Chemical Shift. V. Further Studies on the Long-range Shielding Effects of the C—H and C=O Bonds

1971 ◽  
Vol 49 (9) ◽  
pp. 1328-1334 ◽  
Author(s):  
J. W. ApSimon ◽  
H. Beierberck
Keyword(s):  
Chemical Shift ◽  
Magnetic Anisotropy ◽  
Long Range ◽  
Methyl Groups ◽  
X Ray ◽  
X Ray Crystallography ◽  
Geometric Factors ◽  
Atomic Coordinates ◽  
Shielding Effects

The long-range shielding effects of the C=O and C—H bonds were reexamined by the method described in part IV of this series, with the objective of resolving the discrepancies between some of the conclusions presented and earlier findings by Zürcher. The C—H bond magnetic anisotropy was treated as a variable and found to be small enough to be negligible. Upon omission of this term, both electrostatic and magnetic anisotropy effects had to be invoked to account for the shielding effects of the carbonyl group.The necessary geometric quantities were calculated from atomic coordinates for androsterone, as determined by X-ray crystallography, and freely rotating methyl groups were approximated by superpositions of 24 conformations of the group. The results were in essential agreement with those obtained with the use of geometric factors computed as described in part IV.

Computational, 1H NMR, and X-ray structural studies on 1-arylurazole tetrazane dimers

2017 ◽  
Vol 73 (9) ◽  
pp. 660-666 ◽  
Author(s):  
Kenneth L. Martin ◽  
Gary W. Breton
Keyword(s):  
Methyl Groups ◽  
Structural Studies ◽  
Aromatic Rings ◽  
Nmr Spectrum ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Dimeric Form ◽  
Shielding Effects

Nitrogen-centered urazole radicals exist in equilibrium with tetrazane dimers in solution. The equilibrium established typically favors the free-radical form. However, 1-arylurazole radicals bearing substituents at the ortho position favor the dimeric form. We were able to determine the structure of one of the dimers (substituted at both ortho positions with methyl groups), namely 1,2-(2,4-dimethylphenyl)-2-[2-(2,4-dimethylphenyl)-4-methyl-3,5-dioxo-1,2,4-triazolidin-1-yl]-4-methyl-1,2,4-triazolidine-3,5-dione, C24H28N6O4, via X-ray crystallography. The experimentally determined structure agreed well with the computationally obtained geometry at the B3LYP/6-311G(d,p) level of theory. The preferred syn conformation of these 1-arylurazole dimers results in the two aromatic rings being proximate and nearly parallel, which leads to some interesting shielding effects of certain signals in the 1H NMR spectrum. Armed with this information, we were able to decipher the more complicated 1H NMR spectrum obtained from a dimer that was monosubstituted at the ortho position with a methyl group.

Probing solid iminobis(diorganophosphine chalcogenide) systems with multinuclear magnetic resonance

2009 ◽  
Vol 87 (1) ◽  
pp. 348-360 ◽  
Author(s):  
Bryan A Demko ◽  
Roderick E Wasylishen
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Solid State Nmr ◽  
Magnetic Shielding ◽  
Chemical Shift Tensors ◽  
X Ray ◽  
X Ray Crystallography ◽  
Shielding Tensor ◽  
Nuclear Magnetic Shielding Tensors ◽  
Nuclear Magnetic

A 31P and 77Se solid-state NMR investigation of the iminobis(diorganophosphine chalcogenide) HN(R2PE)2 (R = Ph,iPr; E = O, S, Se) systems is presented. The NMR results are discussed in terms of the known HN(R2PE)2 structures available from X-ray crystallography. The phosphorus chemical shift tensors are found to be sensitive to the nature of the alkyl and chalcogen substituents. The nature of the R group also influences the selenium chemical shift tensors of HN(R2PSe)2 (R = Ph, iPr), which are shown to be sensitive to hydrogen bonding in the dimer structure of HN(Ph2PSe)2 and to the presence of disorder in the case of HN(iPr2PSe)2. Scalar relativistic ZORA DFT nuclear magnetic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors. A theoretical investigation into the effect of the E-P···P-E “torsion” angle on the phosphorus and selenium chemical shift tensors of a truncated HN(Me2PSe)2 system indicates that the electronic effect of the alkyl group on the respective nuclear magnetic shielding tensors are more important than the steric effect of the E-P···P-E torsion angle.Key words: iminobis(diorganophosphine chalcogenide), solid-state NMR, 31P NMR, 77Se NMR, ZORA DFT.

