13C NMR spectra of diazastilbenes. I—trans-styryldiazines

The ¹³C NMR spectra of all trans-styryldiazines, methyldiazines and trans-styrylpyridines have been fully assigned. Empirical shift increments were obtained for the chemical shifts of the carbon atoms; these are discussed in the light of theoretical considerations.     

13C NMR spectroscopy of cyclopropane derivatives. 1—monocyclic compounds

The ¹³C NMR data of an appreciable number of cyclopropane derivatives have been collected. Most of the spectra were recorded by ourselvesand some were taken from the Literature. With a view to furthering the useof ¹³C NMR spectroscopy as a diagnostic tool in this field, we havemeasured not only the chemical shifts,δ, but also the coupling constants ¹J(CH). It is shown that both embody valuable structural information.     

An NMR study of 2-alkoxy-1,3,2-dioxaphospholanes. I—13C chemical shifts

Measurements of the ¹³C chemical shifts of 2-alkoxy-1,3,2-dioxaphospholanes have allowed the determination of the contribution of the substituent to the α-, β- and γ-carbon chemical shifts of attached alkyl groups. The preliminary assignments of the signals were made using the following information; relative intensities, variations in coupling constants J(³¹P¹³C) and the existence of linear correlations between the shifts of carbon atoms in the P-alkoxy groups and the degree of substitution of the observed carbon or of its neighbours.     

1H and 13C NMR spectral assignment of androstane derivatives

(1)H and (13)C NMR spectroscopic data for 5alpha-androstanes and halo-5alpha-androstanes with different substituents at positions C-3, C-9, C-11 and C-17 were examined and assigned by a combination of 1D and 2D NMR experiments. The substituent effects on the (13)C chemical shifts were compared with those of epi-androsterone, used as a reference compound. The coupling constants (n)J((19)F,(13)C) were measured for compounds 6, 8, 11 and 14.     

Carbon-13 NMR studies of substituted naphthalenes. I—complete assignments of the 13C chemical shifts with the aid of deuterated derivatives

Proton-coupled as well as noise-decoupled ¹³C NMR spectra of several substituted naphthalenes have been studied. Complete assignments of the ¹³C signals based on selectively deuterated derivatives and on the ¹³C? ¹H coupling pattern have been made. For the methoxynaphthalenes, acetylnaphthalenes and naphthaldehydes the dominant conformations of the substituents have been deduced from the ¹³C chemical shifts.     

A joint theoretical and experimental investigation on the 13C and 1H NMR chemical shifts of coumarin derivatives

¹H and ¹³C NMR chemical shifts of coumarin derivatives have been determined using first principles approaches with and without accounting for the effects of the solvent and compared to experiment in order to assess their reliability. Good linear relationships are obtained between theory and experiment, which allows correcting the calculated values for systematic errors. This is particularly the case when using the PCM scheme to model the solvent effects because the δ values larger than 150 ppm are more difficult to reproduce. The final accuracy of the method amounts to about 1 ppm for ¹³C and 0.05 ppm for ¹H.     

13C NMR study of N-unsubstituted aziridines: I—steric effects,pseudoconjugation

¹³C chemical shifts for twenty-nine alkyl and phenyl substituted N-unsubstituted aziridines have been measured. Additivity parameters for methyl, phenyl and aziridyl carbons have been derived with the aim of testing the consistency of the assignments made on the basis of chemical shift considerations and off-resonance decoupling information. The observed chemical shifts are discussed in terms of steric and pseudoconjugation effects.     

1H and 13C NMR study of dihydro derivatives of methylphenobarbital

Sodium borohydride reduction of methylphenobarbital leads to the formation of two different dihydroderivatives, reduced either in position 4 or position 6. The structures of the derivatives have been determined through analysis of the ¹H and ¹³C NMR spectra of phenobarbital, methylphenobarbital and their derivatives. Detailed interpretation of the spectra and the resulting spectral parameters indicate conformations where the hydroxyl groups are axial and trans to the ethyl group. In these configurations the phenyl ring becomes equatorial. The results also allow an unambiguous assignment of the resonances of the phenyl carbons 2′(6′) and 3′(5′) of phenobarbital and the carbonyl carbons 4 and 6 of methylphenobarbital, differing interpretations having been previously advanced in the literature.     

