Specific intramolecular C-H...O interactions in 1-vinyl-2-formylimidazole and 1-vinyl-2-formylbenzimidazole studied by1H and13C NMR spectral data

According to the¹H and¹³C NMR spectral data, the vinyl group in 1-vinyl-2-formylimidazole and 1-vinyl-2-formylbenzimidazole istrans-oriented with respect to the formyl fragment, while the carbonyl group occupies theanti-position with respect to the N atom of pyridine cycle. A specific intramolecular C—H...O interaction of a weak hydrogen bond type is realized between the -H atom of the vinyl group and O atom of the carbonyl group.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1197–1201, May, 1996.     

Comparison of the effects of the intra- and intermolecular hydrogen bonds C-H...X (X = O,N) in1H and13C NMR spectra

A similarity between manifestations of the effects of the intra- and intermolecular hydrogen bonds C-H...X (X = O, N) in¹H and¹³C NMR spectra has been shown. A correlated increase in the direct spin-spin coupling constant¹³C—¹H and the chemical shifts of the proton participating in the interaction has been observed.Translated fromIzvestiya Akademii Nauk. Seriyo Khimicheskaya, No. 5, pp. 1205–1207, May, 1996.     

Influence of the position of the nitro group on the structural and spectroscopic characteristics of N"-(nitrobenzylidene)isonicotinic hydrazides in the crystalline state

N"-Substituted isonicotinic hydrazides of the general formula Py—C(=O)—N(H)-N"=C(H)—R, where R is o- (1), m- (2), or p-nitrophenyl (3), were studied by IR spectroscopy and X-ray diffraction analysis. The position of the nitro group in these compounds has no effect on the type of the crystal structure. The crystal packings are based on stacks consisting of antiparallel planar molecules. The molecules from the adjacent stacks are linked to each other via the N—H...N_Py hydrogen bonds. Depending on the position of the nitro group, the N...N_Py distance increases in the series 3 > 1 > 2 and the energy of the hydrogen bonds decreases (according to the IR spectroscopic data) from 3.9 to 3.1 kcal mol^–1. Analysis of the IR spectra demonstrated that the intensity of absorption in the (C—H) stretching region of the pyridine ring increases substantially as the the N—H...N_Py hydrogen bond is strengthened. Some regularities of the changes, which are observed for the (NO₂) bands in the spectra of the nitrophenyl-containing conjugated molecules in solutions, persist in the crystalline state.     

Analysis of effect of specific C-H ...X interaction on the direct13C-1H spin-spin coupling constants based onab initio quantum-chemical calculations

Anab initio quantum-chemical calculation of the direct^13C–¹H spin-spin coupling constants in the CH₄–H₂O system was carried out and experimental data obtained for a series ofN-vinyl compounds were analyzed. The specific C-H ....X (X = O, N) intramolecular interactions result in increasing the direct¹³C–¹H spin-spin coupling constant of the hydrogen involved in bonding and decreasing the direct¹³C-¹H spin-spin coupling constant for the hydrogen atom that takes no part in the interaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1362–1365, Tune, 1996.     

Dependence of geminal1H−1H and31P−1H spin-spin coupling constants on the specific intramolecular C−H...X interaction

Participation of the proton in a specific intramolecular C−H...X (X=N, 0) interaction leads to an increase in its geminal¹H−¹H and¹H−³¹P spin-spin coupling constants (SSCC). According toab initio calculations carried out in the 6–31G^** basis set, the observed effect is mainly due to the change in the diamagnetic spin-orbital contribution to SSCC. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 306–309, February, 1997.     

X-ray and IR spectroscopic studies of specific intermolecular interactions inN′-substituted isonicotinohydrazides

_N-Thenylidene- andN-(o-nitrobenzylidene)hydrazides of isonicotinic acid have been studied by X-ray structural analysis and IR spectroscopy. In the crystalline state, these molecules are linked through intermolecular N—H ... Np_y hydrogen bonds. Carbonyl groups are not involved in intermolecular hydrogen bonds. However, it was found that the C=O group participates in an attractive interaction with the sulfur atom of the thiophene group. The energy of this interaction is comparable with the energies of intermolecular C=O ... H—N hydrogen bonds in amides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 896–900, April, 1996.     