Chemical Shift. VII. The Long-range Shielding Effects of the Cyano Group

1972 ◽  
Vol 50 (14) ◽  
pp. 2351-2356 ◽  
Author(s):  
J. W. ApSimon ◽  
H. Beierbeck ◽  
D. K. Todd
Keyword(s):  
Chemical Shift ◽  
Long Range ◽  
Field Effect ◽  
Cyano Group ◽  
Electric Field Effect ◽  
Minor Contribution ◽  
Anisotropy Effect ◽  
A Minor ◽  
Good Agreement ◽  
Shielding Effects

Using the methods described in parts I–VI of this series, we have examined the long-range shielding effects of the cyano group upon the C-18 and -19 methyl protons in several cyano-steroids and the ring protons in 2-endo- and 2-exo-cyanonorbornenes.It was found that the most important shielding mechanism of the cyano group is its electric field effect, with the magnetic anisotropy effect making at most a minor contribution to the screening. However, only in the cases of the cyano-steroids was good agreement obtained between the calculated and the experimental shifts.

SUBSTITUTIONAL AND CONFIGURATIONAL EFFECTS ON CHEMICAL SHIFT IN PYRANOID CARBOHYDRATE DERIVATIVES

1965 ◽  
Vol 43 (7) ◽  
pp. 2059-2070 ◽  
Author(s):  
R. U. Lemieux ◽  
J. D. Stevens
Keyword(s):  
Chemical Shift ◽  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Equatorial Orientation ◽  
Free Energies ◽  
Bonding Interaction ◽  
Conformational Properties ◽  
Good Agreement ◽  
Shielding Effects

The effects of long-range and virtual long-range coupling on the observed spectra of acetylated hexopyranoses and pentopyranoses are examined. Use is made of both spin decoupling and specific deuteration for the assignment of signals. It is seen that specific solvent effects on chemical shift can be superior to increasing the applied magnetic field for the resolution of the signals of closely related protons. The alteration of virtual long-range coupling effects in these ways can be useful in the diagnosis of spectra. Empirical rules are derived for estimating the long-range shielding effects which occur on changing configurations. It is seen that the inversion of a center can lead to deshielding of axial protons and to shielding of equatorial protons at other centers relative to the chemical shifts observed in reference compounds wherein all the acetoxy groups are in equatorial orientation. The effects in several cases result in equatorial protons giving their signal to higher field than chemically similar but axial protons. The conformational properties of pentopyranose tetraacetates as estimated from chemical shifts and coupling constants are seen to be in good agreement with expectations based on non-bonding interaction free energies. As expected, 2-deoxy-β-D-ribopyranose triacetate has the 1C-conformation when dissolved in chloroform.

Chemical Shift. VI. The Long-range Shielding Effects of Ethylene–Ketal and −Thioketal Groups

1971 ◽  
Vol 49 (9) ◽  
pp. 1335-1338 ◽  
Author(s):  
J. W. ApSimon ◽  
H. Beierbeck ◽  
D. K. Todd ◽  
P. V. Demarco ◽  
W. G. Craig
Keyword(s):  
Chemical Shift ◽  
Electric Field ◽  
Long Range ◽  
Field Effect ◽  
Chemical Shifts ◽  
Electric Field Effect ◽  
Electric Dipoles ◽  
Derivatives Of ◽  
Shielding Effects

