogen atom is coordinated. The protons attached to these carbon atoms are shifted downfield. The values ⁿJ (¹⁵N, ¹³C) for the ligand 2,2′-dihydroxy-3-methyl-4′-chloro-5-(t-butyl)-¹⁵N-azobenzene are reported.     

Chemistry of the phenoxathiins and isosterically related heterocycles. IX.N-oxidation on the 13C-nmr chemical shifts and coupling constants of the 1-azaphenoxathiin system

The synthesis of 1-azaphenoxathiin N-oxide is described. Total assignment of the ¹³C-nmr spectrum and the effects of the N-oxide moiety on the chemical shifts and ¹H-¹³C spin couplings constants are described and compared to the parent 1-azaphenoxathiin system. The potential for the use of N-oxidation induced changes in ¹³C-nmr chemical shifts and ¹H-¹³C coupling constants as an assignment criterion is also discussed.     

1H- and 13C-NMR Investigation of Nonafulvenes

¹H- and ¹³C-NMR spectra of a series of nonafulvenes 1 have been investigated. Most nonafulvenes are olefinic molecules with alternating bond lengths, their nine-membered ring deviating strongly from planarity. The 10-monosubstituted nonafulvenes contain 2 sterically different ring segments with a nearly planar (E)-diene system consisting of C(7), C(8), C(9), C(10), and R. Substituents R are influencing C(9) > C(7) > C(5). In symmetrically substituted nonafulvenes a fast process equilibrating olefinic conformers is operating so that pairs of ring protons and ring C-atoms are equivalent and only average substituent effects are observed for C(9) > C(7,2). ¹H- and ¹³C-NMR chemical shifts are not significantly influenced by changes of solvent or temperature. On the other hand, new ¹³C- and ¹H-NMR experiments completing previous investigations by Hafner and Tappe confirm that NMR spectra of 10,10-bis (dialkylamino)nonafulvenes are strongly dependent on solvent polarity and temperature. At ambient temperature and in unpolar solvents, nonplanar conformers are predominant, their spectral data fitting into the series of other nonafulvenes. At low temperature and/or in polar solvents, dipolar conformers are favoured which are characterised by charge separation and a planarised (but not necessarily completely planar) nine-membered ring with negative excess charge. The spectroscopic behaviour of nonafulvenes is reasonably explained by a qualitative scheme (Fig. 7) which is based on a model proposed by Boche for nonafulvenolates.     

15N-, 1H-, and 13C-NMR chemical shifts and electronic properties of aromatic diamines and dianhydrides

We measured the ¹⁵N-, ¹H-, and ¹³C-NMR chemical shifts for a series of aromatic diamines and aromatic tetracarboxylic dianhydrides dissolved in DMSO-d₆, and discuss the relationships between these chemical shifts and the rate constants of acylation (k) as well as such electronic-property-related parameters such as ionization potential (IP), electronic affinity (EA), and the energy ε of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The ¹⁵N chemical shifts of the amino group of diamines (δ_N) depend monotonically on the logarithm of k (log k) and on IP. We inferred the reactivities of diamines whose acylation rates have not been measured from their δ_N, and we propose an arrangement of diamines in the order of their reactivity. The ¹H chemical shift of amino hydrogens (δ_H) and the ¹³C chemical shift of carbons bonded to nitrogen (δ_C) are roughly proportional to δ_N, but these shifts are not as closely correlated with log k and IP. Although the ¹³C chemical shifts of the carbonyl carbon of dianhydrides (δ_C,) varies much less than the δ_C and δ_N of diamines, δ_C, can be an index of acylation reactivity for dianhydrides because it is closely correlated with ε_LUMO. These facts indicate that the chemical shifts of diamines and dianhydrides are displaced according to their electron-donor and electron-acceptor properties, and that these chemical shifts can be used as indices of the electronic properties of monomers. Changes in reactivity caused by the introduction of trifluoromethyl groups into diamines and dianhydrides are inferred from the displacements of δ_N and δ_C © 1992 John Wiley & Sons, Inc.     

Multinuclear NMR Studies of the Substitlent Effects in N-Phenyl-P,P,P-Triarylphospha-λ5-Azenes,Triaryl-Phosphines and Triarylphosphine Oxides

Abstract

A series of N-phenyl-P,P,P-triarylphospha-λ⁵-azenes (1) as well as their ^l5N labeled analogs was synthesized. The ¹³C, ³¹P, and ¹⁵N NMR spectra of this series and those of two other series of related compounds, namely triarylphosphines (2) and triarylphosphine oxides (3), were measured and are reported. Many satisfactory correlations using the mono-substituent parameter (MSP) and the Taft dual-substituent parameter (DSP) treatments with the ¹³C substituent chemical shifts (SCS), ³¹P SCS, ¹⁵N SCS and the one bond P-N, P-C and C-N coupling constants were observed and will be discussed. Thus, for example, the ³¹P and ¹⁵N chemical shifts in 1 correlated with [sgrave]^?with negative slopes while the ³¹P chemical shifts in 3 correlated with those in 1 with a slope of 2.0. The ¹³C chemical shifts in 1 correlated excellently with the corresponding ones in 3 with slopes very close to unity. The substituent effects on the chemical shifts of the various nuclei were shown to be mainly due to changes in the charge distribution on those nuclei. In 1 the one bond P-N and P-C coupling constants correlated with [sgrave]_p and [sgrave]_R respectively. The one bond P-C coupling constants of 1 correlated quite well with those of 3 with a slope of 0.93 while the corresponding correlation of 1 with 2 was quite poor. Taft DSP treatment of ¹J_PCin 1 and 3 were quite similar, ρI and ρR were both negative and ρR was much larger than ρI. Series 2 showed behavior which was different from that shown by 1 and 3 but similar to that shown by other systems with a lone electron pair on the atom bound to the phenyl ring. The substituent effects on the one bond P-N, P-C and C-N coupling constants will be discussed in terms of bonding and hybridization changes between the directly bonded nuclei.     