The Molecular Structure and NMR Properties of P-Phosphinoylmethyl Aminophosphonium Salts

The molecular structures of two aminophosphonium salts (bromide and tetrafluoroborate) have been determined by X-ray analysis. They have similar conformations and hydrogen bond (HB) networks: the N–H acid proton is bonded to the anion and, in the case of the fluoroborate, to the oxygen atom of the phosphine oxide, forming a pseudo six-membered ring closed by a weak N–HO intramolecular hydrogen bond (IMHB). These compounds have been studied by multinuclear NMR in solution, including the ¹⁵N-labeled derivatives, to determine a complete set of coupling constants. A coupling of 1.5 Hz between the ¹⁵N and the ³¹P nuclei, separated by three bonds, was observed experimentally for the bromide in CDCl₃ solution, which appears to be a classical ³ J _N-P across the covalent bonds and not a ^3h J _N-P across the IMHB.     

Transformations of the chiral diphosphine rhodium catalyst [(1,5-COD)Rh(—)R,R-DIOP]+CF3SO3– under conditions of hydrogenation

Transformation products of the cationic rhodium complex [(1,5-COD)Rh(—)R,R-DIOP]⁺CF₃SO₃ ^– (1) (COD is cycloocta-1,5-diene and DIOP is (±)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane), which were obtained in its reactions with molecular hydrogen, base (NEt₃), and solvents in the absence of a substrate, were investigated by ¹H and ³¹P NMR spectroscopy. The solvate complexes [(Solv)₂Rh(—)R,R-DIOP]⁺CF₃SO₃ ^–, which were generated from complex 1 in its reaction with molecular hydrogen, underwent destruction of the diphosphine ligand with elimination of benzene and were subjected to oxidation by traces of moisture and oxygen to form the DIOP dioxide complex with Rh^I. In the absence of hydrogen, complex 1 in solutions produced the diphosphine dioxide rhodium(i) complex and mono- and binuclear rhodium(i) solvate complexes. The scheme of deactivation of the complex in the absence of the substrate was proposed. The catalytic activity of the solvate complexes [(ArH)Rh(—)R,R-DIOP]⁺CF₃SO₃ ^–, which contain benzene, p-xylene, and mesitylene in the coordination sphere, was studied in hydrogenation of Z--acetamidocinnamic acid.     

1-Methyl-2(3,4)-(1-vinylpyrrol-2-yl)pyridinium iodides: some structural features revealed by 1H and 13C NMR spectroscopy

The reactions of 2-, 3-, and 4-(1-vinylpyrrol-2-yl)pyridines with methyl iodide afford the corresponding quaternary salts. Analysis of their ¹H and ¹³C NMR spectra showed that the quaternization of the nitrogen atom considerably enhances the -acceptor effect of the pyridine ring on the pyrrole ring and on the vinyl group. 1-Methyl-2-(1-vinylpyrrol-2-yl)pyridinium iodide contains no weak intramolecular C--H...N hydrogen bond present in the starting compound.     

Crystal structure of an uncomplexed 25-crown-7 comprising one 2,6-pyridino and two 1,4-benzo condensations

Single crystal X-ray analysis of the uncomplexed crown macroring 1 is reported. Crystals are triclinic, , witha=10.809(1),b=10.945(1),c=10.256(1) Å, =107.85(1), =104.15(1), =87.27(1)°,D _c=1.318 g cm^–3,Z=2. Three torsion angles in the macrocycle take upgauche conformations in contrast to the usualanti conformation. The crystal structure is stabilized by intramolecular van der Waals forces and weak C–H...O and C–H...N hydrogen bond attractions. Stacking of pyridine rings is a noticeable packing feature in the crystal lattice. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82168 (6 pages).Macroring Uncharged Molecule Complexation. Part 20. For Part 19 of this series see Ref. [1].     