The calculation of chemical shift values by the method used in parts I–V (1–5) has been extended to a derivation of the shielding effects of the ethylene–ketal and −thioketal groups. For these studies ketal and thioketal derivatives of monoketoandrostanes were prepared. The chemical shifts of the C-18 and -19 methyl protons in these compounds are reported for the solvents CDCl3, CCl4 and benzene.Representing both groups by point dipoles, values for the anisotropies and for K, a parameter descriptive of the electric field effect, were derived for various, coincidental, locations of the magnetic and electric dipoles along the symmetry axes of the two groups.

scholarly journals IP3-mediated gating mechanism of the IP3 receptor revealed by mutagenesis and X-ray crystallography

2017 ◽  
Vol 114 (18) ◽  
pp. 4661-4666 ◽  
Author(s):  
Kozo Hamada ◽  
Hideyuki Miyatake ◽  
Akiko Terauchi ◽  
Katsuhiko Mikoshiba
Keyword(s):  
Long Range ◽  
Conformational Dynamics ◽  
Ip3 Receptor ◽  
X Ray ◽  
Allosteric Coupling ◽  
X Ray Crystallography ◽  
Helical Domain ◽  
Gating Mechanism ◽  
Cytosolic Domain

The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) is an IP3-gated ion channel that releases calcium ions (Ca2+) from the endoplasmic reticulum. The IP3-binding sites in the large cytosolic domain are distant from the Ca2+ conducting pore, and the allosteric mechanism of how IP3 opens the Ca2+ channel remains elusive. Here, we identify a long-range gating mechanism uncovered by channel mutagenesis and X-ray crystallography of the large cytosolic domain of mouse type 1 IP3R in the absence and presence of IP3. Analyses of two distinct space group crystals uncovered an IP3-dependent global translocation of the curvature α-helical domain interfacing with the cytosolic and channel domains. Mutagenesis of the IP3R channel revealed an essential role of a leaflet structure in the α-helical domain. These results suggest that the curvature α-helical domain relays IP3-controlled global conformational dynamics to the channel through the leaflet, conferring long-range allosteric coupling from IP3 binding to the Ca2+ channel.

Six pyrimidonium salts: determination of their crystal structures and studies of their prototropic behaviour in solution

1984 ◽  
Vol 62 (6) ◽  
pp. 1194-1202 ◽  
Author(s):  
Thomas W. S. Lee ◽  
Steven J. Rettig ◽  
Ross Stewart ◽  
James Trotter
Keyword(s):  
Hydrogen Exchange ◽  
Molecular Geometry ◽  
High Reactivity ◽  
Methyl Groups ◽  
Contributing Factors ◽  
X Ray ◽  
X Ray Crystallography ◽  
Reactive Compound ◽  
Chloride Salts

Six methyl-substituted 2-pyrimidonium chloride salts have been prepared and the rates of hydrogen exchange of their reactive methyl groups (at the 4- and 6-positions) have been determined in DCl/D2O solution. Adjacent methyl groups, whether on nitrogen or carbon, activate the exchanging centres, whereas more distant methyl groups have a deactivating effect. The molecular geometry of the salts has been determined by X-ray crystallography with the view to determining whether the presence of strain in the pyrimidonium ring can account for the activating effect of adjacent methyl. The most reactive compound, the 1,5,6-trimethylpyrimidonium chloride, has a geometry that is consistent with high reactivity, viz. a non-planar ring and short H … H intermethyl distance. However, the 1,4,5,6-tetramethyl compound, which also is non-planar and has an extremely short 5-6 intermethyl distance (1.99 Å), is not highly reactive; that is, the heightened strain is unable to overcome the deactivating inductive effect of the additional methyl group. We conclude that deviations from ring planarity and short intermethyl distances are insufficient to account for the activation produced by adjacent methyl though they appear to be contributing factors to this effect.

scholarly journals Insights into the formation of chiral second sphere coordination complexes with aromatic tris amines: combined single crystal X-ray crystallography and molecular modeling analyses

2015 ◽  
Vol 44 (36) ◽  
pp. 15960-15965 ◽  
Author(s):  
Hong-Cui Yu ◽  
Lei Li ◽  
Ji Gao ◽  
Jian Tong ◽  
Wenxu Zheng ◽  
...  
Keyword(s):  
Molecular Modeling ◽  
Single Crystal ◽  
Aromatic Ring ◽  
Coordination Complexes ◽  
Methyl Groups ◽  
X Ray ◽  
X Ray Crystallography

Bulky methyl groups on the central aromatic ring in chiral isostructural second sphere coordination adducts are crucial for the induction of chirality.

