摘要:

AbstractLocalizedin vivospectroscopic studies are generally performed with successive, spatially orthogonal, slice‐selective radio‐frequency (rf) pulses so that the received signal is confined to a particular volume of interest. Although these techniques spatially restrict the signal, successive rf pulses applied prior to signal acquisition give rise to complex spectral modulations for coupled spin systems. Interpulse timing delays, rf flip angles, and phases all affect these modulations, which must be fully understood and appreciated if sequences are to be optimized for specificin vivospectroscopic studies. The density matrix formalism is particularly suited for this task. Our purpose is to demonstrate how the density matrix formalism is used to study spectral modulations induced by selected multipulse sequences for an AB sys

ISSN:1043-7347    

DOI:10.1002/cmr.1820060102

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractA vector model correctly predicts the correlated motion of weakly coupled spins. The model is semiclassical when the spins are interacting and fully classical when all spins are transverse and not interacting. A simple two‐pulse experiment and the Heteronuclear Multiple Quantum Coherence (HMQC) experiment are analyzed. The model is extended to the relativistic limit and discussed in the context of the Einstein, Rosen, Podolsky gedanken experiment and the twin parado

ISSN:1043-7347    

DOI:10.1002/cmr.1820060103

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractVicinal proton‐proton coupling constants depend on a variety of stereochemical parameters such as bond angle, bond length, substituent electronegativity and orientation, and — most importantly — on the torsion angle between the coupling protons. The sensitivity of vicinal proton‐proton coupling constants3JHH′, to variations of dihedral angle ϕwas first rationalized in valence bond terms by Karplus, who showed that the coupling constants could be approximately fitted to a cos2ϕ function. The Karplus equation3JHH′= Acos2ϕ + Bcosϕ + C (or variants thereof) has been a major tool of the structural chemist for 35 years. Karplus started with the Ramsey formula for Fermi contact contribution, expressed by ground‐state wave functions and a mean excitation energy. More sophisticated molecular orbital (MO) treatments have afforded analogous expressions that may be used to predict trends correctly but are rarely useful for accurate estimations of dihedral angles. Numerous attempts have been made to account for the effect of substituents, bond angles, and lengths — either empirically by the choice ofA,B, andC(with different values for each type of compound) or semiempirically, starting with theoretically more sophisticated expressions with statistically adjustable parameters. Theoretical and empirical approaches are re

ISSN:1043-7347    

DOI:10.1002/cmr.1820060104

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractA simplified explanation of the modified Gauss‐Newton linearization (curve‐fitting) procedure is presented by translating this algorithm into a spreadsheet with examples from various single‐ and multiple‐pulse NMR experiments. Comparisons are made with linear regression analysis of mathematically manipulat

ISSN:1043-7347    

DOI:10.1002/cmr.1820060105

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820060106

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820060107

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820060108

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820060101

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY