Chemical shifts in the nuclear magnetic resonance spectra of molecules containing polar groups
01 Feb 1960-Canadian Journal of Chemistry (NRC Research Press Ottawa, Canada)-Vol. 38, Iss: 2, pp 300-307
TL;DR: In this paper, it was shown that the electric field at a particular nucleus arising from polar groups in other parts of a molecule can lead to chemical shifts proportional to the first power of the field strength.
Abstract: It is shown that the electric field at a particular nucleus arising from polar groups in other parts of a molecule can lead to chemical shifts proportional to the first power of the field strength....
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1,254 citations
TL;DR: In this paper, a consistent treatment of the chemical shift, thermal and dielectric data for water can be given based on a two-state model involving an equilibrium between a hydrogen-bonded ''icelike'' fraction and a ''monomer'' fraction whose interaction with the lattice arises entirely from London dispersion forces.
Abstract: Temperature‐dependence measurements have been made on the chemical shift of the proton of a water molecule in the liquid state and in the gas state at varying pressure. The problem of relating these experimental data to the intermolecular forces leading to cohesion and to hydrogen‐bond formation between water molecules is considered in detail. It is shown that a consistent treatment of the chemical shift, thermal, and dielectric data for water can be given based on a two‐state model involving an equilibrium between a hydrogen‐bonded ``icelike'' fraction and a ``monomer'' fraction whose interaction with the lattice arises entirely from London dispersion forces.Using semiempirically derived values of the chemical shift and energy associated with the condensation of water vapor to ``monomer,'' the magnitude of the shift associated with the transformation to ice is calculated. It is then shown that, on the assumption that the hydrogen bond is electrostatic in character, the ``polar'' contribution to this shif...
636 citations
TL;DR: It is suggested that if NMR-derived structures could be refined using heteronuclear chemical shifts calculated by SHIFTX, their precision could approach that of the highest resolution X-ray structures.
Abstract: A computer program (SHIFTX) is described which rapidly and accurately calculates the diamagnetic 1H, 13C and 15N chemical shifts of both backbone and sidechain atoms in proteins. The program uses a hybrid predictive approach that employs pre-calculated, empirically derived chemical shift hypersurfaces in combination with classical or semi-classical equations (for ring current, electric field, hydrogen bond and solvent effects) to calculate 1H, 13C and 15N chemical shifts from atomic coordinates. The chemical shift hypersurfaces capture dihedral angle, sidechain orientation, secondary structure and nearest neighbor effects that cannot easily be translated to analytical formulae or predicted via classical means. The chemical shift hypersurfaces were generated using a database of IUPAC-referenced protein chemical shifts – RefDB (Zhang et al., 2003), and a corresponding set of high resolution (<2.1 A) X-ray structures. Data mining techniques were used to extract the largest pairwise contributors (from a list of ∼20 derived geometric, sequential and structural parameters) to generate the necessary hypersurfaces. SHIFTX is rapid (< 1 CPU second for a complete shift calculation of 100 residues) and accurate. Overall, the program was able to attain a correlation coefficient (r) between observed and calculated shifts of 0.911 (1Hα), 0.980 (13Cα), 0.996 (13Cβ), 0.863 (13CO), 0.909 (15N), 0.741 (1HN), and 0.907 (sidechain 1H) with RMS errors of 0.23, 0.98, 1.10, 1.16, 2.43, 0.49, and 0.30 ppm, respectively on test data sets. We further show that the agreement between observed and SHIFTX calculated chemical shifts can be an extremely sensitive measure of the quality of protein structures. Our results suggest that if NMR-derived structures could be refined using heteronuclear chemical shifts calculated by SHIFTX, their precision could approach that of the highest resolution X-ray structures. SHIFTX is freely available as a web server at http://redpoll.pharmacy.ualberta.ca.
530 citations
04 Apr 2007
516 citations
TL;DR: In this paper, the chemical shifts of the 18-and 19-hydrogen atoms of 265 steroids of known structure have been recorded for 0-1M solutions in deuterochloroform and the positions of the signals of the 17-and 18-hydrogens atoms have been measured.