Long-range13C—19F NMR spin-spin coupling in some α-trifluoromethyl-substituted polychloropyridines

High resolution¹³C NMR spectra of a series of -trifluoromethyl-substituted polychloropyridines were studied. Long-range¹³C—¹⁹F NMR spin-spin coupling through four and five bonds involving carbon atoms of the pyridine ring and the fluorine atom of the CF₃ group was found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1973–1974, October, 1995.     

Nitropyrazoles

The structures of substitutedN-aminonitropyrazoles and 1- and 2-amino-4-nitro-1,2,3-triazoles as well as the site of protonation of 1-aminopyrazole were determined based on the¹H,¹³C, and¹⁵N (¹⁴N) NMR spectra. The¹³C NMR spectra were recorded under conditions of¹³C-{¹H,¹⁴N} triple resonance. Effects of substituents in the pyrazole ring on the¹³C and¹⁴N chemical shifts were studied. The¹³C,¹H and¹⁵N,¹H spin-spin coupling constants, obtained using techniques of [¹H]¹³C and [¹H]¹⁵N polarization transfer (SPT, INEPT), were measured, fully assigned, and discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2181–2186, November, 1995.For Part 8, see Ref. 1.     

Molecular structure of di-aryl-aldimines by multinuclear magnetic resonance and X-ray diffraction

The complete ¹H, ¹³C and ¹⁵N NMR analyses for a series of 25 diaryl-aldimines containing phenyl, pyridyl, pyrazolone and furanyl moieties are described herein. Detailed evaluation of substituent chemical shift and coupling constant effects showed that interaction between the lone pair of the pyrazolone carbonyl group or the nitrogen of 2-substitued pyridines with the aldimine hydrogen increases the value and shifts the resonance signal for this hydrogen to high frequency, in the ¹H NMR spectra. The X-ray crystal structure analysis of pyrazolone substituted aldimines evidenced the planarity of the aryl groups which are conjugated with the CN double bond. In the case of the N-(2-pyridinemethylene)-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one, two rotamers were observed in the same unit cell.     

Structural and spectroscopic characteristics of α-cyano-substituted α-phosphoryl(thiophosphoryl)acetonates in neutral chelate-bridged complexes. Crystal structure of [Cu[(PrO)2P(O)C(CN)C(Me)O]2]

A comparative study of the three-dimensional and electronic structures of the chelate salts (ML _n ) of enol forms of -cyano-substituted -phosphoryl- and -(thiophosphoryl)acetones (RO)₂P(X)C(CN)C=CMe(OH) (X = O or S; R = Pr or Et) with the Cu^I, Cu^II, and Co^II cations was carried out. In all complexes under consideration, the geometry of the central moiety of the O—C(Me)—C(CN)—P chelate-bridging ligand remains unchanged. The substantial electron delocalization involving the cyano group is observed in the O—C—C(CN)—P(X) ligand framework. The structure of the bis-chelate Cu[(PrO)₂P(O)C(CN)C(O)Me]₂ complex was established by X-ray diffraction analysis at 180 K and vibrational (IR and Raman) spectroscopy. The study in the temperature range from 290 to 140 K revealed the phase transition at 200 K accompanied by a change in the coordination polyhedron about the copper cation from a symmetrical octahedron (4+2 coordination) to a strongly unsymmetrically distorted octahedron (4+1+1 coordination). In both crystal modifications, four oxygen atoms form the base of the octahedron, and the axial positions are occupied by the nitrogen atoms.     

Comparison of Ab Initio MP2/6-311+G(d,p) Predicted Carbon–Hydrogen Bond Distances with Experimentally Determined r 0 (C–H) Distances

Fifty different carbon–hydrogen distances have been predicted from ab initio MP2/6-311+G(d,p) calculations, which range from a short value of 1.0611 Å for HCNO to a long value of 1.1044 Å for H₂CO. The values include those predicted for a series of methyl (CH₃) moieties where the two different C–H distances vary by as much as 0.005 Å. These predicted values are compared to r ₀(C–H) distances obtained from the isolated carbon–hydrogen stretching frequencies, as well as to r ₀ or r _s parameters obtained from microwave data. Except for the very short C–H bonds, the ab initio values from the MP2/6–311+G(d,p) calculations can be used for the carbon–hydrogen distances with error limits of ± 0.003 Å. By utilizing the spectral data from CD₃CClO, it is shown that combination bands in the C–H stretching region could cause problems in the identification of the isolated C–H stretching frequency from the CD₂HCClO isotopomer. The value of the ab initio predicted C–H distances for checking unusually long or short r _s (C–H) or r ₀ values is demonstrated.     

