1H and 13C NMR Study of the Structure of Alkylthio Enyne Alcohols and Glycols

Steric structure of some alkylthio enyne alcohols and glycols was determined by ¹H and ¹³C NMR spectroscopy. Analysis of cross peaks in the 2M NOESY spectra showed that the double bond in these compounds has Z configuration. Criteria were found which indicate the position of the hydroxy-containing substituent with respect to the triple or double bond.     

Asymmetric nitrogen. 57. Investigation of the stereochemistry of aziridinecarboxylic acid derivatives by NMR

Conclusions The preferred trans configuration of 1,2-disubstituted aziridines and cis configuration of NH-aziridine-2-carboxylic esters were established by means of the¹H and¹³C NMR spectra and the two-dimensional NOESY and COSY-45 spectra.For previous communications see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1110–1121, May, 1988.     

Crystal structure of α-cyanoacrylic acid

An x-ray structural investigation of -cyanoacrylic acid has been carried out (R=0.058 on the basis of 767 reflections). The molecules in the crystal are joined by strong O–H...N hydrogen bonds in zigzag chains along the [101] direction. The relative arrangement of the double bonds of neighboring molecules does not satisfy the conditions for topochemical reactions in crystals of compounds with C=C double bonds, in agreement with the stability of the crystals of -cyanoacrylic acid toward illumination and prolonged exposure to x rays.A. N. Nesmeyanov Institute of Organometallic Compounds, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, pp. 139–143, March–April, 1991.     

Determination of the geometry of acetoxyendiynes and acetoxyenynes by NMR heteronuclear 13C?1H scalar couplings and 13C NMR chemical shifts. Structural assignment of the oxylipin natural products peyssonenynes A and B

Solution NMR methods were used for the structural characterization of the acetoxyendiyne E/Z configuration of the marine natural products peyssonenynes A and B and their synthetic analogs derived from palmitic acid. The scarcity of protons in the proximity of the olefin precluded the determination of the double bond geometry using ¹H NMR methods that rely on proton–proton scalar couplings or experiments such as NOESY or ROESY. Long range ¹H? ¹³C heteronuclear scalar couplings, ⁿJ_CH, measured with the 2D excitation sculptured indirect detection experiment (EXSIDE) proved useful and highly reliable for the analysis of the enol acetate geometry. In addition, it was found that the chemical shift of some carbon atoms in the proximity of the olefin was also sensitive to the double bond configuration of these molecules providing an even simpler way to determine their geometry. This protocol showed its robustness by similar analysis of simpler silyl‐protected acetoxyenynes derived from fatty acids. These NMR experimental results and stereochemical predictions were rationalized by DFT calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and Structures of New Enaminones

Two isomeric enaminones were obtained by reaction of ethyl 2-hydroxy-4-(4-hydroxy-6-methyl2H-pyran-2-on-3-yl)-4-oxo-2-butenoate (1) and amines (aniline, benzylamine, butylamine and tyramine) in ethanol. The structures of isomers were studied by ¹³C and ¹H NMR spectra, whereas in the case of isomers 2b, 3a, and 4a (Scheme 1), the crystal structures have been determined by single crystal X-ray diffractometry. The compounds 2b and 3a exist in the solid state as N–C=C–C=O, whereas 4a is in the N–C=C–C–OH tautomeric form (Scheme 2, form A and B, respectively). All three structures exhibit very short intramolecular hydrogen bonds of O–H···O [in the range 2.396(3) – 2.448(3) Å] and N–H···O [in the range 2.580(5) – 2.679(3) Å] type, that are reinforced by delocalization. The crystal structures are in addition stabilized by C–H···O weak hydrogen bonds. In 2b and 3a, the discrete dimers are formed by eight-membered ring containing hydrogen bonds; in 4a, the infinite chains along [1 0 1] direction are formed.     

Hydrogen bonding in high-resolution protein structures: a new method to assess NMR protein geometry

An analysis of backbone hydrogen bonds has been performed on nine high-resolution protein X-ray crystal structures. Backbone hydrogen-bond geometry is compared in the context of X-ray crystal structure resolution. A strong correlation between the hydrogen-bond distance, R(HO), and the hydrogen-bond angle, theta(NHO), is observed when the X-ray crystal structure resolution is <1.00 A. Ab initio calculations were performed to substantiate these results. The angle and distance limits found in our correlation for the backbone hydrogen-bond geometry can be used to evaluate the quality of protein structures and for further NMR structure refinement.     

Solution Conformation of Gramicidin S Determined by Nuclear Magnetic Resonance and Distance Geometry Calculation

The solution conformation of the homodetic decapeptide antibiotic Gramicidin S has been determined by two-dimensional ¹H NMR spectroscopy and distance geometry followed by energy minimization. All structures corresponding to energy minima have four intramolecular hydrogen bonds between Leu and Val residues.     

