Nitrogen-15 nuclear magnetic resonance spectra of ketenimines

Nitrogen-15 NMR spectra of 11 ketenimines have been taken both at the natural-abundance level of ¹⁵N and with the aid of ¹⁵N-labeling. The nitrogen chemical shifts are substantially different from those of neutral imines and are upfield, more like those of protonated imines. The results are in accord with significant delocalization of the nitrogen lone-pair. Furthermore, there is a rough parallelism between the ¹³C shifts of the terminal carbons and the ¹⁵N shifts.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. Pyridine N-oxides and quinoline N-oxides

The noise-decoupled nitrogen-15 NMR spectra of ten pyridine N-oxides and two quinoline N-oxides have been obtained at the natural-abundance level by high-resolution NMR spectroscopy. Substituents at the 4-ring position of pyridine N-oxide, capable of resonance interaction with the N-O moiety, give fairly large shifts in the expected directions. Spectra taken in dimethyl sulfoxide solution give 5–20 ppm and 33–55 ppm downfield shifts with respect to the solutions of the same substances in 2,2,2-trifluoroethanol and trifluoroacetic acid. Solvent influences are discussed in terms of hydrogen bonding and protonation of the N-oxide oxygen. Carbon-13 chemical shifts and one-bond carbon-hydrogen coupling constants of some substituted pyridine N-oxides are reported and discussed.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. Natural abundance nitrogen-15 spectra of the cis and trans isomers of secondary alkylformamides

The ¹⁵NMR chemical shifts were measured of a number of N-substituted formamides and acetamides at the natural abundance level. The ratios of the cis and trans isomers for several N-alkylformamides were also determined. Substituent effects on the ¹⁵N chemical shifts of formamides are compared with those of some other nitrogen-containing compounds. There is a consistent pattern of behavior of the one bond spin–spin coupling constants [¹J(¹⁵NH)] wherein the trans isomers of N-alkylformamides are larger than those of the cis isomers.     

Nitrogen-14 nuclear magnetic resonance of azine-N-oxides

The ¹⁴N NMR chemical shifts of mono-N-oxides of 1,2-, 1,3-, and 1,4-diazine systems in mono-, bi, and tri-cyclic structures are shown to depend linearly on the π-charge density at the oxide nitrogen atom obtained from SCF-PPP-MO calculations. The ¹⁴N NMR chemical shifts in poly-azine-mono-N-oxides relative to parent structures of mono-azine-N-oxides may be expressed in terms of additivity rules for 1,2-, 1,3-, and 1,4-interactions of azine type nitrogen atoms. Simple additivity rules are also found for an influence of fused ring systems. Nitrogen chemical shifts, hitherto unknown, are predicted for a number of poly-azine-mono-N-oxide structures.     

Nitrogen-15 magnetic resonance spectroscopy XVI—natural-abundance spectra of aromatic amines

The ¹⁵N chemical shifts of aniline, the toluidines, xylidines, and several halogen and oxygen substituted anilines have been measured at the natural abundance level of ¹⁵N. Substituent parameters obtained by multiple regression analysis show that the methyl group induces comparable upfield shifts at the ortho and para positions (2·37 and 2·55 ppm/methyl, respectively) and a small (0·77 ppm/methyl) upfield shift at the meta position. The chemical shifts correlate reasonably well with ¹⁹F shifts of similarly substituted fluorobenzenes, with C-1 of the anilines themselves and with Hammett sigma values. While the shifts of C-methyl substituted anilines do not correlate with the methyl resonances of corresponding polymethylbenzenes, those of the halo- and alkoxyanilines show a reasonable parallelism with corresponding ¹³C-methyl shifts. The results are interpreted in terms of possible modes of transmission of electron density in an alternating and additive manner through the sigma framework.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. Chemical shifts of methyl substituted cis-decahydroquinolines

¹⁵N Chemical shifts of cis-decahydroquinoline, N-methyl-cis-decahydroquinoline, and of 19 methyl substituted NH- and NCH₃-cis-decahydroquinolines are reported. Shift values of conformationally homogeneous compounds can be used to determine the chemical shifts of the possible conformations of the mobile compounds. Equilibrium constants derived from the shifts of the contributing conformations agree with results of low temperature ¹³C NMR spectroscopy.     

Nitrogen-15 nuclear magnetic resonance spectroscopy as a probe for the study of membrane models

¹⁵N NMR spectroscopy has been used to investigate liposomes from an enriched phospholipid (dipalmitoyl-phosphatidylcholine). It is shown that this probe can yield interesting information on the dynamics of head groups and on some interactions at the lipid–water interface. Even large multilamellar vesicles give rise to narrow, symmetrical signals, with a maximum nuclear Overhauser effect over the phase transition temperature. The sensitivity of the technique as regards structural changes was demonstrated by a complete study made between 20 and 60°C.     

