Observation of buttressing effect and hindered rotation about C(sp2)—C(sp2) single bond in styrenes coordinated to a ruthenium cation, Cp(diphosphine)Ru+

1996 ◽  
Vol 74 (11) ◽  
pp. 1936-1944
Author(s):  
Kenzo Ohkita ◽  
Hideo Asano ◽  
Hideo Kurosawa ◽  
Toshikazu Hirao ◽  
Yohko Miyaji ◽  
...  
Keyword(s):  
Variable Temperature ◽  
Phenyl Group ◽  
Shielding Effect ◽  
Single Bond ◽  
Conformational Isomerism ◽  
Nmr Studies ◽  
Hindered Rotation ◽  
Restricted Rotation ◽  
Conformational Isomers ◽  
Dominant Isomer

Complexes of (η5-cyclopentadienyl)(bis(di-p-tolylphosphino)ethane)ruthenium(II) cation with some styrenes containing meta or para substituants were prepared and their NMR spectra examined in detail. Variable-temperature NMR studies on the unsubstituted and para-substituted styrene analogues demonstrated occurrence of a restricted rotation about the C(sp2)—C(sp2) single bond of the styrenes where one of the ortho hydrogens of the styrene phenyl group receives a very large diamagnetic shielding effect by one of the phosphine tolyl groups. Similar studies on the meta-substituted styrene complexes showed existence of two unequally populated conformational isomers arising from the similar restricted rotation where the meta substituent in the dominant isomer was placed further away from the C=C group. The origin of such conformational isomerism was deduced to be the buttressing effect of the meta substituent transmitted via the ortho-hydrogen atom. Key words: buttressing effect, hindered rotation, Ru–styrene complex.

scholarly journals The syntheses and NMR studies of hexadeca- and octaneopentoxyphthalocyanines

2002 ◽  
Vol 80 (2) ◽  
pp. 141-147 ◽  
Author(s):  
Namrta Bhardwaj ◽  
John Andraos ◽  
Clifford C Leznoff
Keyword(s):  
Nmr Spectra ◽  
Variable Temperature ◽  
Nickel Chloride ◽  
Nmr Studies ◽  
Restricted Rotation ◽  
H Nmr

The syntheses of 3,6-dineopentoxyphthalonitrile and 3,4,5,6-tetraneopentoxyphthalonitrile are described. Condensation of these phthalonitriles with nickel chloride in N,N-dimethylaminoethanol yielded 1,4,8,11,15,18,22,25-octaneopentoxyphthalocyaninato nickel(II) (3) and 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecaneopentoxyphthalocyaninato nickel(II) (7). The 1H NMR spectra of these phthalocyanines and the related 2,3,9,10,16,17,23,24-octaneopentoxyphthalocyaninato nickel(II) (8) at temperatures from 205 to 330 K in toluene-d8 exhibited various degrees of restriction of rotation of the neopentoxy groups. Compound 7 exhibited a single atropisomer at 235 K.Key words: neopentoxy substituted phthalocyanines, variable temperature NMR, restricted rotation.

1H NMR Conformational Studies in Water of Angiotensin II Analogues Modified at the N- and C-Termini: Interactions of the Aromatic Side Chains and Folding of the N-Terminal Domain

1994 ◽  
Vol 59 (11) ◽  
pp. 2523-2532 ◽  
Author(s):  
John Hondrelis ◽  
John Matsoukas ◽  
George Agelis ◽  
Paul Cordopatis ◽  
Ning Zhou ◽  
...  
Keyword(s):  
Shielding Effect ◽  
Resonance Spectroscopy ◽  
Nmr Studies ◽  
Previous Suggestion ◽  
Aminoisobutyric Acid ◽  
H Nmr ◽  
Neutral Ph ◽  
Angiotensin Ii Analogues ◽  
Proton Resonances ◽  
Cosy Nmr

