China
Africa
Explore chapters and articles related to this topic
Nuclear Magnetic Resonance
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Other notable developments were occurring from the late 1950s onward that revolutionized the capability of NMR in structure elucidation. One such development involved the work of Martin Karplus [9] who established the relationship between vicinal three-bond scalar couplings and their dependence on bond angles. This empirical association of coupling constants with structural geometry enables solution conformational studies of complex organic molecules. Another major contribution was made by Albert Overhauser, whose pioneering work produced the nuclear Overhauser effect or NOE [10]. The NOE may be described as the transfer of nuclear spin polarization from one nuclear spin population to another via cross-relaxation. This work had a profound impact on structure elucidation as well as determination of stereochemistry and conformation for both small molecule and macromolecular systems.
Analysis of the interactions in FCCF:(H2O) and FCCF:(H2O)2 complexes through the study of their indirect spin–spin coupling constants
Published in Molecular Physics, 2018
María Cristina Caputo, Ibon Alkorta, Patricio F. Provasi, Stephan P. A. Sauer
The FC term is the dominant contribution, as in the 1J(C–C) case (see Table 3 of the supplementary material). The DSO and SD contributions are similar for all the complexes. However, this is not the case of the PSO term that varies between −1.3 and −15.5 Hz. The overall result is that the 1J(C-F) covers a 30 Hz range (between −289 and −256 Hz) while the FC term varies over 21 Hz. (between −247 and −268 Hz). In addition, the linear correlation coefficient, between the total 1J(F–C) values and the corresponding FC terms (R2 = 0.83), is smaller than in the 1J(C–C) case. The dependence of the 1J(F–C) coupling with the F–C bonding distance is displayed in Figure 6, where the solid circles correspond to the C2F2:nH2O complexes. The absolute value of the coupling constant is observed to decrease as the interatomic distance becomes larger. This behaviour, however, cannot be attributed to a mere dependence on the C2F2 geometry. The results for the 1J(F–C) couplings in isolated C2F2 molecules, where the molecular geometry is fixed to the one present in the complexes, indicate in fact that in this case the coupling slightly increases in absolute value with the C–F distance. This is illustrated by the open circles in Figure 7.