Bohdan Kamieński

The 15N and 13C solid state NMR study of intramolecular hydrogen bond in some Schiff's bases

A series of 11 Schiffs bases derived from substituted salicylaldehyde and aliphatic amines has been studied in the solid state by 15N and 13C cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR). 15N CPMAS is especially useful for investigation of the tautomerism in the compounds considered, owing to the large difference in the nitrogen chemical shifts of OH and NH tautomers. In the solid state, three of the compounds examined were shown by 15N NMR to exist as OH tautomeric forms, and the remaining eight as the corresponding NH forms. This was confirmed by 13C CPMAS. The results reported were compared with those obtained in CDCI3 solutions.

Intramolecular hydrogen bond investigations in Schiff bases derivatives of 2-hydroxy-1-naphthaldehyde and 2-hydroxy-1-acetonaphthone in CDCl3 solution and in the solid state by NMR methods

Abstract Three Schiff bases: 1-( N -methyl-iminomethyl)-2-naphthol ( I ), 1-( N -isopropyl-iminomethyl)-2-naphthol ( II ) and 1-( N -isopropyl-α-iminoethyl)-2-naphthol ( III ) have been investigated by 15 N and 13 C NMR spectroscopy in order to study the tautomeric equilibrium in both the solid and liquid phases. For two derivatives of 2-hydroxy-1-naphthaldehyde ( I and II ), the NH tautomers have been found to be dominant in both the phases. The Schiff base derived from 2-hydroxy-1-acetonaphthone ( III ) exists in the CDCl 3 solution mainly in the NH form but in the solid state only the OH tautomer has been detected. The steric effect of the methyl group at the imine carbon atom seems to be responsible for such exceptional behaviour of the Schiff base investigated. Additionally, the principal components of 15 N chemical shift (CS) tensor of the compound III and two model compounds (5-methoxy-salicylidenmethylamine ( IV ) and 4-methoxy-salicylidenemethylamine ( V )) have been measured to confirm the electronic structure of III .

Spectroscopic studies of Schiff bases of 2,2'-dihydroxybiphenyl-3-carbaldehyde and para substituted anilines

Abstract Five Schiff bases derivatives of 2,2′-dihydroxybiphenyl-3-carboxaldehyde and various para substituted anilines have been synthesised and studied by FT-IR, 1 H, 13 C, 15 N NMR and CPMAS spectroscopy. The structure of the Schiff base includes two intramolecular OH⋯O and OH⋯N hydrogen bonds forming a hydrogen-bonded chain. All Schiff bases studied exist in imine form in chloroform and acetonitrile solution. On the basis of the CPMAS and FT-IR spectra in solid state the SCH5 base has been proved to exist in the enamine form.

15N NMR study of the intramolecular hydrogen bond in N-salicylidene-alkylamines

Abstract 15 N NMR spectra of a series of N -(R-salicylidene)-alkylamines in CDCl 3 solution were measured. Proton transfer equilibrium has been established on the basis of the temperature dependence of the 15 N chemical shift and 1 J NH coupling constants.

Heteronuclear multiple-quantum correlation 15N–1H, cross-polarized magic angle spinning 13C, 15N nuclear magnetic resonance and infrared spectroscopic studies of 1,2,4-triazolo-[1,5α]-pyrimidine and its Zn(II) halide and thiocyanate complexes

Abstract 1,2,4-Triazolo-[1,5α]-pyrimidine (tp) was studied by gradient heteronuclear multiple-quantum correlation 15N–1H NMR and by cross-polarized magic angle spinning 13C, 15N NMR. The 15N signals were unambiguously assigned. The assignments of some IR absorption bands were proposed by comparison to purine and adenine spectra. The obtained results were used for the investigation of Zn(tp)2X2-type complexes (X=Cl, Br, I, NCS), suggesting a pseudo-tetrahedral configuration around the Zn(II) ion with unidentately N(3) bonded heterocycles and halides or thiocyanates (N bonded) in terminal positions. A slight shielding effect on the N(3) nucleus upon the formation of Zn(II)–N coordination bonding was observed.

