ASSIGNMENT OF NMR SIGNALS FOR CHLOROPRENE RUBBER BY TWO-DIMENSIONAL NMR SPECTROSCOPY

2013 ◽  
Vol 86 (2) ◽  
pp. 250-260
Author(s):  
Takayuki Saito ◽  
Seiichi Kawahara ◽  
Yoshito Ohtake
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
13C Nmr ◽  
Quantum Correlation ◽  
Multiple Bond ◽  
Multiple Quantum ◽  
Heteronuclear Multiple Bond Correlation ◽  
Nmr Spectrum ◽  
Chloroprene Rubber ◽  
Nmr Signals

ABSTRACT Various pulse techniques of NMR spectroscopy were applied to CR to assign some small signals in 13C and 1H NMR spectra for the rubber. First, the rubber was subjected to distortionless enhancement by polarization transfer and attached proton test. The small signals in the 13C NMR spectrum were assigned to secondary, tertiary, and quaternary carbons. Second, correlations between 13C and 1H were investigated by heteronuclear multiple quantum correlation, heteronuclear two bond correlation, and heteronuclear multiple bond correlation measurements to assign the small signals in the 13C NMR spectrum in detail. By using the resulting correlations between 13C and 1H, the small unassigned signals in 1H NMR spectrum were assigned to methylene and methine protons of the rubber.

Combined High-Resolution Solid-State 1H/13C NMR Spectroscopy and 1H NMR Relaxometry for the Characterization of Kerogen Thermal Maturation

2020 ◽  
Author(s):  
Francesco Panattoni ◽  
Jonathan Mitchell ◽  
Edmund J. Fordham ◽  
Ravinath Kausik ◽  
Clare P. Grey ◽  
...  
Keyword(s):  
Solid State ◽  
Nmr Spectroscopy ◽  
High Resolution ◽  
1H Nmr ◽  
13C Nmr ◽  
13C Nmr Spectroscopy ◽  
Thermal Maturation ◽  
Nmr Relaxometry ◽  
1H Nmr Relaxometry

scholarly journals One-Dimensional 13C NMR Is a Simple and Highly Quantitative Method for Enantiodiscrimination

Molecules ◽  
2018 ◽  
Vol 23 (7) ◽  
pp. 1785 ◽  
Author(s):  
Peter Lankhorst ◽  
Jozef van Rijn ◽  
Alexander Duchateau
Keyword(s):  
1H Nmr ◽  
13C Nmr ◽  
Quantitative Method ◽  
Enantiomeric Excess ◽  
Nmr Spectrum ◽  
One Dimensional ◽  
Nmr Method ◽  
Relative Standard ◽  
Excess Value ◽  
Chiral Solvating Agent

The discrimination of enantiomers of mandelonitrile by means of 1D 13C NMR and with the aid of the chiral solvating agent (S)-(+)-1-(9-anthryl)-2,2,2-trifluoroethanol (TFAE) is presented. 1H NMR fails for this specific compound because proton signals either overlap with the signals of the chiral solvating agent or do not show separation between the (S)-enantiomer and the (R)-enantiomer. The 13C NMR method is validated by preparing artificial mixtures of the (R)-enantiomer and the racemate, and it is shown that with only 4 mg of mandelonitrile a detection limit of the minor enantiomer of 0.5% is obtained, corresponding to an enantiomeric excess value of 99%. Furthermore, the method shows high linearity, and has a small relative standard deviation of only 0.3% for the minor enantiomer when the relative abundance of this enantiomer is 20%. Therefore, the 13C NMR method is highly suitable for quantitative enantiodiscrimination. It is discussed that 13C NMR is preferred over 1H NMR in many situations, not only in molecules with more than one chiral center, resulting in complex mixtures of many stereoisomers, but also in the case of molecules with overlapping multiplets in the 1H NMR spectrum, and in the case of molecules with many quaternary carbon atoms, and therefore less abundant protons.

scholarly journals IDENTIFICATION AND SEQUENCING BY NMR SPECTROSCOPY OF THE CARBOHYDRATE MOIETY IN A SAPONIN FROM Barringtonia asiatica

2010 ◽  
Vol 1 (3) ◽  
pp. 120-124
Author(s):  
Rymond J Rumampuk
Keyword(s):  
Nmr Spectroscopy ◽  
13C Nmr ◽  
Coupling Constants ◽  
Carbohydrate Moiety ◽  
Glycosidic Linkage ◽  
1H And 13C Nmr ◽  
Heteronuclear Correlation ◽  
Vicinal Coupling Constants ◽  
Nmr Signals

A trisaccharide chain in a saponin from the seeds of Barringtonia asiatica has been identified and sequenced as {[b-D-galactopyranosyl(1®3)- b-D-glucopyranosyl(1®2)]-b-D-glucuronopyranosyloxy} using a combination of homonuclear and heteronuclear correlation NMR spectroscopy. The 1H and 13C NMR signals of the sugar residues can be determined and distinguished from one other by use of the HMQC-TOCSY technique. Anomeric configurations were unambiguously assigned from the vicinal coupling constants 3JH-1,H-2 of the anomeric protons. Inter-glycosidic linkage assignments were elucidated using  HMBC.   Keyword: Barringtonia asiatica, carbohydrate, saponin, NMR

High-Resolution Latex-State 13C-NMR Spectroscopy for Natural Rubber Vulcanizates

2007 ◽  
Vol 80 (5) ◽  
pp. 751-761 ◽  
Author(s):  
Seiichi Kawahara ◽  
Jinta Ukawa ◽  
Junichiro Sakai ◽  
Yoshimasa Yamamoto ◽  
Yoshinobu Isono
Keyword(s):  
Nmr Spectroscopy ◽  
High Resolution ◽  
Natural Rubber ◽  
13C Nmr ◽  
Multiple Bond ◽  
Natural Rubber Latex ◽  
13C Nmr Spectroscopy ◽  
Rubber Latex ◽  
Aliphatic Carbon ◽  
Natural Rubber Vulcanizates

