scholarly journals Probing the Fluxional Bonding Nature of Rapid Cope rearrangements in Bullvalene C10H10 and Its Analogs C8H8, C9H10, and C8BH9

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Yuan-Yuan Ma ◽  
Miao Yan ◽  
Hai-Ru Li ◽  
Yan-Bo Wu ◽  
Xin-Xin Tian ◽  
...  
Keyword(s):  
Model Compound ◽  
Chemical Shifts ◽  
Transition States ◽  
Ground States ◽  
H Nmr ◽  
Natural Bond Orbitals ◽  
Compound C ◽  
Shielding Tensors ◽  
Cope Rearrangements ◽  
C Nmr

AbstractBullvalene C10H10 and its analogs semibullvalene C8H8, barbaralane C9H10, and 9-Borabarbaralane C8BH9 are prototypical fluxional molecules with rapid Cope rearrangements at finite temperatures. Detailed bonding analyses performed in this work reveal the existence of two fluxional π-bonds (2 2c-2e π → 2 3c-2e π → 2 2c-2e π) and one fluxional σ-bond (1 2c-2e σ → 1 4c-2e σ → 1 2c-2e σ) in their ground states and transition states, unveiling the universal π + σ double fluxional bonding nature of these fluctuating cage-like species. The highest occupied natural bond orbitals (HONBOs) turn out to be typical fluxional bonds dominating the dynamics of the systems. The 13C-NMR and 1H-NMR shielding tensors and chemical shifts of the model compound C8BH9 are computationally predicted to facilitate future experiments.

13C-NMR-Spektroskopie an polycyclischen Aromaten, II. Die 13C-NMR-Spektren von 1- und 2-Fluornaphthalin. Überprüfung der Signalzuordnung und Untersuchung der Substituenteneffekte auf die chemischen Verschiebungen / 13C NMR Spectroscopy of Polycyclic Aromatics, II. The 13C NMR Spectra of 1- and 2-Fluoronaphthalene. Reexamination of Signal Assignments and Investigation of Substituent Effects on Chemical Shifts

1975 ◽  
Vol 30 (9-10) ◽  
pp. 788-793 ◽  
Author(s):  
Ludger Ernst
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Double Resonance ◽  
Substituent Effects ◽  
13C Nmr Spectroscopy ◽  
Polycyclic Aromatics ◽  
H Nmr ◽  
Iterative Analysis ◽  
C Nmr

During a reinvestigation of the 13C NMR spectra of 1-fluoronaphthalene (1) and of 2-fluoronaphthalene (2) at 20 and 25.16 MHz, uncertainties that existed in the literature about signal assignments for 1 could be cleared. In the spectral analyses for 2 given so far, five out of ten signals were incorrectly assigned. The corrected assignment is supported by extensive 13C{1H} double resonance experiments, by recording of proton-coupled 13C and 13C{19F} spectra and by off-resonance 13C{1H} noise-decoupling. The results show a strong + M-effect of the fluorine substituents on 13C chemical shifts similar to the effects of OH and OCH3 groups. 1H NMR spectra of 1 and 2 could be partially assigned by decoupling of the 19F resonances and by iterative analysis.

Neue Untersuchung über Inhaltsstoffe aus Aloe-und Rhamnus-Arten, XV [1] Homonataloin A und B aus Aloe lateritia: Reindarstellung, Konstitutions-und Konfigurationsaufklärung der Diastereomeren / A New Investigation on Constituents of Aloe and Rhamnus Species, XV [1] Hom onataloins A and B from Aloe lateritia: Isolation, Structure and Configurational Determ ination of the Diastereomers

1991 ◽  
Vol 46 (3-4) ◽  
pp. 177-182 ◽  
Author(s):  
Hans-W. Rauwald ◽  
Deo-D. Niyonzima
Keyword(s):  
Chemical Shifts ◽  
Optical Rotation ◽  
Coupling Constants ◽  
Cd Spectra ◽  
Large Coupling ◽  
H Nmr ◽  
Leaf Exudate ◽  
Hydroxyl Protons ◽  
Nmr Signals ◽  
C Nmr

