Studies in tertiary amine oxides. Part V—carbon-13 nuclear magnetic resonance spectra of some N-aryl tertiary amines,the corresponding N-oxides and the meisenheimer rearrangement products

The carbon-13 NMR spectra of some N-(2- or 4-nitrophenyl) tertiary amines and their corresponding N-oxides have been analysed. These N-oxides undergo thermal rearrangement to O-arylhydroxylamines, for which the ¹³C NMR spectral assignments were also carried out. The N-oxidation effect on the aromatic and aliphatic fragments is calculated.     

Studies in tertiary amine oxides. III—carbon-13 NMR assignment of N-alkynyl cyclic amines

Carbon-13 NMR spectra of 24 N-alkynyl cyclic amines were analysed. The effect of substituting the acetylenic proton by n-butyl, tert-butyl and phenyl groups was determined.     

Carbon-13 NMR study of some acetylenic amines,the N-oxides and their rearrangement products

Carbon-13 NMR chemical shifts of some N, N-dialkyl-4-acetoxybut-2-ynylamines and their corresponding N-oxides have been analysed. These N-oxides undergo thermal rearrangement to O-allenyl hydroxylamine for which the ¹³C NMR spectral assignments were also carried out. The effect of N-oxidation on the chemical shifts is calculated.     

Carbon-13 nuclear magnetic resonance spectra: III—2-heteroadamantanes

The ¹³C n.m.r. spectra of some 2-heteroadamantanes and 1-substituted 2-heteroadamantanes are reported. The influences of the heteroatoms in the adamantane framework, and those of the substituents attached to it, on the ¹³C chemical shifts of the adamantane carbons are investigated and compared with related compounds such as the corresponding heterocyclohexane derivatives and 2-mono- and 2,2-disubstituted adamantanes. The nonadditivity of the substituent effects for 1-substituted 2-heteroadamantanes, especially for the geminally substituted carbons, is substantially confirmed. In addition, the influences of a missing CH₂ group and of NCH₃ carbons upon the ¹³C chemical shifts of the carbons in the adamantane system are described.     

Solvent effects in nuclear magnetic resonance spectra of some pyrazines,pyrimidines and their N-oxides

The benzene-induced solvent effects upon the proton chemical shifts of various pyrazines, pyrimidines and their N-oxides are described. Larger chemical shift effects, implying closer benzeneheterocycle association, are noted in the N-oxides as compared to the non-oxidized heterocycles. The solvent-induced chemical shift changes can be used to establish the site of N-oxidation in those instances where different isomers can be formed.     

The carbon-13 nuclear magnetic resonance spectra of anthraquinone,eight polyhydroxyanthraquinones and eight polymethoxyanthraquinones

The ¹³C NMR spectra of anthraquinone, eight hydroxyanthraquinones and eight methoxyanthraquinones are reported. Peak assignment for the carbon atoms of these compounds is achieved by using decoupling techniques and by intercomparison of the variously-substituted derivatives. Carbonyl chemical shifts in the hydroxyanthraquinones can be rationalized in terms of cross conjugation and intramolecular hydrogen bonding and in terms of cross conjugation in the methoxyanthraquinones. Hydroxy and methoxy substituent chemical shifts are also reported.     

Carbon-13 nuclear magnetic resonance spectra. I—Monosubstituted adamantanes and adamantanones

The chemical shifts of 4_ax and 4_eq substituted adamantanones are compared with those calculated with the aid of a given additivity rule. It is found that both δ carbons are shielded with respect to the substituent. In contract to the situation for the y-atoms, however, the δ_syn atom is less shielded than the δ_anti atom. In most cases the additivity rule predicts the chemical shifts with an accuracy of approximately 1 ppm. Exceptions are carbon atoms 4 and 9 of the 4_eq substituted adamantanones. In both cases the measured values are 4 to 6 ppm upfield. This can possibly be explained by an electronic interaction between the carbonyl group and the substituent.     

