NMR studies. XXL. Stereochemistry of 9-alkyl-9,10-dihydroanthracenes. Conformation by nuclear Overhauser enhancements and long-range coupling constants

1970 ◽  
Vol 92 (20) ◽  
pp. 5912-5916 ◽  
Author(s):  
Allan W. Brinkmann ◽  
M. Gordon ◽  
Ronald G. Harvey ◽  
Peter W. Rabideau ◽  
J. B. Stothers ◽  
...  
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Nmr Studies ◽  
Nuclear Overhauser

1H and 13C NMR studies of the conformational mobility of 1,2-dimethoxybenzene in solution

1990 ◽  
Vol 68 (8) ◽  
pp. 1393-1398 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Alberta Lemire ◽  
Glenn H. Penner
Keyword(s):  
Long Range ◽  
Conformational Mobility ◽  
Coupling Constants ◽  
Nmr Studies ◽  
Ambient Temperatures ◽  
Average Value ◽  
H Nmr ◽  
Methoxy Groups ◽  
Internal Mobility ◽  
C Nmr

1H NMR and 13C NMR spectral data are presented for 1,2-dimethoxybenzene-α,α′-13C, as well as for a number of other anisole derivatives. For the title molecule, the coupling constants between the 13C nucleus in the side chain and the para ring proton or 13C nucleus in the benzene ring show that the expectation value of sin2 θ is very near 0.2 at 300 K, where θ is the angle by which the methoxy groups twist out of the aromatic plane. This value of [Formula: see text] is much larger than that of 0.05 for anisole in solution, emphasizing the greater conformational mobility of the methoxy groups in 1,2-dimethoxybenzene (DMB). Long-range coupling constants between the methyl and ring protons in DMB are also discussed and compared with those in anisole and some of its derivatives. The preponderance of conformations with large values of θ, thought to occur in the vapor, disappears in solution at ambient temperatures. Under these conditions, the molecule is perhaps best described as preferring a planar conformation in which, however, the methoxy groups undergo excursions in θ whose average value is near 25°. Keywords: 1,2-dimethoxybenzene, conformational behaviour, internal mobility, long-range coupling constants, 1H and 13C NMR.

Long-range proton coupling constants and molecular orbital calculations as indicators of conformational populations of benzene-1,2- and -1,3-dicarbaldehydes

1986 ◽  
Vol 64 (1) ◽  
pp. 158-163 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Rudy Sebastian ◽  
Craig S. Takeuchi
Keyword(s):  
Dipole Moment ◽  
Carbon Tetrachloride ◽  
Molecular Orbital ◽  
Long Range ◽  
Benzene Solution ◽  
Geometry Optimization ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Trans Form ◽  
Nmr Studies

The 1H nmr spectra of the benzene-1,2- and -1,3-dicarbaldehydes in carbon tetrachloride, benzene-d6, and acetone-d6 solutions at 300 K are analyzed. The stereospecific long-range couplings over five formal bonds between the sidechain and ring protons show that the 1,2 isomer exists as an 87:13 mixture of the cis–trans and trans–trans conformers in carbon tetrachloride. These populations are insensitive to solvent. Molecular orbital calculations utilizing extensive geometry optimization procedures imply that the cis–cis form, with proximate C=O bonds, is indeed of negligible significance as assumed in obtaining the populations of the other forms. Further calculations define a pathway of relatively low energy for interconversion of the two abundant forms, in agreement with dynamic nmr studies. For the 1,3 isomer the long-range couplings provide a check of the conformer populations deduced from dipole moment and 13C nmr studies. For example, if the cis–trans form is 70% abundant, as deduced from the dipole moment in benzene solution, then the long-range couplings imply that the population of the cis–cis conformer is insignificant.

1H NMR studies of [N-MeAib1, Tyr(Me)4]ANGII and [N-MeAib1, Tyr(Me)4, Ile8]ANGII in dimethylsulfoxide by nuclear Overhauser effect (NOE) enhancement spectroscopy: cis-trans Isomerism of the His-Pro bond

1990 ◽  
Vol 55 (4) ◽  
pp. 1106-1111 ◽  
Author(s):  
John Matsoukas ◽  
Paul Cordopatis ◽  
Raghav Yamdagni ◽  
Graham J. Moore
Keyword(s):  
1H Nmr ◽  
Nuclear Overhauser Effect ◽  
Nmr Studies ◽  
Restricted Rotation ◽  
Overhauser Effect ◽  
Major Isomer ◽  
Conformational Properties ◽  
Nuclear Overhauser

The conformational properties of the Sarmesin analogues [N-MeAib1, Tyr(Me)4]ANGII and [N-MeAib1, Tyr(Me)4, Ile8]ANGII in hexadeutero-dimethysulfoxide were investigated by Nuclear Overhauser Effect (NOE) Enhancement Studies. Cis-trans isomers (ratio 1 : 6) due to restricted rotation of the His-Pro bond were observed. Interresidue interactions between the His Cα proton and the two Pro Cδ protons revealed that the major isomer was the trans.

How to measure long-range proton-carbon coupling constants from 1 H-selective HSQMBC experiments

2019 ◽  
Vol 58 (5) ◽  
pp. 363-375 ◽  
Author(s):  
Josep Saurí ◽  
Pau Nolis ◽  
Teodor Parella
Keyword(s):  
Long Range ◽  
Coupling Constants

scholarly journals NMR solution conformation of heparin-derived tetrasaccharide

1996 ◽  
Vol 318 (1) ◽  
pp. 93-102 ◽  
Author(s):  
Dmitri MIKHAILOV ◽  
Kevin H. MAYO ◽  
Ioncho R. VLAHOV ◽  
Toshihiko TOIDA ◽  
Azra PERVIN ◽  
...  
Keyword(s):  
Chair Conformation ◽  
Coupling Constants ◽  
Solution Conformation ◽  
1H And 13C Nmr ◽  
Small Deviations ◽  
J Coupling Constants ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Dynamics Simulations ◽  
Ring Conformations

The solution conformation of the homogeneous, heparin-derived tetrasaccharide ΔUA2S(1 → 4)-α-d-GlcNpS6S(1 → 4)-α-l-IdoAp2S(1 → 4)-α-d-GlcNpS6S (residues A, B, C and D respectively, where IdoA is iduronic acid) has been investigated by using 1H- and 13C-NMR. Ring conformations have been defined by J-coupling constants and inter-proton nuclear Overhauser effects (NOEs), and the orientation of one ring with respect to the other has been defined by inter-ring NOEs. NOE-based conformational modelling has been done by using the iterative relaxation matrix approach (IRMA), restrained molecular dynamics simulations and energy minimization to refine structures and to distinguish between minor structural differences and equilibria between various ring forms. Both glucosamine residues B and D are in the 4C1 chair conformation. The 6-O-sulphate group is oriented in the gauche–trans configuration in the D ring, whereas in the B ring the gauche–gauche rotomer predominates. Uronate (A) and iduronate (C) residues are mostly represented by 1H2 and 2S0 twisted boat forms, respectively, with small deviations in expected coupling constants and NOEs suggesting minor contributions from other A and C ring conformations.

Sign in / Sign up

Export Citation Format

Share Document