From the leaf exudate of Aloe lateritia ENGLER the C-glucosyl com pounds homonataloin, aloeresin A and aloesin (synon. aloeresin B) were isolated together with the anthraquinone nataloeem odin-8-methylether and spectroscopically identified. Hom onataloin, widely distributed in Aloe species, was separated into homonataloin A and B by combined TLC and DCCC. In their 1 D and 2D 1H NMR spectra only the shifts of the 2′-hydroxyl protons of both glucosyl residues differ significantly, indicative of 10 S (A) resp. 10 S (B) configurations. In both com pounds the anthrone is in β-position of the D-glucopyranosyl, as determined by the large coupling constants of the anomeric protons. The 13C NMR signals are unambiguously assigned by the use of DEPT, APT and gated-decoupling methods. Only the chemical shifts of C -11 and C -14 show significant differences between both diastereomers due to the adjacent 2′-sugar hydroxyls. The two homonataloins differ mostly in optical rotation and circulardichroism due to different configurations at C - 10 of the anthrone part. The absolute configurations of the diastereomers are determined by correlation of their CD spectra with the CD spectra of the structural analogues 7-hydroxyaloins A and B, which shows that hom onataloin A is the 10 S, 1′S-compound and that homonataloin B has 10 R, 1′S-configuration.

Synthesis and characterization of several series of 4-acyl-1-[2-aryl-1-diazenyl]piperazines

2014 ◽  
Vol 92 (9) ◽  
pp. 838-848 ◽  
Author(s):  
Vanessa Renee Little ◽  
Keith Vaughan
Keyword(s):  
High Resolution ◽  
Ir Spectroscopy ◽  
Chemical Shifts ◽  
Synthesis And Characterization ◽  
Model Compounds ◽  
Primary Aromatic Amine ◽  
Piperazine Ring ◽  
H Nmr ◽  
C Nmr

Five series of a novel class of 4-acyl-1-[2-aryl-1-diazenyl]piperazines have been synthesized and characterized: the 4-acetyl-1-[2-aryl-1-diazenyl]piperazines [series 1]; the 4-cyclohexylcarbonyl-1-[2-aryl-1-diazenyl]piperazines [series 2]; the 4-benzoyl-1-[2-aryl-1-diazenyl]piperazines [series 3]; the benzyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates [series 4]; and the t-butyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates [series 5]. The compounds were synthesized by diazotization of a primary aromatic amine and subsequent coupling to an appropriate secondary amine: 1-acetylpiperazine [series 1]; 1-(cyclohexylcarbonyl)-piperaizine [series 2]; 1-benzoylpiperazine [series 3]; benzyl 1-piperazinecarboxylate [series 4]; and t-butyl piperazine-1-carboxylate (1-BOC-piperazine) [series 5]. The compounds of series 1–5 were characterized by 1H NMR, 13C NMR, high-resolution MS and IR spectroscopy. The model compounds 1,4-di[2-aryl-1-diazenyl]piperazines, and ethyl 4-[2-aryl-1-diazenyl]-1-piperazinecarboxylates were used to facilitate the assignment of the chemical shifts specific to the piperazine ring carbons. HSQC spectra of select compounds established the correlation between proton and carbon resonance signals.

(3E)-5-Hydroxy-3-[5-(hydroxymethyl)furan-2-ylmethylene]-1-benzofuran-2(3H)-one

2007 ◽  
Vol 63 (11) ◽  
pp. o4354-o4354
Author(s):  
Hong-Yan Ma ◽  
Ji Shi ◽  
Chang-Hong Wang ◽  
Zheng-Tao Wang
Keyword(s):  
Hydrogen Bonds ◽  
Spectroscopic Data ◽  
Furan Ring ◽  
Crystallographic Analysis ◽  
Relative Configuration ◽  
X Ray ◽  
H Nmr ◽  
Compound C ◽  
A Chain ◽  
C Nmr

The title compound, C14H10O5, was isolated from Senecio cannabifolius Less var. integrifolius aqueous extract. The structure was elucidated on the basis of spectroscopic data, including MS, 1H NMR and 13C NMR, and the relative configuration was confirmed by X-ray crystallographic analysis. The benzofuran ring is almost coplanar with the furan ring [dihedral angle = 10.47 (15)°]. A chain is formed through supramolecular R 2 2(10) synthons and three-centre hydrogen bonds.