Carbon-13 nuclear magnetic resonance studies of anthraquinones Part II—hydroxymethoxyanthraquinones,acetoxymethoxyanthraquinones and naturally occuring anthraquinone analogues

The ¹³C NMR spectra of hydroxymethoxyanthraquinones, acetoxymethoxyanthraquinones and naturally occuring anthraquinone derivatives are reported and all chemical shifts assigned. Hydroxy, methoxy and acetoxy substitution parameters are additive except in the case of 1,2-disubstitution and for 1-hydroxyanthraquinones substituted on C-3 or on C-4 by an hydroxy or a methoxy group. In anthraquinones substituted on C-2, carbon shieldings are found to be sensitive to steric interference and to conjugative electron release by the 1-OCH₃.     

Oxygen-17 and carbon-13 nuclear magnetic resonance spectra of thiophene- and pyrrole-2-carboxaldehyde condensation products prepared from ephedrine derivatives

Natural abundance ¹⁷O nmr (acquired in acetonitrile at 70°) and ¹³C nmr (acquired in deuteriochloroform at 37°) spectroscopic data for four oxazolidines and related imino alcohols are reported: relationships of chemical shifts and ¹⁷O line widths at half-heights to structures are discussed.     

Carbon-13 nuclear magnetic resonance spectra of isomeric oxaziridines. Effects of the nitrogen lone pair on carbon-13 chemical shifts

The carbon-13 n.m.r. spectra of several oxaziridines were measured. Aliphatic and aromatic ipso carbon atoms trans to the lone pair of nitrogen in oxaziridines were shifted upfield by c. 9 ppm, and 3.4 ppm, respectively, in comparison with isomers of inverted configuration. The results suggest that the nitrogen lone pair is partially responsible for the observed upfield shifts.     

Carbon-13 nuclear magnetic resonance of the azomethine group. II—(II.II) conjugation and twist angles

Torsional angles in some mono-substituted conjugated benzenes were determined from the chemical shift of the para carbons. Similar results were obtained from ketones and imines, and the torsional angles increase, as expected, with steric hindrance. It is possible to assign a syn or anti stereochemistry for the imines from the value of the torsional angle.     

Deuterium nuclear magnetic resonance spectroscopy. II—distribution of deuterium in some labelled nitrogen heterocyclic compounds

Pyridine, methylpyridines, quinoline and isoquinoline have been labelled with deuterium using pre-reduced platinum dioxide (PtO₂·2H₂O) and heavy water. Their ²H chemical shifts from monodeuteriated TMS have been assigned. The extent of the labelling has been determined directly by ²H NMR spectroscopy.     

Studies on tertiary amine oxides. LXVII . Reactions of aromatic N-oxides with 3-arylrhodanines in the presence of acetic anhydride

Quinoline 1-oxides 1 readily react with 3-arylrhodanines 2 in the presence of acetic anhydride to afford 3-aryl-5-(2-quinolyl)rhodanines 3 in high yields. These products resist hydrolysis under both alkaline and acidic conditions, but is oxidized to quinaldinic acid 1-oxide 4 with 30% hydrogen peroxide in hot acetic acid. Besides isoquinoline 2-oxide 5 , pyridine 1-oxide 7a also reacts in the same way to give 3-aryl-5-(2-pyridyl)rhodanines 8 , although the reactivity of γ-picoline 1-oxide 7b is considerably lower. Contrary to 3 , 3-phenyl-5-(2-pyridyl)rhodanine 8a is successfully hydrolyzed with boiling 48% hydrobromic acid to 2-pyridinemethanethiol 10 in 57% yield.     

Barriers to internal rotation in 1,3,5-trineopentylbenzenes: V—conformational studies by carbon-13 magnetic resonance

The temperature dependence of the carbon-13 NMR signals in three completely substituted 1,3,5-trineopentylbenzenes has been studied by the Fourier transform technique. The assignment of all peaks was based on studies of 1,3,5-trineopentylbenzene and some of its mono- and disubstituted derivatives. Nearly all carbon signals showed a splitting into several peaks at low temperature, which gave information about the existing rotamers in the completely substituted compounds. Spectra for one compound were studied in a narrow temperature interval in order to test the reliability of rate constants obtained from ¹³C FT spectra. Good agreement was found between previously reported values obtained from ¹H NMR and those obtained in this investigation.     