Nitrogen nuclear magnetic resonance spectroscopy. Nitrogen-15 and proton chemical shifts of methylanilines and methylanilinium ions

Nitrogen and carbon electron densities of the toluidines and xylidines have been recalculated by the INDO method; previously published errors have been corrected. Although the nitrogen-15 chemical shifts of these compounds still display the earlier suggested correlation with σ and total electron densities, the calculated inverse correlation with proton electron densities has been shown to be incorrect. Methyl proton chemical shifts of these compounds display no meaningful correlation with the nitrogen shifts. The nitrogen chemical shifts of the toluidinium and xylidinium ions correlate moderately well with the ¹³C chemical shifts of the analogous di- and tri-methylbenzenes.     

15N nuclear magnetic resonance spectroscopy. Natural-abundance 15N spectra of aliphatic oximes

¹⁵N chemical shifts of the Z and E isomers of twenty-two ketoximes and fourteen aldoximes have been determined at the natural-abundance level of ¹⁵N, using Fourier transform methods. The influences of π delocalization, methyl substituents and solute concentration on the oxime nitrogen shielding have been determined. The ¹⁵N shifts for oximes of several cycloalkanones have been measured and the influence of ring size on the chemical shifts is discussed.     

Nitrogen-15 nuclear magnetic resonance spectroscopic study of compounds with nitrogen?nitrogen bonds

The ¹⁵N NMR spectra of several substances with nitrogen—nitrogen bonds have been obtained at the natural-abundance level by high-resolution NMR spectroscopy. Azo (? N?N? ) nitrogens are 300–500 ppm deshielded compared with hydrazo (? NH? NH? ) nitrogens. The sensitivity of the ¹⁵N shifts in these types of substances to substituent changes are reported, along with ¹⁵N–¹H spin–spin couplings for some hydrazo compounds. Hydrogen-bonding effects arising from solvent changes on the ¹⁵N shifts of azoxybenzene are different for its two kinds of nitrogen. The ¹⁵N NMR spectrum of N,N'-dinitrosopiperazine in dimethyl sulfoxide at room temperature is consistent with the presence of two different conformations about the N? NO bonds.     

Systematic series of azacycl[3.3.3]azines of varying nitrogen content: Nitrogen-15 magnetic resonance spectra

Nitrogen-15 NMR spectra were obtained for a systematic series of azacycl[3.3.3]azines: 1,3,4,6,7,9-hexaaza-,1,3,4,6,7-pentaaza-,1,3,4,6-tetraaza-, 1,3,4,6,8-pentaaza-, and 1,3,6-triazacycl[3.3.3]azine. The magnetic resonance data were compared with other physical and spectroscopic properties available for the series relative to the diminishing number of peripheral nitrogens in alternating positions. The properties of 1,3,4,6,8-pentaazacycl[3.3.3]azine, which has a peripheral 1,4-diazine-type nitrogen, are distinct from those of the rest of the series.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. 15N?19F coupling constants in fluoropyridines and fluoroanilines

Two-to five-bond ¹⁵N? ¹⁹F coupling constants have been determined for fluoropyridines, 8-fluoroquinoline, fluoroanilines and fluoroaniline derivatives. Only in 2-fluoropyridine is J(NF) large, and this is associated with a lone pair mediated enhancement of the coupling. Values in fluoroanilines and derivatives are <2Hz. Except for the fluoroanilines themselves, J(NF) decreases inversely with the number of intervening bonds. In the anilines, only ⁵J(NF) is observable. Possible influences of lone pair interaction and hydrogen bonding are discussed.     

The carbon-13 and nitrogen-15 nuclear magnetic resonance spectra of uroporphyrinogens I and III

Due to their sensitivity to light and air, porphyrinogens are not normally isolated, but are routinely analyzed by oxidation to the corresponding porphyrin. We report herein the ¹³C- and ¹⁵N-NMR spectra of uroporphyrinogens I and III in their “native state”, multiply labelled with ¹³C and ¹⁵N, and at natural abundance (¹³C only).     

Synthesis and nuclear magnetic resonance spectra of fused pyrimidines

Ethy phenylpropiolate reacted with 2-aminobenzothiazoles, benzimidazoles, thiazoline and thiazole to give the corresponding fused 2-oxopyrimidines. 2-Mercaptobenzimidazole reacted with ethyl phenylpropiolate to give 4-phenyl-2H-1-thiapyrimido(1,2-a ]benzimidazol-2-one in very good yield. The thiones, methylthio iodides and the hydrobromides of some of the products were prepared. Analysis of the nmr spectra of the benzothiazole and benzimidazole products and their 3-deuterio analogs showed that the proton at position 6 is shielded and absorbs together with the proton at position 3 near δ 6.0 ppm. The nmr and ir spectral data of all the products are tabulated and discussed.