Homonuclear internuclear distance

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. 

Table XXX. Dissociation Energies, Internuclear Distances and Vibration Frequencies of Homonuclear...

When more than two spins are present, the relationships for steady-state nOe become complicated by transfer of magnetization. However, the initial rate of buildup of nOe in multispin systems depends only on ajs, which for homonuclear relaxation is proportional to 7s- It is convenient to compare the initial ajs for a pair of protons of interest with those for a reference pair where the internuclear distance is known [433,440,441]. Then,... 

Fig.1a,b. Calculated line shape functions for special solid-state NMR signals of spin 7=1/2 nuclei. Spin pairs with dominating intra-pair homonuclear magnetic dipolar interaction, rn denotes the internuclear distance (a). Nearly isolated spins with dominating chemical shift anisotropy ()Jcsa=0-5) (b)... 

In an extension to experiments which measure internuclear distances, Levitt and co-workers and Griffin and co-workers have presented ingenious methods which allow the measurement of torsional angles [148, 149]. The methods involve the creation of MQC between a pair of nuclei (selective isotopic labelling is required), which may be homonuclear, e. g. or heteronudear, e. g. A spin-... 

Table 9.2. Homonuclear pairs of noble gas atoms well depths, Dm minimum-energy internuclear distances, i m, and van der Waals radii,...

The two-dimensional spin-echo experiment has found applications for static samples of compounds containing homonuclear spin pairs, where dipolar and chemical shift interactions could be separated allowing the determination of internuclear distances." " It was also shown that a considerable improvement in resolution could be obtained for samples rotated in the magic angle, thus allowing the determination of the magnitude of relatively smsdl homonuclear scalar coupling constants, e.g., P)ds in Wilkinson s-type rhodium complexes. ... 

---