Polar effects on 13C NMR chemical shifts and rotational barriers of amides. A dual substituent parameters analysis of N,N-dimethyl-3-(5-substituted-2-furyl)-acrylamides

1987 ◽  
Vol 52 (2) ◽  
pp. 409-424 ◽  
Author(s):  
Zdeněk Friedl ◽  
Stanislav Böhm ◽  
Igor Goljer ◽  
Anna Piklerová ◽  
Daniela Poórová ◽  
...  
Keyword(s):  
Substituent Effect ◽  
Chemical Shifts ◽  
Polar Effect ◽  
Dominant Factor ◽  
Side Chain ◽  
Nmr Chemical Shifts ◽  
Resonance Effects ◽  
H Nmr ◽  
Reverse Substituent Effect ◽  
C Nmr

13C NMR chemical shifts were measured for sixteen N,N-dimethyl-3-(5-substituted-2-furyl)-acrylamides in CDCl3 at 21 °C; the barriers of rotation about the C-N bond ΔGc° were determined by using the 1H NMR coalescence method, and the positions of the IR bands of the ν(C=O) stretching vibrations were measured. The dual substituent parameters (DSP) analysis of the 13C NMR chemical shifts for atoms of the vinylcarboxamide side chain -C(3)H=C(2)H-C(1)=O(-N) gives evidence that the chemical shifts for the C-1 and C-3 atoms are controlled primarily by polar effects (δ(C-3) = -3.12σI - 1.03σR0; λ = ρI/ρR = 3.0), which exert a reverse substituent effect on these atoms. Similarly, the DSP analysis of the ΔGc° and ν(C=O) data shows that the dominant factor of the total substituent effect is the polar effect (λ = 1.95 and 1.70, respectively). A confrontation of the results of the DSP analysis with the CNDO/2 calculated electron densities at the corresponding atoms demonstrates that the reactivity of the entire vinylcarboxamide side chain can be well explained in terms of a combination of the polar effect (π-electron polarization) with resonance effects.

Part II. Conformational analysis of 4- and 5-substituted thiazolidine-2-thiones

1980 ◽  
Vol 58 (6) ◽  
pp. 604-616 ◽  
Author(s):  
F. Chanon ◽  
M. Rajzmann ◽  
M. Chanon ◽  
J. Metzger ◽  
G. Pouzard ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Alkyl Substituent ◽  
Chair Conformation ◽  
Equatorial Orientation ◽  
Anomeric Effect ◽  
H Nmr ◽  
Transannular Interaction ◽  
Conformational Properties ◽  
Out Of Plane ◽  
C Nmr

Variation of the conformational properties in a series of 4-R-thiazolidine-2-thiones (4-R = Me, Et, iPr, tBu, OH) and 5-R-thiazolidine-2-thiones (5-R = Me, Et, iPr, tBu) is deduced from 1H nmr (Karplus 3J, chemical shifts, 2J44′, 2J55′) 13C nmr data and CNDO-2 calculations. In the absence of any transannular interaction, vicinal constraints and van der Waals requirements of the substituents control the conformational equilibrium. The pseudo-axial arrangement is favoured when 4-R = Me, while the substituent presents no preferential orientation when 5-R = Me. As the size of the 5-alkyl and the 4-alkyl substituent increases, its pseudo-equatorial orientation and the predominance of the C4C5 out-of-plane half-chair conformation are favoured. This does not lead to conformational exclusivity even when 4-R or 5-R is tBu. When 4-R is hydroxy, there is a definite pseudo-axial conformation (anomeric effect) and the ring preference is of the C4 out-of-plane type.

Liquefaction Mechanism of β-O-4 Lignin Model Compound in the Presence of Phenol under Acid Catalysis. Part 1. Identification of the Reaction Products

Holzforschung ◽  
2001 ◽  
Vol 55 (6) ◽  
pp. 617-624 ◽  
Author(s):  
L. Lin ◽  
Y. Yao ◽  
N. Shiraishi
Keyword(s):  
High Performance ◽  
Model Compound ◽  
Structural Characteristics ◽  
Main Reaction ◽  
Reaction Products ◽  
Lignin Model Compound ◽  
H Nmr ◽  
Lignin Model ◽  
Oxalic Acids ◽  
C Nmr