The conformation of [Sar1]angiotensin II in water at neutral pH has been examined by proton magnetic resonance spectroscopy at 400 MHz and in particular by comparing its 1H NMR spectral data with those of analogues modified at positions 1,4 and 6, namely [Sar1,Cha8]ANGII, [Des Asp1,Cha8]ANGII, [Aib1,Tyr(Me)4]ANGII, [Aib1,Tyr(Me)4,Ile8]ANGII, [N-MeAib1,Tyr(Me)4]ANGII, [N-MeAib1,Tyr(Me)4,Ile8]ANGII, ANGIII and [Sar1,Ile8]ANGII. Assignment of all proton resonances in these analogues was made possible by 2D COSY NMR experiments. The H-2 and H-4 protons for the histidine ring in [Sar1]ANGII, ANGII and ANGIII were shielded compared with the same protons in [Sar1,Ile8]ANGII, [Sar1,Cha8]ANGII and [Des Asp1,Cha8]ANGII; this shielding effect was not disturbed upon methylation of the tyrosine hydroxyl and/or replacement of residue 1 (sarcosine or aspartic acid) with aminoisobutyric acid (Aib) or N-methyl aminoisobutyric acid (N-MeAib). These data are consistent with our previous suggestion based on NMR studies in neutral DMSO that a characteristic folded conformation for ANGII previously observed in non-polar solvents can also be detected in water at neutral pH, but to a lesser degree.

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.

NMR Studies of Hindered Rotation in Cubic KCN

1968 ◽  
Vol 49 (10) ◽  
pp. 4721-4722 ◽  
Author(s):  
Eiichi Fukushima
Keyword(s):  
Nmr Studies ◽  
Hindered Rotation

Chiral "basket handle" binaphthyl porphyrins: synthesis, catalytic epoxidation and NMR conformational studies

2010 ◽  
Vol 14 (07) ◽  
pp. 646-659 ◽  
Author(s):  
Eric Rose ◽  
Emma Gallo ◽  
Nicolas Raoul ◽  
Léa Bouché ◽  
Ariane Pille ◽  
...  
Keyword(s):  
Time Scale ◽  
Room Temperature ◽  
Conformational Equilibrium ◽  
Variable Temperature ◽  
Conformational Exchange ◽  
Iron Catalysts ◽  
Nmr Studies ◽  
Conformational Studies ◽  
H Nmr ◽  
Catalytic Epoxidation

Three "basket handle" porphyrins have been prepared by condensation of tetrakis-(α,β,α,β-2-aminophenyl)porphyrin atropoisomer with 1,1′-binaphthyl, 2,2′-dimethoxy, -3,3′-dicarbonylchloride, -3,3′-diacetylchloride and -3,3′-dipropanoylchloride. The epoxidation of styrene with the three iron catalysts, obtained after metalation of the free porphyrins, occurs with good yields and moderate ee up to 54%. These porphyrins showed unexpected conformational differences, as revealed by NMR spectroscopy. In particular, variable temperature NMR studies showed that the methoxy group in one of them undergoes intermediate conformational exchange on the 1H NMR time scale at room temperature. Lowering the temperature to -50 °C revealed the presence of four states in slow exchange on the NMR time scale. These results evidence a dynamic conformational equilibrium of the binaphthyl handles that adopt different, asymmetric positions with respect to the porphyrin plane.

scholarly journals Variable temperature 1H NMR studies on Grubbs catalysts

2008 ◽  
Vol 693 (7) ◽  
pp. 1252-1260 ◽  
Author(s):  
Margaret M. Gallagher ◽  
A. Denise Rooney ◽  
John J. Rooney
Keyword(s):  
1H Nmr ◽  
Variable Temperature ◽  
Nmr Studies ◽  
Grubbs Catalysts

13C Dynamic NMR Studies on Restricted Rotation about C-N Bond in Carbamates of the 9-Azabicyclo[3.3.1]nonane System

Heterocycles ◽  
1985 ◽  
Vol 23 (4) ◽  
pp. 853 ◽  
Author(s):  
Takefumi Momose ◽  
Osamu Muraoka ◽  
Toshie Minematsu ◽  
Junko Tsuruzawa
Keyword(s):  
Dynamic Nmr ◽  
Nmr Studies ◽  
Restricted Rotation
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