13C and 1H NMR investigation of the structure of N″-sulphonyl-N-alkylideneformamidrazones

The ¹³C and ¹H NMR spectra of N″-sulphonyl-N-alkylideneformamidrazones have been recorded and the chemical shifts assigned. The tautomeric structure proved to be an N²- alkylidenehydrazide sulphonylimide. The barrier to rotation around the CN¹ bond was estimated from variable from temperature ¹H NMR measurements, and the Z/E ratio and its solvent dependence was investigated.     

Complete assignment of 1H and 13C NMR data of pravastatin derivatives

The complete ¹H and ¹³C NMR data of 27 pravastatin derivatives are presented. Assignment was achieved by use of 1D and 2D NMR experiments (selective 1D NOE, COSY, NOESY, HSQC, HMBC). Copyright © 2008 John Wiley & Sons, Ltd.     

A NMR investigation of proline and its derivatives. II—Conformational implications of the 1H NMR spectrum of L-proline at different pH

The 250 MHz ¹H NMR spectrum of L -proline is comprehensively analysed by computer simulation for different pH values. A fast endo–exo interconversion has already been proposed from chemical shift and coupling constant data. A critical comparison of the vicinal coupling constants leads to the conclusion that in basic solution the equilibrium is shifted towards a more endo conformation. The position of the carboxylic plane in the ring space is given by the relative intramolecular chemical shift of the geminal protons and by the typical patterns of the H_α multiplet. These results are applied to the analysis of the spectra of Pro? NH₂ and Ac? Pro? NH₂.     

29Si and 13C NMR studies of organosilicon chemistry. V—Sugar derivatives

²⁹Si spectra have been obtained for four trimethylsilylated hexopyranoside sugars, and the resonance due to the CH₂OSiMe₃ group at position 5 has been assigned by experiments involving gated decoupling at a single ¹H frequency.     

1H, 13C and 15N NMR assignments of phenazopyridine derivatives

Phenazopyridine hydrochloride (1), a drug in clinical use for many decades, and some derivatives were studied by one- and two-dimensional (1)H, (13)C and (15)N NMR methodology. The assignments, combined with DFT calculations, reveal that the preferred protonation site of the drug is the pyridine ring nitrogen atom. The chemoselective acetylation of phenazopyridine (2) and its influence on the polarization of the azo nitrogen atoms were evidenced by the (15)N NMR spectra. Molecular calculations of the phenazopyridines 2-4 show that the pyridine and phenyl groups are oriented in an antiperiplanar conformation with intramolecular hydrogen bonding between the N-b atom and the C-2 amino group preserving the E-azo stereochemistry.     

1H and 13C NMR spectral assignments of isoquinuclidine-3,5-dione derivatives

The 1H and 13C NMR spectra of six 5-substituted 2-azabicyclo[2.2.2]octane derivatives were fully assigned by COSY and HSQC experiments.     

Complete 1H and 13C NMR spectral assignment of hydrogenated oxoisoaporphine derivatives

2,3,8,9,10,11‐Hexahydro‐7H‐dibenzo[de,h]quinolin‐7‐one, 5‐methoxy‐2,3,8,9,10,11‐hexahydro‐7H‐dibenzo[de,h]quinolin‐7‐one, 5‐methoxy‐6‐hydroxy‐1,2,3,7a,8,9,10,11,11a,11b‐decahydro‐7H‐dibenzo[de,h]quinolin‐7‐one, 5‐methoxy‐5,6,8,9,10,11‐hexahydro‐4H‐dibenzo[de,h]quinolin‐7‐ol, 5,6,8,9,10,11‐hexahydro‐4H‐dibenzo[de,h]quinolin‐7‐ol and 5,6‐dihydro‐4H‐dibenzo[de,h]quinolin‐7‐ol were prepared by catalytic hydrogenation of oxoisoaporphines or their 2,3‐dihydro derivatives over PtO₂ in acetic acid under mild conditions. Their structures were confirmed and ¹H and ¹³C NMR spectra were completely assigned using a combination of one‐ and two‐dimensional NMR techniques. Copyright © 2003 John Wiley & Sons, Ltd.