High resolution NMR spectroscopy of heteroaromatic cations. II—pyrylium,thiapyrylium and seleninium cations

The barriers to internal rotation about the C? N bond in several thiopiperidides have been determined by the NMR technique. It was found that the barrier height (ΔG^?) increases in the series cinnamoylthiopiperidide<thiobenzoylpiperidide<phenylthioacetylpiperidide. This trend was discussed in terms of the electronic structure, using HMO calculations. For m-and p-substituted cinnamoylthiopiperidides the barriers were shown to increase with the electron withdrawing character of the substituent in the aromatic ring.     

Synthesis and NMR spectra of tetrahydrofuran-2-13C

An original method was developed for the synthesis of THF labeled selectively with the ¹³C isotope at the α-carbon atom. The effective reduction of symmetry brought about by the insertion of the isotopic label removes the excess degeneracy of the spin systems describing the multiplet structure of the ¹H and ¹³C NMR spectra, making it possible to undertake a detailed analysis. Exact values for the ¹H–¹H spin-spin coupling constants through four bonds and also the ¹³C–¹H and ¹³C–¹³C spin-spin coupling constants involving the α-carbon atom were determined for the first time. The isotopic chemical shifts of the protons and ¹³C nuclei caused by replacement of the ¹²C nucleus by ¹³C were determined. These data can be used to construct a quantitative model of the conformational behavior of THF as a molecular system in which pseudorotation in terms of vibrations with large amplitude is realized.     

1H and 13c NMR spectra of 8- hydroxyquinoline

The ¹H and ¹³C NMR spectra of 8-hydroxyquinoline were analyzed. The assignment of the signals was established unambiguously by ¹³C-{¹H} double-resonance experiments and investigation of the ¹³C NMR spectrum without decoupling from the protons.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1235–1236, September, 1977.     

Electronic spectra of 1-methyl and 2-methyl phenanthrenes and their radical cations

Electronic spectra of phenanthrene (P), 1-methyl phenanthrene (1-MeP), 2-methyl phenanthrene (2-MeP) and their monopositive ions are investigated experimentally as well as theoretically. The ions were produced by photo-oxidation of the hydrocarbons in boric acid matrix. The electronic absorption spectrum of 2-methyl phenanthrene cation (2-MeP+) is entirely new. For the interpretation of the electronic spectra of neutral and ionized MePs, semi-empirical AM1 (Austin Model 1) calculations are carried out for the first time. The bathochromic shifts in the spectral bands of the neutral and ionized MePs are attributed to 'conjugative' effect. The present experiments reveal that the 448 nm band of 1-methyl phenanthrene cation (1-MeP+) and the 486 nm band of 2-MeP+ show close matching with the respective 450 nm and 488 nm 'diffuse interstellar bands'. This suggests the possibility of the existence of such ionic species in the interstellar matter.     

Charge dispersal in 1- and 2-adamantyl cations

Substituents at the remoter 5-position of 2-adamantyl arylsulfonates control solvolysis rates more strongly than substituents at the 4-position.     

Proton-coupled 13C NMR spectra of 2- and 3-substituted pyridines

The proton-coupled ¹³C NMR and PMR spectra of pyridine and the 2- and 3-monosubstituted pyridines NC₅H₄X [where X=CH₃, CN, COCH₃, COOCH₃, N(CH₃)₂, NO₂, OCH₃, Cl, or Br] for one-molar solutions of the compounds in DMSO-D₆, have been analyzed. The signs and values of the ¹³C-¹H HSSCs have been determined. Equations have been obtained connecting the ¹³C-¹H SSCCs in the 2- and 3-substituted pyridines and the monosubstituted benzenes. A satisfactory correlation of ¹JCH with the F and R constants of the substituents has been shown.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1223–1230, September, 1984.     

13C NMR spectra of some 1-, 3- and 4-monosubstituted and disubstituted isoquinolines

Chemical shifts and substituent chemical shift (SCS) effects are reported for 21 monosubstituted iso-quinolines, carrying a halogeno, amino, piperidino or ethoxy group in position 1, 3 or 4. In some cases, assignments of ¹³C resonances were based on the spectra of the corresponding 5-deutero derivatives. For the fluoroisoquinolines some ¹³CF coupling constants are given. The ¹³C NMR spectra of 15 disubstituted isoquinolines were measured; with a few exceptions, mainly the 3,4- and 1,4-disubstituted isoquinolines, the chemical shifts agreed well with those calculated by addition of the SCS effects.     