Summary Guaiacylglycerol-β-guaiacyl ether (GG) was used as a lignin model compound to study the liquefaction reaction mechanism of lignin in the presence of phenol under the catalysis of several typical acids such as sulfuric, phosphoric and oxalic acids. The reaction products were isolated by silicagel column chromatography and high performance liquid chromatography (HPLC). The structures of the obtained compounds were identified by means of GC-MS, 1H-NMR, 13C-NMR, 1H-1H COSY, HMBC and HMQC. As a result, about 30 compounds were obtained as the main reaction products. It was found that their structural characteristics were significantly different from those yielded at the non-catalyzed liquefaction (Lin et al. 1997a), and independent on the acid species. The dominant products were guaiacylglycerol-α-phenyl-β-guaiacyl ethers, followed by guaiacol, triphenylethanes, diphenylmethanes, benzocyclobutanes and phenylcoumarans. The structural characteristics and yields of these main reaction products indicated that condensation between phenol and GG in its C-α and further cleavages in both the β-O-4 linkage and Cβ–Cγ bonding could be the dominant reaction pathways.

A new ent-kaurane from the root extract of Chiococcaalba

1997 ◽  
Vol 75 (6) ◽  
pp. 801-804 ◽  
Author(s):  
Rocío Borges-Argáez ◽  
Leticia Medina-Baizabál ◽  
Filogonio May-Pat ◽  
Luis M. Peña-Rodríguez
Keyword(s):  
Antimicrobial Activity ◽  
Medicinal Plants ◽  
Crude Extract ◽  
Chemical Shifts ◽  
Root Extract ◽  
Spectroscopic Methods ◽  
Chemical Transformations ◽  
Bioactive Metabolite ◽  
H Nmr ◽  
C Nmr

A bioassay-guided purification of the methanolic crude extract obtained from the roots of Chiococcaalba (L.) Hitchc. resulted in the isolation of a new, bioactive, metabolite identified as ent-17-hydroxy-16α-kauran-3-one (1). Elucidation of the new structure was based on analyses of the results obtained from various spectroscopic methods (IR, MS, 1H NMR, and 13C NMR) and chemical transformations. The stereochemistry at C16 was assigned by comparing both the proton and carbon chemical shifts of C17 with those reported in the literature. The new kaurane showed weak antimicrobial activity when tested against Staphylococcusaureus. Keywords: medicinal plants, Chiococcaalba, Rubiaceae, kaurane, diterpene, antimicrobial.

13C and 1H NMR spectra of all methyl O-benzoyl-β-D-xylopyranosides. nonadditivity of acylation effects on 13C chemical shifts in deutoriochloroform solutions

1983 ◽  
Vol 48 (3) ◽  
pp. 877-888 ◽  
Author(s):  
Eva Petráková ◽  
Jan Schraml
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Conformational Heterogeneity ◽  
Additivity Rule ◽  
Homonuclear Decoupling ◽  
First Order ◽  
H Nmr ◽  
C Nmr

All methyl O-benzoyl-β-D-xylopyranosides have been prepared and their 1H and 13C NMR spectra measured in deuteriochloroform solutions. The 1H NMR spectra were analysed to the first order and assigned with the aid of homonuclear decoupling. The 13C chemical shifts were assigned through heteronuclear selective decouling experiments. Some of the 13C chemical shifts observed in di- and tri-O-benzoyl derivatives differ considerably from those calculated according to the direct additivity rule from the shifts in the mono derivatives. It is shown that the nonadditivity is due to a conformational heterogeneity of the series of investigated compounds dissolved in deuteriochloroform. The heterogeneity is evidenced by the vicinal 1H-1H coupling constants and by 13 chemical shifts of C(1) methoxyl carbon atoms.

scholarly journals IR and NMR Spectral Studies of Some 4-(6-methoxy-2-naphthyl)-5,6-dihydro-6-(Substituted Phenyl)-4H-1,3-Oxazine-2-Amines: Assessment of Substituent

2013 ◽  
Vol 23 ◽  
pp. 109-116
Author(s):  
Ganesamoorthy Thirunarayanan
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Statistical Analyses ◽  
Spectral Studies ◽  
Ir And Nmr Spectra ◽  
Effect Of Substituents ◽  
H Nmr ◽  
Substituent Constants ◽  
C Nmr

A series containing thirteen title compounds were synthesized and recorded IR and NMR spectra. The infrared νNH, C=N(cm-1)stretches, 1H NMR δNH, 13C NMR δC=N(ppm) chemical shifts of synthesized oxazine amines were assigned and correlated with Hammett substituent constants, F and R parameters. From the results of statistical analyses, the effect of substituents on the above spectral frequencies can be discussed.

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