Scalar couplings involving

We have previously considered ID and 2D spectra involving the coupling of nuclei through bonds scalar coupling, or f-coupling). Nuclei can... 

Various theoretical formalisms have been used to describe chemical exchange lineshapes. The earliest descriptions involved an extension of the Bloch equations to include the effects of exchange [1, 2, 12]. The Bloch equations formalism can be modified to include multi-site cases, and the effects of first-order scalar coupling [3, 13, 24]. As chemical exchange is merely a special case of general relaxation theories, it may be compre-... 

Significant through-space scalar couplings have been observed only in rare cases and in very close spatial proximity and usually 19F is involved in such couplings102-105, e.g., in the following fluorinated polycyclic aromatic systems ... 

It should be remarked that this is the first practical implementation of the calculation of spin-spin couplings involving heavy atoms applicable to medium sized molecular systems. Formerly, Khandogin and Ziegler101 developed a frozen core scalar relativistic approach in combination with the non-relativistic FC and PSO operators, but the quality of results thus obtained is poorer than those obtained with ZORA. 

There is a simple and well-known model for the description of DNMR phenomenon, provided no scalar coupling is involved.11 In Section 3.2.1, the macroscopic magnetisation vector of the vector model gives the detected signal (the FID). This vector rotates in the xy plane perpendicular to the direction of the external magnetic field during the detection its frequency is determined by the shielding effect of the chemical environment of the nuclei. 

Multidimensional NMR spectra are not restricted to cases where the separate frequency axes encode signals from different nuclear types. Indeed, much of the early work on the development of 2D NMR was performed on cases where both axes involved chemipal shifts. The main value in such spectra comes from the information content in cross peaks between pairs of protons. In COSY-type spectra (COSY = Correlation SpectroscopY) cross peaks occur only between protons that are scalar coupled (i.e., within 2 or 3 bonds) to each other, whereas in NOESY (NOE Spectroscopy) spectra cross peaks occur for protons that are physically close in space (<5 A apart). A combination of these two types of 2D spectra may be used to assign the NMR signals of small proteins and provides sufficient information on internuclear distances to calculate three-dimensional structures. Figure 12.3 includes a panel showing the COSY spectrum of cyclosporin and highlights the relationships between ID H-NMR spectra and corresponding 2D homonuclear (COSY) and heteronuclear (HSQC) spectra. 

As for liquids, scalar coupling constants can be directly observed in solids only if the nuclei involved in the coupling have sufficiently long relaxation times, i.e. 

Trebosc et al. introduced a frequency-selective (FS) REDOR approach to a multi-spin system Sl y where S is a quadrupolar nucleus. FS-REDOR may be used for accurate trough-space distance measurements in spin pairs that involve quadrupolar nuclei [106]. The experiment reveals heteronuclear dipolar and scalar couplings, which can be reintroduced selectively, site after site. Importantly, FS-REDOR may also be used under high-resolution provided by MQMAS, STMAS or I-STMAS. 

In addition to using /-scalar coupling data (see above), several other methods have been proposed to estimating sugar conformations in RNA based on the 13C-4H dipole-dipole cross-correlated relaxation,289 based on the cross-correlated relaxation rates involving 13C CSA and 13C-4H dipolar interactions,290 and based on the 13C chemical shifts of sugar carbons.291... 

---