The mass spectra of 1- and 2-alkylbenzotriazoles

The fragmentation patterns of a series of 1- and 2-alkylbenzotriazoles are recorded and interpreted in comparison with available literature data. 1- and 2-Substituted benzotriazoles are readily differentiated on the basis of the relative ease with which a 1-substituted isomer loses nitrogen compared with the corresponding 2-isomer, resulting in generally weak parent ions for the former and strong parent ions for the latter. This loss of nitrogen in the 1-isomer ultimately gives rise to a strong peak at m/z 104, which is small or absent in the 2-isomer. In addition, examination of the intensity and distribution of peaks clustered around m/z 118 reveals that weak signals with a maximum intensity at m/z 117 or 118 are indicative of the 1-isomers, while strong signals with a maximum intensity at 119 or 120 are typical of the 2-isomers. Thus, isomers are distinguished by analysis of mass spectral cracking patterns. © 1997 John Wiley & Sons, Inc. Heteroatom Chem. 8: 459–464, 1997     

NMR spectra of 2-pyrone and 2-pyrone derivatives

An analysis of the complex NMR spectrum of 2-pyrone is presented and the spectra of a series of variously substituted 2-pyrones and 5,6-dihydro-2-pyrones are discussed. It is demonstrated that NMR spectroscopy affords a convenient and reliable method of assigning the position of substituents on the 2-pyrone nucleus.     

The 1H NMR spectra of p-substituted phenyl 2-chloro-2-fluoroethyl sulphides

The 60 MHz ¹H NMR spectra of p-substituted phenyl 2-chloro-2-fluoroethyl sulphides have shown characteristic patterns; in the ABC portion of an ABCX spin system (X = ¹⁹F) of the compounds, one of the subspectra shows an ABC pattern and the other apparently an AB₂ pattern. These spectral patterns have been analysed and the ¹H NMR data obtained are discussed briefly.     

NMR spectra and structures of protonated 1-vinylpyrroles

Stable 1-vinylpyrrolium fluorosulfonates were prepared by the reaction of 1-vinylpyrroles with excess HSO₃F at –50°C in CD₂Cl₂ and their ¹H and ¹³C NMR spectra were obtained. Despite its overall positive charge, the pyrrole ring remains an electron donor relative to the vinyl group. Delocalization of the positive charge onto substituents decreases in the order 2-heteroaryl > 2-aryl > 2-alkyl.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 48–57, January, 1993.     

Synthesis and 13C NMR spectra of cis- and trans-{2-(haloaryl)-2-[(1H-imidazol)-1-yl]methyl]}-1,3-dioxolane-4-methanols

Syntheses and ¹³C nmr spectra of a number of cis and trans 2-(haloaryl)-2-[(1H-imidazol-1-yl)rnethyl]-4-(hydroxymethyl)-1,3-dioxolanes are described. The haloaryl groups are 2,4-dichloro, 2,4-difluoro-, 4-chloro-and 4-bromophenyl. In these series, some of the cis compounds become available through crystalline bromo benzoates 5 . Separations of some trans isomers are achieved through fractional crystallizations of imidazolyl benzoate nitrates 6 . Stereochemical assignments are based primarily on one major ¹³C chemical shift difference, namely that of C-4 of the 1,3-dioxolane ring, the chemical shift of the trans isomers being 1.0-2.5 ppm downfield from that of the cis isomers.     

13C NMR spectra of 1-(N-arylidene)amino-1,2,3-triazoles

The ¹³C nmr spectra of several 1-(N-arylidene)amino-1,2,3-triazoles were determined. The long range influence of substituents on ¹³C resonances of triazole and C = N carbon atoms was examined and a correlation of their chemical shifts with net charge densities (q_{π + σ}) calculated by the CNDO/2 method was made. It was also shown that the dependence of the coupling constants ¹J(CH) for C = N carbon on the substituents is better correlated using electrons in bond values instead of charge densities.     

1H NMR spectra of monosubstituted phenanthrenes

The effects of various substituents on the chemical shifts and coupling constants of the ¹H NMR signals of phenanthrene are reported and discussed in terms of structural features.     

13C and proton NMR spectra of 2(1H)pyrazinones

¹³C and proton NMR spectra data are given for eleven 2(1H)pyraziones. Assignments of chemical shifts were made by methods which included: deuterium exchange with certain protons of 3-alkyl substituents; change of chemical shifts of certain carbon atoms with change in pH; the use of long-range coupling constants for ¹³C to protons; and various correlations among assigned spectra.