scholarly journals Differentiation between 6- and 7-Membered Rings Based on Theoretical Calculation of NMR Parameters

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Karel D. Klika
Keyword(s):  
Dft Calculation ◽  
Chemical Shifts ◽  
Membered Ring ◽  
Coupling Constants ◽  
Scalar Coupling ◽  
Ring Size ◽  
Broad Application ◽  
Nmr Parameters ◽  
Difficult Cases

The determination of ring size can vary from simple to complex, but the process in difficult cases can be advantageously augmented by DFT calculation of NMR parameters such as the chemical shifts of (), (), and other nuclei as well as pertinent spin-spin (scalar) coupling constants, for example, those between protons (). Differentiation between 6- and 7-membered ring formation in the case of 3,4-dihydro-2H-3-hydroxymethyl-1,4-benzoxazine and 2,3,4,5-tetrahydro-1,5-benzoxazepine-3-ol was evaluated with a view to not only affecting 6- versus 7-membered ring differentiation generally for cases on hand, but also in the case of literature reports where the assigned structures may be in doubt. Thus, the main focus was on the usually reported NMR parameters of , , and and wherein the analysis was found to be highly successful, particularly for , and thus potentially amenable for broad application.

Gradient-Enhanced Inverse-Detected NMR Techniquesfor Determination of 1H-15N Coupling Constants in 2,2-Dimethylpenta-3,4-dienal Derivatives

1997 ◽  
Vol 62 (11) ◽  
pp. 1747-1753 ◽  
Author(s):  
Radek Marek
Keyword(s):  
Double Bond ◽  
Chemical Shifts ◽  
Multiple Bond ◽  
Coupling Constants ◽  
Single Quantum ◽  
Nmr Techniques ◽  
Phase Sensitive ◽  
Heteronuclear Coupling

Determination of 15N chemical shifts and heteronuclear coupling constants of substituted 2,2-dimethylpenta-3,4-dienal hydrazones is presented. The chemical shifts were determined by gradient-enhanced inverse-detected NMR techniques and 1H-15N coupling constants were extracted from phase-sensitive gradient-enhanced single-quantum multiple bond correlation experiments. Stereospecific behaviour of the coupling constants 2J(1H,15N) and 1J(1H,13C) has been used to determine the configuration on a C=N double bond. The above-mentioned compounds exist predominantly as E isomers in deuteriochloroform.

Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

Carbon magnetic resonance studies of some phenyl, furyl and thienyl organometallics. Some comments on carbon-metal scalar coupling

1974 ◽  
Vol 27 (2) ◽  
pp. 417 ◽  
Author(s):  
D Doddrell ◽  
KG Lewis ◽  
CE Mulquiney ◽  
W Adcock ◽  
W Kitching ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Scalar Coupling ◽  
Coupling Constant ◽  
Aryl Substituent ◽  
Magnetic Resonance Studies ◽  
Thienyl Group ◽  
13C Chemical Shift

13C chemical shift variations within a series of phenyl, furyl and thienyl Group IVB organometallics appear to be best understood in terms of the usual alkyl and aryl substituent effects on 13C chemical shifts and not variations in dπ ?pπ metal-aryl interactions. Large changes in 13C-metal scalar coupling constants have been observed suggesting that other factors besides the s-character of the carbon-metal bond is responsible in determining the coupling constant.

scholarly journals Determination of unresolved heteronuclear scalar coupling constants by J(up)-HSQMBC

2016 ◽  
Vol 268 ◽  
pp. 88-94 ◽  
Author(s):  
Simon Glanzer ◽  
Olaf Kunert ◽  
Klaus Zangger
Keyword(s):  
Coupling Constants ◽  
Scalar Coupling

The Ring Size Influence on 29Si N.M.R. Chemical Shifts of Some Spirocyclic Tetra- and Penta-coordinate Diolato Silicates

1995 ◽  
Vol 48 (1) ◽  
pp. 93 ◽  
Author(s):  
T Kemmitt ◽  
NB Milestone
Keyword(s):  
Chemical Shift ◽  
Coordination Number ◽  
Chemical Shifts ◽  
Membered Ring ◽  
Ring Size ◽  
Species Being

A series of tetracoordinate spirocyclic silicates has been prepared from the reaction of a range of diols with tetraethoxysilane, Si ( OEt )4. The silicates can be converted into anionic pentacoordinate silicates by reaction with KOBut/18-crown-6 in toluene. Alternatively, the pentacoordinate spirocycles can be prepared directly without prior preparation of a tetracoordinate spiro silicate. 29Si n.m.r. studies have demonstrated that the chemical shifts are sensitive to both coordination number and ring size. Ring contributions to the 29Si chemical shifts are apparent for the five- membered ring spiro silicates, those for the pentcoordinate species being less than those for the tetracoordinate species. Acyclic and six- membered ring spiro silicates are virtually indistinguishable by 29Si n.m.r. spectroscopy, which demonstrates that no ring contribution to the chemical shift is apparent for this ring size.

Beiträge zur Chemie des Phosphors, 621 Zur Frage des 31P-kernresonanzspektroskopischen Nachweises von monomerem und dimerem Phenylphosphor und der Ringgröße von Organyl-cyclophosphanen.

1976 ◽  
Vol 31 (5) ◽  
pp. 558-564 ◽  
Author(s):  
Marianne Baudler ◽  
Burkhard Carlsohn ◽  
Wolfgang Böhm ◽  
Goswin Reuschenbach
Keyword(s):  
Spectroscopic Investigation ◽  
Chemical Shifts ◽  
High Yield ◽  
Ring Size ◽  
Nmr Spectrum ◽  
Spectroscopic Evidence ◽  
Nmr Parameters ◽  
Similar Chemical ◽  
First Time ◽  
Related Compounds

The weak resonances at + 22 and + 49 ppm appearing in the 31P NMR spectrum of melts or solutions of (PPh)5 that have been attributed previously in the literature to “dimeric” and “monomeric phenylphosphorus” are caused by (PPh)6 and (PPh)4, respectively. This was proved by comparison with the 31P NMR parameters of related compounds and by 31P NMR spectroscopic investigation of authentic samples of (PPh)6 and (PPh)4, the latter of which was prepared in high yield from (Me3Si)PhP–PPh–PPh(SiMe3) and PhPCl2. (PEt)4 and mixed-substituted phenyl-ethyl-cyclotetraphosphanes exhibit similar chemical shifts as (PPh)4, corresponding mixed-substituted cyclohexaphosphanes have similar chemical shifts as (PPh)6. Generally, cyclophosphanes establish an equilibrium between (PR)n-species of different ring-size. Probably, the ring-interconversion proceeds via a multi-center mechanism. No 31P NMR spectroscopic evidence for the existence of free PPh or P2Ph2 under the conditions described could be detected. On thermolysis of (PEt)4 the existence of (PEt)3 was proved for the first time.

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