Abstract Crosslinking junctions of natural rubber vulcanizates were characterized by high-resolution latex-state 13C-NMR spectroscopy. Vulcanized natural rubber latex was prepared by two methods: i.e., vulcanization of the rubber latex and cryogenic crushing of a rubber sheet vulcanized on a hot press. High-resolution latex-state 13C-NMR spectroscopy was attained even after vulcanization of the rubber latex, as is evident from no background in spectrum and narrow half width of signals independent of vulcanization time. Small signals at 44 ppm and 57 ppm in the aliphatic carbon region were assigned by measurements of both Distortionless Enhancement by Polarization Transfer (DEPT) and Attached Proton Test (APT) to secondary and tertiary carbons of crosslinking points. The assignment was proved by high-resolution solution-state NMR spectroscopy of vulcanized liquid cis-1,4-polyisoprene as a model, in which DEPT, APT, 2-dimensional 1H-1H correlation (H-H COSY), 2-dimensional 1H-13C correlation (H-C COSY) and 2-dimensional heteronuclear multiple bond correlation (HMBC) measurements were applied.

scholarly journals Secondary metabolites of three endemic Centaurea L. species

2014 ◽  
Vol 79 (11) ◽  
pp. 1355-1362 ◽  
Author(s):  
Vele Tesevic ◽  
Ivana Aljancic ◽  
Slobodan Milosavljevic ◽  
Vlatka Vajs ◽  
Iris Djordjevic ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Nmr Spectroscopy ◽  
Secondary Metabolites ◽  
Sesquiterpene Lactone ◽  
1H Nmr ◽  
13C Nmr ◽  
1H Nmr Spectroscopy ◽  
13C Nmr Spectroscopy ◽  
Esi Ms ◽  
Aerial Parts

The aerial parts of three endemic Centaurea L. species, namely C. tomorosii Micevski, C. soskae Hayek and C. galicicae Micevski, afforded sesquiterpene lactone cnicin (1) and seven flavonoids: apigenin (2), isokaempferide (3), hispidulin (4), eupatorin (5), cirsimaritin (6), santaflavone (7) and salvigenin (8). The structures of the isolated compounds were determined by UV, 1H NMR and 13C NMR spectroscopy and HR-ESI-MS spectrometry. 1H NMR spectroscopy was used as a method for quantitative analysis of sesquiterpene lactone cnicin.

Organoboranes and tetraorganoborates studied by 11B and 13C NMR spectroscopy and DFT calculations

2015 ◽  
Vol 70 (6) ◽  
pp. 421-424 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Nmr Spectroscopy ◽  
Dft Calculations ◽  
13C Nmr ◽  
Quantum Chemical ◽  
13C Nmr Spectroscopy ◽  
Coupling Constants ◽  
Line Widths ◽  
Nmr Signals ◽  
C Nmr ◽  
Extract Information

AbstractCare should be taken on recording the sometimes elusive 13C NMR signals for boron-bonded carbon atoms, since it is easy to extract information about coupling constants 1J(13C,11B) by measuring the respective line widths of 13C(B-C) and 11B NMR signals. This information can be confirmed by quantum-chemical calculations [B3LYP (6-311+G(d,p) level of theory] of nJ(13C,11B) in organoboranes and tetraorganoborates. For the latter, the signs for n = 2, 3, 4 were experimentally determined.

scholarly journals CARACTERIZACIÓN DE UNA ESPIROLACTONA SESQUITERPÉNICA á-METILÉNICA OBTENIDA DE Ambrosia arborescens Miller Y EVALUACIÓN DE SU ACTIVIDAD BIOLÓGICA EN Tripanosoma cruzi

2014 ◽  
Vol 80 (2) ◽  
pp. 124-135
Author(s):  
Teresa Cano de Terrones
Keyword(s):  
Quantum Correlation ◽  
Multiple Bond ◽  
Correlation Spectroscopy ◽  
Single Quantum ◽  
Heteronuclear Multiple Bond Correlation ◽  
Heteronuclear Single Quantum Correlation ◽  
América Del Sur

Ambrosia arborescens Miller, denominada comúnmente "marco"; es una planta aromática, medicinal que se encuentra en América del Sur, mayormente en los Andes del Perú, en el Departamento de Arequipa. El estudio de los constituyentes químicos de la parte aérea de Ambrosia arborescens permitió obtener una espirolactona sesquiterpénica. Para su separación y aislamiento se utilizó métodos cromatográficos de columna, capa fina y cromatografía líquida de alta eficacia. La elucidación estructural se realizó a través de métodos espectroscópicos: resonancia magnética nuclear protónica (RMN-1H), del carbono-13 (RMN-13C), espectroscopía infrarroja (IR) y espectrometría de masas (EM). En la determinación de la estereoquímica y las conformaciones se empleó experimentos bidimensionales de espectroscopía: COSY (Correlation Spectroscopy), HSQC (Heteronuclear Single Quantum Correlation), HMBC (Heteronuclear Multiple Bond Correlation) y ROESY(Rotational nuclear Overhouser Effect Spectroscopy). Desde un punto de vista teórico, el análisis conformacional fue realizado a través de Mecánica Molecular empleando el programa MM2 de Hyperchem. La evaluación de la actividad antiparasitaria, in vitro, sobre Tripanosoma cruzi, mostró que a muy bajas concentraciones, el producto obtenido presenta actividad tripanocida.

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