NMR frequency and magnetic dipole moment of 3He nucleus

We present new gas-phase NMR spectra which relate the resonance frequency of (3)He nucleus to the resonance frequency of the proton in tetramethylsilane (TMS). We discuss the dependence of (3)He resonance frequency on the density of the solvent gas, and we consider in detail the absolute shielding scales of both nuclei. Finally, we analyse the accuracy of the results, using the relationship between the resonance frequencies, absolute shielding constants and magnetic dipole moments of (1)H and (3)He nuclei.

The NMR study of some macrocyclic and macrobicyclic Schiff bases in solution and solid state

One macrocyclic and two macrobicyclic Schiff bases have been synthesized and investigated by 1 H, 13 C and 15 N NMR spectroscopy in solid state and CDCl3 solution at different temperatures. The results obtained have shown that all studied Schiff bases in CDCl3 solution at ambient temperature exist in a fast dynamical equilibrium that leads to the averaged symmetrical structure. The presence of flexible aliphatic chains and possibility of formation of different intramolecular hydrogen bonds in II and III leads to several different conformations in CDCl3 solution at low temperatures. An asymmetry of the Schiff bases molecules in solid state has been established. q 2002 Elsevier Science B.V. All rights reserved.

CP/MAS spectroscopy in the determination of the tautomeric forms of gossypol, its Schiff bases and hydrazones in the solid state

New Schiff bases and new hydrazones were synthesized and studied by 13C and 15N CP/MAS spectroscopy and by 1H1H COSY, 1H13C HMBC, 1H13C HSQC, 1H15N HMQC and 1H15N HSQC correlations. The CP/MAS investigation of gossypol has demonstrated that in the solid state it exists exclusively in the aldehyde‐aldehyde tautomeric form. In contrast, CP/MAS studies of hydrazones and Schiff bases reveal that these compounds occur in the solid state in the N‐imine–N‐imine and enamine–enamine tautomeric forms, respectively. It is shown that the 13C resonances of C‐6, C‐7 and C‐11 carbon atoms are suitable for distinguishing between the tautomeric forms of aza‐derivatives of gossypol in the solid state. Furthermore, we have proved that the 15N CP/MAS spectra can be used to identify these tautomeric forms. Copyright

1H, 13C, 15N NMR and 13C, 15N CPMAS studies of cobalt(III)-chloride-pyridine complexes, spontaneous py → Cl substitution in trans-[Co(py)4Cl2]Cl, and a new synthesis of mer-[Co(py)3Cl3]

Abstracttrans-[Co(py)4Cl2]Cl·6H2O, mer-[Co(py)3Cl3] and mer-[Co(py)3(CO3)Cl] were studied by UV-Vis, far-IR and 1H, 13C, 15N NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of 1H NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands. 13C nuclei were deshielded upon Co(III) coordination, while 15N NMR studies exhibited ca. 85–110 ppm shielding effects (ca. 15–25 ppm more expressed for nitrogens trans to N than trans to Cl or O). 13C and 15N CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)4Cl2]Cl·6H2O and mer-[Co(py)3Cl3], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)4Cl2]Cl → mer-[Co(py)3Cl3] + py reaction was monitored by 1H NMR and UV-Vis. This process of py → Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)3Cl3] preparation.

A13C and15N NMR study of some furoxans and related compounds

Carbon and nitrogen NMR results are reported for a collection of furoxans and related compounds, taken on DMSO solutions. The15N chemical shifts and those of neighboring13C nuclei have characteristic values for the structures studied. Relative14N signal widths are used to identify the nitro group resonances. Valence tautomerism at room temperature is reported for one compound. The INADEQUATE technique is used to determine some1J(13C-13C) data.