Saturated amine oxides: part 10. hydroacridines: part 32. linear 17O/13C and 13C/13C chemical shift correlations between saturated azaheterocyclic N‐methylamine N‐oxides,and the methiodides of their parent amines

Two kinds of good linear correlations were found between the chemical shifts of saturated six‐membered azaheterocyclic N‐methylamine N‐oxides and the chemical shifts of the methiodides of their parent amines. One of the correlations occurs between the ¹⁷O chemical shift of the N⁺―O^– oxygen in the N‐oxides and the ¹³C chemical shift of the N⁺―CH₃ methyl group analogously situated in the appropriate methiodide (r = 0.9778). This correlation enables unambiguous configuration assignment of the N⁺―O^– bond, even if the experimentally observed ¹⁷O chemical shift of only one N‐epimer is available, provided the ¹³C chemical shifts of both N⁺―CH₃ groups in the methiodide are known and assigned; furthermore, it can be used also for the estimation of ¹⁷O chemical shifts of the N⁺―O^– oxygens in N‐epimeric pairs of N‐oxides, for which observed ¹⁷O data hardly become available. The second correlation is observed between the ¹³C chemical shift of the N⁺―CH₃ methyl group in the N‐oxides and the ¹³C chemical shift of the N⁺―CH₃ methyl group analogously situated in the appropriate methiodide (r = 0.9785). It can be used for safe configuration assignment of the N⁺―CH₃ group and, indirectly, also of the N⁺―O^– bond in an amine N‐oxide, even if no ¹⁷O NMR data, and the ¹³C chemical shift of only one N‐epimer is available. Copyright © 2015 John Wiley & Sons, Ltd.     

13C nuclear magnetic resonance studies of saturated heterocycles: II—substituent effects on the 13C chemical shifts of methyl substituted 1,3-dithianes and their application to the determination of conformational equilibria

The ¹³C chemical shifts for 1,3-dithiane and 9 methyl substituted derivatives are reported. Only three of the methyl-1,3-dithianes were conformationally anancomeric and hence the conformational equilibria must be taken into account when deriving the values of the different substituent effects on the ¹³C chemical shifts. The best fit for each substituent effect was obtained when –ΔG^θ (5a-Me) for 5-methyl-1,3-dithiane was given the value 3.8 ± 0.3 kJ mol^?1 and when the difference between –ΔG^θ (2a-Me) and –ΔG^θ (5a-Me) for cis-2,5-dimethyl 1,3-dithiane equalled 3.4 ± 0.4 kJ mol^?1. The conformer populations chosen from our earlier paper¹ were then suitable for all the other conformational equilibria in question. The magnitude of the derived substituent effects are compared with those for cyclohexane and 1,3-dioxane.     

Spectra–structure relationships in carbon-13 nuclear magnetic resonance spectroscopy. Results from a large data base

A link between a substructure searching system and a ¹³C NMR data base has been established and permits the retrieval and examination of the chemical shifts associated with specific substructures. The means by which these searches are accomplished is described and the results from the searches are presented and discussed. The system is interactive, and can be used to locate in the data base the chemical shifts of carbon atoms in precisely defined environments. Alternatively, it may be used to learn the range of the chemical shifts possessed by particular types of carbon atoms, such as N-methyl or O-methyl carbons.     

Monomer distributions and number-average sequence lengths in hydrogenated butadiene–styrene copolymers from carbon-13 nuclear magnetic resonance

Monomer distributions and number-average sequence lengths are determined from ¹³C nuclear magnetic resonance (NMR) data for 1,4- and 1,2-butadiene additions and styrene additions in a series of four hydrogenated butadiene–styrene copolymers. The monomer distribution is expressed in terms of the six unique days from which it is possible to calculate the number-average sequence length of each monomer type. Carbon-13 NMR spectral assignments are given and the techniques for making the assignments are discussed. The method presented could, in principle, be applied to any copolymer or terpolymer. Limitations that are encountered in the analysis of hydrogenated butadiene–styrene copolymers high in 1,2 additions are discussed.