Synthesis,crystal structure and magnetic properties of a two-dimensional mixed-valence assembly [Fe(salen)]2[Fe(CN)5NO]

A cyanide-bridged Fe^III–Fe^II mixed-valence assembly, [Fe^III(salen)]₂[Fe^II(CN)₅NO] [salen = N,N-ethylenebis(salicylideneiminato)dianion], prepared by slow diffusion of an aqueous solution of Na₂[Fe(CN)₅NO] · 2H₂O and a MeOH solution of [Fe(salen)NO₃] in an H tube, has been characterized by X-ray structure analysis, i.r. spectra and magnetic measurements. The product assumes a two-dimensional network structure consisting of pillow-like octanuclear [—Fe^II—CN—Fe^III—NC—]₄ units with dimensions: Fe^II—C = 1.942(7) Å, C—N = 1.139(9) Å, Fe^III—N = 2.173(6) Å, Fe^II—C—N = 178.0(6)°, Fe^III—N—C = 163.4(6)°. The Fe^II—N—O bond angle is linear (180.0°). The variable temperature magnetic susceptibility, measured in the 4.8–300 K range, indicates the presence of a weak intralayer antiferromagnetic interaction and gives an Fe^III–Fe^III exchange integral of –0.033 cm^–1.     

Evidence for the synchronous cleavage of C—C and C—H bonds bis(2,2′-bipyridyl)copper(II) permanganate oxidation of cobalt(III) bound and unbound α-hydroxy acids

The kinetics of bis(2,2-bipyridyl)copper(II) permanganate oxidation of Co^III bound and unbound -hydroxy acids such as mandelic, lactic and glycolic acids have been studied in aqueous MeCO₂H. The reaction exhibits second order kinetics: first order in each reactant. The formation of Co^II, PhCHO and CO₂ to the extent of 24% [Co^III]_initial indicate C—bonds;H cleavage occurring to the extent of 24% and ca. 76% yield of the phenylglyoxylato-pentaamminecobalt(III) complex indicate C—H cleavage occurring to the extent of 76%.     

Chiral photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophen-3(2H)-ones

Photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophen-3(2H)-ones containing ortho-substituents in the N-phenyl ring were studied by X-ray diffraction analysis and ¹H NMR spectroscopy. It was established that these compounds have stable chiral structures due to hindered rotation of the phenyl ring around the C—N bond. The energy barrier to racemization evaluated by dynamic NMR spectroscopy is G ^# _{428 K} = 98 kJ mol^–1.     

Specific C-H⋯N intramolecular interactions in the vinyloxy- and vinylthiopyridine series

A weak hydrogen bond with the participation of the vinyl group -hydrogen atom arises in 2-vinyloxypyridine and 2-vinylthiopyridine, which primarily exist in the s-trans-conformation, according to the ¹H and ¹³C NMR data. This interaction does not take place in 2-vinyloxymethyl- and 2-vinyloxyethylpyridines, which primarily exist in the s-cis-conformation. The C-H...N intramolecular interaction also does not occur in o-vinyloxyaniline due to the specific features of the stereoelectronic state of the amino group nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1077–1081, August, 1991.     

Quantitative 2H NMR spectroscopy. 1. Thermodynamic H/D isotope effects in N,N-dimethylformamide and cyclopentadiene molecules

A new method for quantification of the relative distribution of deuterium in molecules is proposed. The technique is based on the lineshape analysis in the ²H NMR spectra obtained at the natural abundance level of deuterium with allowance for inhomogeneity of the magnetic field. The equilibrium thermodynamic H/D isotope effects for hindered rotation about the C—N bond in the N,N-dimethylformamide molecule and for prototropic exchange in the cyclopentadiene molecule were determined. The results obtained agree with those of DFT calculations of the vibrational energies.