SYNTHESIS OF NOVEL MANGANESE-BASED SINGLE-MOLECULE NANOMAGNETS

2002 ◽  
Vol 01 (05n06) ◽  
pp. 455-459 ◽  
Author(s):  
JINKWON KIM ◽  
HAENGKYU CHO ◽  
AHKILESH K. GUPTA ◽  
JIN MOOK LIM ◽  
YOUNGKYU DO
Keyword(s):  
Magnetic Susceptibility ◽  
Magnetic Anisotropy ◽  
Single Crystal ◽  
Single Molecule ◽  
Ac Susceptibility ◽  
Ac Magnetic Susceptibility ◽  
Temperature Dependent ◽  
X Ray ◽  
X Ray Crystallography

New Mn12 single-molecule nanomagnets [ Mn 12 O 12( O 2 CCHCl 2)( H 2 O )4]· 2CH 2 Cl 2· H 2 O and [ Mn 12 O 12( O 2 CCHCl 2)( H 2 O )4]· 2CH 3 C 6 H 5· 4H 2 O and novel Mn18 complexes [ M 18 O 14( O 2 CR )18( hmp )4( hmpH )2( H 2 O )2] (R=Me, Et) have been synthesized and characterized by single crystal X-ray crystallography and dc- and ac-magnetic susceptibility measurements. Mn12 complexes show characteristic SMM properties, such as temperature-dependent out-of-phase ac-susceptibility. Mn18 does not show relaxation behaviors down to 2.0 K, but reveals magnetic anisotropy in reduced magnetization experiment.

NMR, IR, Mössbauer and quantum chemical investigations of metalloporphyrins and metalloproteins

2001 ◽  
Vol 05 (03) ◽  
pp. 323-333 ◽  
Author(s):  
LORI K. SANDERS ◽  
WILLIAM D. ARNOLD ◽  
ERIC OLDFIELD
Keyword(s):  
Chemical Shift ◽  
Electric Fields ◽  
Heme Proteins ◽  
Density Functional ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Chemical Shift Tensors ◽  
X Ray ◽  
X Ray Crystallography ◽  
Isotropic Chemical Shifts

We review contributions made towards the elucidation of CO and O 2 binding geometries in respiratory proteins. Nuclear magnetic resonance, infrared spectroscopy, Mössbauer spectroscopy, X-ray crystallography and quantum chemistry have all been used to investigate the Fe –ligand interactions. Early experimental results showed linear correlations between 17 O chemical shifts and the infrared stretching frequency (νCO) of the CO ligand in carbonmonoxyheme proteins and between the 17 O chemical shift and the 13CO shift. These correlations led to early theoretical investigations of the vibrational frequency of carbon monoxide and of the 13 C and 17 O NMR chemical shifts in the presence of uniform and non-uniform electric fields. Early success in modeling these spectroscopic observables then led to the use of computational methods, in conjunction with experiment, to evaluate ligand-binding geometries in heme proteins. Density functional theory results are described which predict 57 Fe chemical shifts and Mössbauer electric field gradient tensors, 17 O NMR isotropic chemical shifts, chemical shift tensors and nuclear quadrupole coupling constants (e2qQ/h) as well as 13 C isotropic chemical shifts and chemical shift tensors in organometallic clusters, heme model metalloporphyrins and in metalloproteins. A principal result is that CO in most heme proteins has an essentially linear and untilted geometry (τ = 4 °, β = 7 °) which is in extremely good agreement with a recently published X-ray synchrotron structure. CO / O 2 discrimination is thus attributable to polar interactions with the distal histidine residue, rather than major Fe–C–O geometric distortions.

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