Abstract: The proton NMR spectra of 265 steroids of known structure have been recorded for 0,1M solutions in deuterochloroform and the positions of the signals of the 18-and 19-hydrogen atoms have been measured. The additional chemical shifts due to various substituents at many different positions of the steroid skeleton are compiled in a table. With its help most chemical shifts of the 18- and 19-hydrogen atoms of these and unknown steroids may be computed with an accuracy of ± 0,015 ppm. An example show how to calculate the chemical shifts. The physical basis of teh influences due to substituents and double bond, as well as the reasons for the generally small deviations from the calculated chemical shifts, are reviewed and illustrated. The additional chemical shifts due to identical funcitonal groups in equivalent positions, i. e. in approximately the same steric relation to one of the tertiary methyl groups, are collected in a table. Possible reason for teh variation of these additional chemical shifts within sets of identical functional functional groups in equivalent positions are discussed. The table furnishes interesting insights into the conformation of certain steroids and shows the average values and deviations one has to reckon with if the chemical shifts on methyl groups in non-steroidal compounds due to functional groups in corresponding positions to those in steroids are to be computed.
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TL;DR: In this article, a theoretical analysis of the fluorine magnetic resonance shifts in molecules is given, and it is shown that the large range of shifts among different fluorine compounds arises from the effects of binding on the magnetic fields at the nucleus produced by the orbital motion of the electrons in the unfilled valence shell.
Abstract: A theoretical analysis is given of the fluorine magnetic resonance shifts in molecules. It is shown that the large range of shifts among different fluorine compounds arises from the effects of binding on the magnetic fields at the nucleus produced by the orbital motion of the electrons in the unfilled valence shell. The simple dependence on ionic character of the bond is also explained. The chemical shift between F2 and HF is calculated to be 14×10—4 compared to the experimentally observed value 6.3×10—4.
362 citations
TL;DR: In this article, the authors studied the factors giving rise to proton resonance chemical shifts of free molecules, as well as the association shifts due to hydrogen bonding, and found that the proton signals measured in the liquid state near the melting point, which correspond to maximum association, show large shifts to lower magnetic field relative to the corresponding gas signals.
Abstract: In order to study the factors giving rise to proton resonance chemical shifts of free molecules, as well as the association shifts due to hydrogen bonding, proton resonance measurements were carried out for a variety of simple hydride molecules in both the liquid and gaseous states. It is found that the proton shifts in the gaseous state can be interpreted in terms of the combined effect of the electronegativity and magnetic anisotropy of the atom to which the proton is bonded. The proton signals measured in the liquid state near the melting point, which correspond to maximum association, show large shifts to lower magnetic field relative to the corresponding gas signals. It is suggested that the association, or hydrogen bond shifts, in a system Y ——— H — X can be interpreted largely in terms of the reduction of the diamagnetic circulation in the H — X bond by the electrostatic field of the Y donor. Further possible contributions in certain anomalous cases are also considered.
278 citations
TL;DR: In this article, the authors proposed an experiment whose object is the determination of permanent molecular quadrupole moments, which is analogous to those used in measurements of electrooptical Kerr constants, but the uniform electric field proportional to the applied voltage V is replaced by the field gradient of a square fourwire condenser.
Abstract: An experiment whose object is the determination of permanent molecular quadrupole moments is suggested. It is analogous to those used in measurements of electro‐optical Kerr constants, but the uniform electric field proportional to the applied voltage V is replaced by the field gradient of a square four‐wire condenser. If the wires at x=±a are at a potential V relative to those at y=±a, then the field gradient on the z axis will tend to orient quadrupolar molecules so that a fluid in the condenser will become doubly refracting. The induced anisotropy in the refractive index of a gas is shown to be first order in the applied voltage and of the form nx—ny=[B+(A/T)]V, while in the Kerr effect it is second order in V, and is given by nx—ny=[C+(D/T)+(E/T 2)]V2. The constant A is proportional to the molecular quadrupole moment and to the anisotropy in the polarizability, while B is proportional to the quadrupole moment induced in a molecule by a uniform field. In spherical molecules A, D, and E are zero. Calcul...
213 citations
TL;DR: In this paper, the nuclear magnetic screening constant of a hydrogen atom in a uniform electric field is calculated, neglecting any effect of electron spin, and the screening is found to be reduced by the electric field for all directions of the applied magnetic field, the reduction being greatest if the two fields are perpendicular.
Abstract: The nuclear magnetic screening constant of a hydrogen atom in a uniform electric field is calculated, neglecting any effect of electron spin. The screening is found to be reduced by the electric field for all directions of the applied magnetic field, the reduction being greatest if the two fields are perpendicular.
114 citations