Heteronuklear überbrückte tricyclische Systeme. Oxa-brexane- und -brendane

Unsaturated cyclic and bicyclic hydrocarbons react with chloral in presence of aluminium chloride to yield tricyclic oxabrexanes which undergo acid catalyzed rearrangements to oxabrendanes. 1,5-cyclooctadiene gives the new oxa-cyclo[c, d]octahydropentalen. Structural evaluations and stereochemical assignments are discussed on the basis of detailed ¹H- and ¹³C-NMR.-spectra.     

13C n.m.r. spectra of 2-substituted pyrimidines

¹³C n.m.r. chemical shifts and carbon-proton coupling constants of 2-substituted pyrimidines are reported. The carbon chemical shifts are correlated with π-electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH₂, OCH₃ and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon-proton coupling constants do not correlate with the electronegativity of the substituents. Carbon-proton coupling constants and proton-proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon-proton coupling constants in 2(1H)-pyrimidinone and 2(1H)-pyrimidinethione which accompany anion and cation formation are reported.     

Polymerization of coordinated monomers. VI. Molecular complex formation of methyl methacrylate coordinated to stannic chloride with styrene or toluene

The equilibrium constants for the complex formation between stannic chloride and methyl methacrylate were determined in n-hexane–toluene solution at 0, ?20, and ?30°C by using the absorption band at 350 nm. Continuous variation plots at ?20°C in n-hexane based on the ¹H-chemical shifts definitely show a 1:1 interaction between the coordinated methyl methacrylate and styrene or toluene. The magnitudes of the shifts for the four groups of protons in methyl methacrylate are found to be in a specific ratio in common with the 1:2 complex–styrene or -toluene system. The equilibrium constants for the ternary molecular complex formation between the 1:2 complex and styrene or toluene were determined in n-hexane in the temperature range ?50 to +20°C by use of the chemical shifts. The concentrations of the complex species in the alternating copolymerization solutions were estimated by use of the equilibrium constants. There is a linear relationship between the enthalpy and the entropy changes for the ternary molecular complex formation, which is governed by the enthalpy factor. The specificity of the interactions indicates a specific time-averaged orientation of benzene ring to the coordinated methyl methacrylate. The effects of the coordination of methyl methacrylate to stannic chloride were discussed on the basis of results of ¹³C-NMR spectroscopy.     

NMR studies of bridged ring systems: XIX—13C?1H spin coupling and 13C chemical shift of the bridge methylene in benzonorbornene and benzonorbornadiene

Data on ¹³C chemical shifts and ¹³C? ¹H spin coupling constants of norbornane ( 1 ), norbornene ( 2 ), norbornadiene ( 3 ), benzonorbornene ( 4 ) and benzonorbornadiene ( 6 ) are reported. The non-equivalence in J(¹³C? H) values determined from the two bridge methylene proton signals in 2,2,3,3-tetradeuteriobenzonorbornene ( 5 ) and 6 is briefly discussed. The extraordinary deshielding of the bridge methylene carbon in 6 has been noted.     

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 .     

Low-Temperature 13C-NMR Spectra of 6Li- and 13C-Labelled Sulfur- and Selenium-Substituted Organolithium Derivatives

The ¹³C-NMR spectra of 19 different, singly, doubly, and triple ¹³C-labelled α-sulfur- and α-selenium-substituted ⁶Li-derivatives generated from methyl and phenyl thioethers, thioacetals, trithio-orthoesters and from their selenium analogues have been recorded in ethereal solutions (tetrahydrofuran (THF), 2-methyltetrahydrofuran (MTHF) at temperatures between ?30° and ?110°. The effects of H/Li-exchange upon chemical shifts and coupling constants, as well as the values and multiplicities of Li, ¹³C-coupling are interpreted in vie wof crystal structures of some of the same compounds. In two thirds of the cases studied, the H-decoupled ¹³C-NMR signals observed below ?80° were triplets, proving that the C-atoms are bonded to single ⁶Li-atoms. This is compatible either with monomeric or with dimeric, heteroatom-bridged structures. The direct ¹H, ¹³C- and ¹³C, ¹³C-coupling constants (¹J) decrease, the ¹³C, ⁷⁷Se-coupling constants increase upon lithiation. More striking is that the geminal coupling ¹³C-S-¹³C (²J) is too small to be observed in the non-metalated species, while it ranges from 3.7 to 7.5 Hz in the lithiated derivatives. These observations may be interpreted as resulting from delocalization of electron density from the carbonionic center towards the adjacent heteroatom.