Scalar couphng

Under fast MAS [P2(cosxm)=0] and neglecting the scalar coupHng term, the evolution phase of a symmetric coherence reduces to... 

The two frequency axes may consist of a diverse assortment of pairs of fundamental NMR parameters. Examples might include chemical shift on one axis and a frequency axis for scalar couplings on the second as in the 2D /-resolved NMR experiments. Both axes may be proton chemical shift, in which responses may be correlated by scalar (/) couphng as in the COSY experiment [46—48], by dipolar relaxation pathways as in the NOESY [35, 36, 49—51] and ROESY [35, 36, 52, 53] experiments, or by chemical exchange pathways as in the EXSY experiment [54—59]. Other examples may involve chemical shift on one axis and a multiple quantum frequency on the second axis. Examples here would include proton double [60 62] and zero quantum spectroscopy [63—67], C—INADEQUATE [68, 69], etc. The available axes in a 2D NMR experiment may also be used for hetero-nuclear chemical shift correlation, e.g. H—or H— N, where the respective nucHde pairs are correlated via their one-bond ( /xh) or multiple bond ("/xh) hetero-nuclear couphngs [14, 16, 17, 23—27, 29—31, 70—72]. 

B. Vogeb, J. Ying, A. Grishaev, A. Bax, Limits on variations in protein backbone dynamics from precise measurements of scalar coupHngs, J. Am. Chem. Soc. 129 (2007) 9377-9385. 

I. Alkorta, J. Elguero, Karplus-type relationships between scalar couphng constants Jhh molecular versus [Jhh supramolecular coupling constants, Theor. Chem. Acc. Ill (2004) 31. 

Spin system—a gronp of nnclear spins related by scalar conpling to each other traditionally restricted to those spins that show measurable H- H couphngs a single amino-acid residne is an example of a spin system. A dipeptide wonld contain two spin systems. 

Fig. 16. Extraction of dipolar couplings that add to the normal scalar couplings. By forming the difference between the observed splitting in anisotropic and isotropic medium, the couphng can be derived. It reflects orientation information of the...

P. Salvador, J.J. Dannenberg, Dependence upon basis sets of trans hydrogen-bond 13C-15N 3-bond and other scalar J-couphngs in amide dimers used as peptide models. A density functional theory study,. Phys. Chem. B 108 (2004) 15370. 

The fluorine-fluorine scalar coupling interactions have been found to be especially informative in structural investigations of a selection of various mono- and di-substituted octafluoro[2.2]paracyclophanes carried out by Roche and Marchione. In addition to Jpp and Jpp couphngs, these compounds also provided quite large, of about 2 Hz, couphngs across seven, and in some cases even eight bonds. 

The coupling terms Ay,- are made of two contributions, the nonadiabatic derivative couplings, Fji Q) = (Oy-(i, 2) V 0,-(r, Q)), which are vectors in the nuclear space, and the scalar nonadiabatic couphngs [second term on the right-hand side (RHS) of Eq. 8.7]. By differentiating Eq. 8.4 with respect to the normal coordinates Q, one easily obtains the following expression for the derivative couplings [17] ... 

The scalar spin-spin couphng term is omitted since the electron-coupled spin-spin interaction seems to be beyond the resolution achievable with techniques reported here. as defined in (3f) is the bulk magnetic susceptibility, and as defined in (3g) is the average magnetic shielding at the k-th nucleus. cannot be obtained spectroscopically since the term (2d) cancels out in subtracting energy levels of one and the same electronic state. 

---