Jaromír Toušek

15N NMR Spectroscopy in Structural Analysis: An Update(2001-2005)

Since our previous review article (Curr. Org. Chem. 2002, 6, 35), significant improvements and an array of 15N NMR applications in structural analysis have been published. This report aims to update coverage of improvements in methodology and various types of applications published over the period 2001 - 2005. Substantial progress in cryogenic probe technology and the commercial availability of cryoprobes have facilitated the measurement of 15N NMR parameters. The number of solid-state applications has increased significantly during the past few years. In contrast to our previous review, this article covers 15N solid-state studies. The 15N NMR chemical shifts of organic molecules are routinely measured by using cross-polarization magic-angle spinning (CP/MAS) techniques. The principal values of the chemical shift tensors can also be determined. 1H-15N and 2H-15N distance measurements made by means of 1H detection are currently used in NMR crystallography. User friendly quantum chemical programs allow for the routine calculation of 15N chemical shielding and indirect spin-spin coupling constants, especially using density functional theory (DFT). Applications of 15N NMR spectroscopy in various fields of chemistry are summarized here. Major sections represent tautomerism, complexation, protonation, and hydrogen bonding. The other topics comprise N-alkylation, N-oxidation, regioisomerism, and changes in configuration or conformation.

1H and 13C NMR study of quaternary benzo[c]phenanthridine alkaloids

1H, 13C and in some cases also 15N chemical shifts of quaternary benzo[c]phenanthridine alkaloids (fagaronine, chelerythrine, chelilutine, chelirubine, nitidine, sanguilutine, sanguinarine, and sanguirubine) were systematically studied by NMR spectroscopy and ab initio calculations. The assignment of signals in the 1H and 13C NMR spectra was obtained from 2D NOE and gradient‐enhanced single‐quantum multiple bond correlation (GSQMBC) experiments. The ab initio geometry optimization using Gaussian 94 at the RHF/6–31 G** level, followed by the calculation of chemical shielding using the deMon/NMR code at the IGLO II level, were carried out in order to rationalize the assignment of individual experimentally determined resonances. Copyright

Experimental and quantum‐chemical studies of 1H, 13C and 15N NMR coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with picolines

1H, 13C and 15N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with picolines, [Au(PIC)Cl3], trans‐[Pd(PIC)2Cl2], trans/cis‐[Pt(PIC)2Cl2] and [Pt(PIC)4]Cl2, were performed. After complexation, the 1H and 13C signals were shifted to higher frequency, whereas the 15N ones to lower (by ca 80–110 ppm), with respect to the free ligands. The 15N shielding phenomenon was enhanced in the series [Au(PIC)Cl3] < trans‐[Pd(PIC)2Cl2] < cis‐[Pt(PIC)2Cl2] < trans‐[Pt(PIC)2Cl2]; it increased following the Pd(II) → Pt(II) replacement, but decreased upon the trans → cis‐transition. Experimental 1H, 13C and 15N NMR chemical shifts were compared to those quantum‐chemically calculated by B3LYP/LanL2DZ + 6‐31G**//B3LYP/LanL2DZ + 6‐31G*. Copyright

1H, 13C and 15N nuclear magnetic resonance coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with phenylpyridines

1H, 13C and 15N nuclear magnetic resonance studies of gold(III), palladium(II) and platinum(II) chloride complexes with phenylpyridines (PPY: 4‐phenylpyridine, 4ppy; 3‐phenylpyridine, 3ppy; and 2‐phenylpyridine, 2ppy) having the general formulae [Au(PPY)Cl3], trans‐/cis‐[Pd(PPY)2Cl2] and trans‐/cis‐[Pt(PPY)2Cl2] were performed and the respective chemical shifts (δ  1 H , δ  13 C and δ  15 N ) reported. 1H, 13C and 15N coordination shifts (i.e. differences between chemical shifts of the same atom in the complex and ligand molecules:

NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives.

\Delta_{\rm {coord}}^{1_{\rm {H}}} = \delta_{\rm {complex}}^{1_{\rm {H}}} - \delta_{\rm {ligand}}^{1_{\rm {H}}}

Configurations and conformations of sanguinarine and chelerythrine free bases stereoisomers

,

Origin of the conformational modulation of the 13C NMR chemical shift of methoxy groups in aromatic natural compounds.

\Delta_{\rm {coord}}^{13_{\rm {C}}} = \delta_{\rm {complex}}^{13_{\rm {C}}} - \delta_{\rm {ligand}}^{13_{\rm {C}}}

New P–S–N containing ring systems. Reaction of 2,4-(naphthalene-1,8-diyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide with methylbis(trimethylsilyl)amine

,

Experimental and quantum-chemical studies of 15N NMR coordination shifts in palladium and platinum chloride complexes with pyridine, 2,2'-bipyridine and 1,10-phenanthroline.

\Delta_{\rm {coord}}^{15_{\rm {N}}} = \delta_{\rm {complex}}^{15_{\rm {N}}} - \delta_{\rm {ligand}}^{15_{\rm {N}}}

N7‐ and N9‐substituted purine derivatives: a 15N NMR study

) were discussed in relation to the type of the central atom (Au(III), Pd(II) and Pt(II)), geometry (trans‐/cis‐) and the position of a phenyl group in the pyridine ring system. Copyright