Multinuclear and two-dimensional NMR spectroscopy of monoazo derivatives of chromotropic acid

By the use of one-dimensional (¹H,¹³C, and¹⁵N) and two-dimensional NMR spectra (H,H-COSY, H,C-COSY, and NOESY), it has been established that the phenylazo derivative of chromotropic acid in DMSO has a quinonehydrazone structure; under normal conditions, there is no azo-quinonehydrazone tautomerism. Spectral evidence has been found for the distribution of intramolecular hydrogen bonds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2530–2535, November, 1989.     

A computational study of the effect of an external electric field on the geometry of selected donor–acceptor complexes

To understand the effect of Au and thiol atoms in octane molecule, a structural and charge density analysis has been carried out by high level ab initio quantum chemical calculations using MP2 and B3PW91 methods with the basis sets 6-311G(d,p) and LANL2DZ. The optimized geometries, specifically, the geometry obtained from both levels reveal the effect of S- and Au-atoms in octane molecule. An introduction of sulfur atom in octane molecule lengthen its backbone C–C bond distances, and further adding of Au-atom at the terminals of octane dithiolate stabilizes these distances. The bond densities of the C–C bonds of octane are 1.6 eÅ⁻³, these values are decreased significantly and the charges are largely depleted, when thiol and Au-atoms added in the octane molecule. The presence of negative Laplacian ²ρ(r) at bond critical points of C–C and C–H bonds, indicate, the charges are concentrated in these bonds, confirm that these bonds exhibit an open shell type interaction. The moderate values of density and the negative Laplacian of S–C bonds confirm the covalent character. The positive ²ρ(r) value of Au–S bonds, characterize, the bonding interaction is a closed shell interaction. The combined observed low value of electron density and the positive Laplacian of Au–S bond comprises, the gold and S interaction is not a covalent interaction, but it is a very weak coordination bond interaction. The small positive value of total energy density in Au–S bond indicates, the charges in these bonds are highly depleted and this is further confirmed by the Laplacian of bond characterization.     

Tilted amides in amino acid and peptide derivatives

Background: Amide bonds in peptides and proteins typically adopt planar cis or trans conformations. Conversions between cis and trans amide conformations are necessary for protein folding and for many other processes, but are difficult to achieve since they involve disruption of the planarity of the bond. As a first step to understanding cis-trans isomerization, we set out to synthesize and characterize peptides that mimic the tilted or twisted amide structures that are postulated to form the intermediate states in this process.Results: We have synthesized a model amino acid and four dipeptide derivatives containing a methyl-substituted aziridine residue. Single crystals of phenacyl (2R, 3R)-benzyloxycarbonyl-3-methyl-2-aziridinecarboxylate and phenacyl (2R, 3R)-acetyl-glycyl-3-methyl-2-aziridine-carboxylate were obtained. Using X-ray diffraction analysis, we determined that the amide nitrogens of the aziridine rings have tetrahedral sp³-like geometry with tilt angles in the range of 37–38°. The ¹³C-NMR spectra indicate that the amide carbonyl is dramatically shifted downfield as a consequence of the tilt.Conclusions: In peptides containing a substituted aziridine ring, the orbitals of the amide nitrogen are constrained into a tilted configuration. These peptides may mimic the transition state between cis and trans amide conformations. This technique thus provides a novel strategy for the study of isomerization and other biorecognition processes.     

X-ray-structural investigation of sesquiterpene esters of plants of the genus Ferula. II. Crystal and molecular structure of the humulane alcohol fexerol

An x-ray structural investigation of the humulane alcohol fexerol has been carried out: diffractometer, CuK radiation, 1426 reflections, direct method, R factor 0.105. The spatial structure of the fexerol molecule has been determined. The substituents in positions 2, 5, and 8 have the orientation. The double bond in the 3–4 position has the cis configuration.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 42–46, January–February, 1986.     

X-ray structural investigation of sesquiterpene esters from plants of the genus Ferula. III. Crystal and molecular structure of the germacrane ester chimganidin

An x-ray structural investigation of the germacrane ester chimganidin (diffractometer Cu K radiation, 1028 reflections, direct method, R factor 0.114) has been carried out. The stereochemistry of chimganidin has been established; it is 6-hydroxy-8-vanilloygermacra-l(10),4(5)-diene. The double bonds in the macro cycle have the trans configuration.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 436–439, July–August, 1986.     

Structure and spectroscopic properties of 2,4-dichloro-1-diethylamino-3, 5-diphenyl-1,3-pentadien-5-one,the product of the unusual reaction of triethylamine with (dibenzoylmethanato)antimony tetrachloride

The crystal and molecular structures of the title compound have been established by the X-ray diffraction method. The molecule has a bent configuration with a dihedral angle between the double bond planes of 43.2°. The double bonds are localized and have lengths of 1.351(6) and 1.355(6) Å. However vibrational and electronic spectroscopy indicate that the conjugation in the butadiene fragment is retained; this fragment is a conductor of the direct polar conjugation effect between the donor diethylamino group and the acceptor carbonyl group.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 267–269, February, 1994.     

