Selective heteronuclear

The selective heteronuclear /-resolved experiment (Bax, 1984) is used to determine heteronuclear long-range coupling constants via a selecdve n pulse that causes splitting of all carbon signals coupled to that proton. 

Acquisition scheme for the multiple selective heteronuclear inverse detected ID COSY experiment. Four experiments have to be performed with 3 carbon resonances selected for selective perturbation. The frequencies are set either on-resonance (/i, fi, /j) or off-resonance to the selected resonance frequencies. 

Processing scheme for the multiple selective heteronuclear inverse detected ID COSY experiment. The final spectra A, B, C corresponding to the selective perturbation of three carbons resonating at frequencies fi, fi, and f are obtained by linear combination of the original data a, b, c and d acquired in accordance with the acquisition scheme (table 1). 

S. N. Suchard, "Spectroscopic Constants for Selected Heteronuclear Diatomic Molecules, Aerospace report No. TR-0074 (4641)-6, 1974. 

Another ID experiment that can be and has been utilized for 29Si line assignment in even more difficult situations [with /(29Si—13C) 1-2 Hz] is selective heteronuclear INADEQUATE253,254. ID heteronuclear INADEQUATE with 13C detection is a simple two-step pulse sequence in which the pulses are applied simultaneously to both nuclei ... 

FIGURE 39. The 29Si satellites in the 13C NMR spectra of 2 at 90.6 MHz measured with the selective heteronuclear INADEQUATE (the 29Si line selectively irradiated is indicated on the left for each trace, 13C assignment is given on the top). Total experimental time 15 min. Reproduced by permission of John Wiley Sons, Ltd from Reference 253... 

Spectroscopic Constants for Selected Heteronuclear Diatomic Molecules (Air Force Report No. SAMSO-TR-74-82), Vol. II, p. N102. 1982. 

B. Band-Selective Heteronuclear Hartmann-Hahn Experiments... 

Broadband Hartmann-Hahn sequences, such as DIPSI-2 or WALTZ-16, can be made band-selective by reducing the rf amplitude of the sequences (Brown and Sanctuary, 1991). Richardson et al. (1993) used a low-amplitude WALTZ-17 sequence for band-selective heteronuclear Hartmann-Hahn transfer between N and in order to minimize simultaneous homonuclear Hartmann-Hahn transfer between and The DIPSI-2 sequence was successfully used by Gardner and Coleman (1994) for band-selective Hartmann-Hahn transfer between C d and H spins. So far, no crafted multiple-pulse sequences have been reported that were optimized specifically for band-selective heteronuclear Hartmann-Hahn transfer. Based on the results of Section X, it is expected that such sequences with well defined regions for coherence transfer and effective homonuclear decoupling will result in increased sensitivity of band-selective heteronuclear Hartmann-Hahn experiments. 

Covalent radii estimated from homonuclear bond lengths where available and from selected heteronuclear bonds otherwise. Bond lengths from Tables of Interactomic Distances and Configuration in Molecules and Jons) Sutton. L., Ed. Spec. Publ. Nos. 11 and 18 The Chemical Society London, 1958, 1%5, except where noted. Values in parentheses are for noble gases not known to form compounds and are extrapolated from the values of neighboring nonmetals Allen, L. C. Huheey, J. E. J. Jnorg. NucJ. Chem. 1980, 42, 1523. 

By analogy with homonuclear decoupling above, selective heteronuclear decoupling is also possible. The decoupling of a single proton resonance could in... 

Figure 7.6. The proton-detected selective heteronuclear J-resolved spectrum of adenosine 73. The HI proton has been selectively inverted and the doublet splittings in f record its long-range couplings to C8 and C2 (reproduced with permission from reference [6]).

When we collect a 2-D NMR spectrum, both the second frequency dimension data (fj or Fj) and the first frequency dimension data (f2 or F2) may be phase sensitive. (Note that fj and f2 appear to be reversed but this naming convention derives from the order of their time domain precedents, tj and t2, in the NMR pulse sequence.) Zero-and first-order phasing of the second dimension of a 2-D NMR data set is required in many cases. Some experiments, most notably the gradient-selected heteronuclear multiple bond correlation (gHMBC) experiment, use the absolute value of the signal and hence do not require phasing. 

It is also possible through selective heteronuclear singlefrequency decoupling to correlate bonded carbons and protons (HETCOR, Heteronuclear Correlated Spectroscopy) as an alternative to identify all directly bonded and longdistance carbon-proton pairs in a molecule. 

Figure 7.5. A region of the selective heteronuclear /-resolved spectrum of 7.2. Long-range heteronuclear couplings to the selected proton appear as splittings in/i, the values of which are shown. The vertical trace is taken through the resonance at 199 ppm. 4K 2 data points were collected for 32 fi-increments over spectral widths of 100 ppm and MHz, respectively. A 100ms Gaussian 180° pulse was used to select the proton resonance. The final /i resolution after zero-filling was 0.1 Hz/pt.

Berger (1989) anticipated the solution to the problem of needing experimental access to selective heteronuclear shift connectivities with the development of a selective ID analog of the HMQC experiment to which he gave the acronym SELINCOR. Simply, SELINCOR replaces the final 90° carbon pulse of the HMQC experiment (see Fig. 1) with a selective Gaussian 90° pulse applied to the C resonance of interest. SELINCOR has had no practical applications but was certainly of interest in a developmental sense. 

---