Study of rotations around C=C and C-N bonds in dienic δ- aminocarbonyl compounds by the NMR method

Conclusions We determined the free activation energies of the rotations around the C =C and C -N bonds in some unsaturated aminocarbonyl compounds and studied their dependence on the substituents, number of double bonds, solvent, and the concentration. Explanations of the observed processes were proposed on the basis of the obtained data.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2013–2022, September, 1973.     

Tetraaryl-methane analogues in group 14—V. Distortion of tetrahedral geometryin terms of through-space π–π and π–σ interactions andNMR sagging in terms of π–σcharge transfer

44 members of thecompound series Ph_4−nMR_n (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph₃Sn (o-Tol) and PhSn (o-Tol)₃ were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. ²⁹ Si-, ¹¹⁹ Sn- and ²⁰⁷ Pb-NMR chemical shifts were determined in solution and in the solid state. ⁷³ Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups.     

Effect of double bond on the surface properties of aqueous solutions of eicosapolyenoic acids

Surface tensions of aqueous solution of eicosapolyenoic acids (EA) with 25 double bonds were measured by use of a Du Nöuy tensiometer at pH 7.80 and 25°C, and the effects of double bond on the surface properties of EA were investigated. The value of critical micelle concentration of EA increased twofold with increasing number of double bonds. The free energy for the adsorption per double bond at the air-water interface was estimated as 2.47 kJ (double bond)^–1, and the negative value of free energy for the adsorption of EA molecule decreased with increasing number of double bonds.     

neo‐Clerodane Diterpenoids from the Aerial Part of Scutellaria barbata

Three new neo‐clerodane diterpenoids, barbatellarines C–E ( 1 – 3 ), were isolated from the CHCl₃‐soluble fraction of the aerial part of Scutellaria barbata. Their chemical structures were elucidated by detailed analysis of NMR and MS data. Compounds 1 and 2 were C(13) epimers, which was confirmed by an NOE difference experiment and the NOESY spectrum. The relative configuration was determined on the basis of the ¹H‐NMR J‐value and NOE data, while the absolute configuration of the previously isolated analogue, barbatellarine B ( 4 ), as a representative member of the group, was assigned by CD analysis.     

The x-ray structural investigation of alkaloids I. Molecular structure and absolute configuration of (+)-cocculine

Summary An x-ray structural investigation of the alkaloid (+)-cocculine in the form of the hydrobromide has been performed. The bond lengths and valence angles are the usual ones. The conformations of the rings are: A — envelope⁴E; B — half-chair⁹T₅; C — half-chair¹⁰H₅. The absolute configuration 3R,5S has been established.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 395–400, May–June, 1975.     

Synthesis and Stereochemistry of 1<Emphasis Type="Italic">H</Emphasis>,5<Emphasis Type="Italic">H</Emphasis>-Naphtho[1,8-<Emphasis Type="Italic">ef</Emphasis>][1,3]dithiocine 2-Oxides

3-Substituted 1H,5H-naphtho[1,8-ef][1,3]dithiocines (R = H, Me, Ph, t-Bu) were oxidized with m-chloroperoxybenzoic acid to the corresponding 2-oxides having trans configuration (R ≠ H). According to the ¹H and ¹³C NMR data (including NOESY experiments), the disubstituted compounds at room temperature exist in a boat conformation with equatorial orientation of the substituent on C³ and oxygen atom on S². The compound with no substituent on C³ gives rise to a mixture of boat conformers with axial and equatorial sulfoxide oxygen atoms at a ratio of 83:17.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 7, 2005, pp. 1109–1112.Original Russian Text Copyright © 2005 by Kikilo, Khairutdinov, Shtyrlin, Klochkov, Klimovitskii.     

Characteristic frequencies in the infrared spectra of pyrazolines

Pyrazolines are characterized by valence vibrations at the following frequencies: C=N (1580–1627 cm^–1), H-C³=N (3040–3063 cm^–1), H-N (3270–3305 cm^–1) and CH₃-N (2780–2805 cm^–1). Lowering of the frequencies of the valence vibrations of C=N in pyrazolines, when compared with the magnitudes characteristic of alkyledene amines and oximes, is regarded as a consequence of coupling with the unshared electron pair of the neighboring nitrogen atom. By means of the IR spectra, it is possible to determine the position of the double bonds in the pyrazoline ring, to distinguish between pyrazolines substituted and nonsubstituted in positions 1 and 3, and to establish the presence of geminate (twin) methyl groups and methyl groups in position 1.