Heteronuclear double resonance

EXAMPLE 12.1 Suppose we were to observe the H spectrum of CH2F2 (Section 8.6.1) at a field strength of 5.87 T, while simultaneously irradiating the fluorines, (a) Does this experiment involve homo- or heteronuclear double resonance (b) What are the values of v, v2, and the difference (Av) between them ... 

Homonuclear double resonance indicates that both V and v2 are focused on nuclei of the same isotope, while heteronuclear double resonance indicates that the V and v2 are focused on different isotopes or elements. 

In the previous article (1) on heteronuclear double resonance in this series it was suggested that such experiments would soon vie for importance with homonuclear ones. In fact, there has been an almost total eclipse partly as a result of the use of proton decoupling in all work, partly because of improved methods of frequency generation and control which have made experimental distinctions between the two types of experiment much less important. The present review therefore deals with both homo- and hetero-nuclear experiments and includes multiple resonance work also. The seven years up to mid-1978 are covered, although it has been impossible to mention every experiment. Emphasis is laid upon new ideas and developments of technique, with some preference for the more recent work. The Chemical Society specialist reports on NMR spectroscopy have included regular articles on multiple resonance (2,3) and a number of reviews deal with various aspects of the subject. (4-19) It has been decided to omit work on the solid state. 

When the two sets of nuclei are of different isotopes (e.g., C and H), the experiment is described as heteronuclear double resonance. When we observe the signal from nuclei of isotope A while irradiating nuclei of isotope B, we label the resulting spectrum with the shorthand designation A (B). When the two sets of nuclei belong to the same isotope (e.g., both H), the technique is described as homonuclear double resonance. 

Numerous ID heteronuclear double resonance experiments of various types (e.g. H Sn, etc.) have been carried out already in the 1960s and... 

Experiments in which both the irradiated and the observed nuclei are protons are called homonuclear double-resonance experiments and are represented by the notation The irradiated nucleus is denoted by braces. When the observed and irradiated nuclei are different nuclides, as in proton-decoupled spectra, the experiment is a heteronuclear double-resonance experiment and is denoted, for example, C H. ... 

UB n.m.r. data, including heteronuclear double-resonance, UB—PH, have been reported for ortho-, meta-, and para -isomers of the 12-carbaboranes and their B-monohalogeno-derivatives.95... 

Alkyne complexes of platinum have also been prepared from 3,3,3-trifluoropropyne, and parameters for compounds [293] to [295] are given in Table XVII. (151) Parameters for the silylacetylene complex rra/ii-Pt(PEt3)2(Cl)(SiH2C]CCF3), 5—51-3 for the terminal CF3 group, with 5/(Pt-F) +23-7 Hz and 5/(F-H) 2-2 Hz, were obtained by heteronuclear double resonance. (162)... 

Heteronuclear Double Resonance Experiments. - 5.5.i HSQC HMQC. A number of modifications were proposed for detection of long-range... 

In triethylphosphine complexes of the type cis- and trans-[PtCl2(Et3P)2], heteronuclear double-resonance experiments have shown that the signs of the Jpcn - pcch coupling constants are negative and positive, respectively. ... 

P-23 - Characterization of acidic sites in zeolites by heteronuclear double resonance solid state NMR... 

Only one example is known for /( Si, Be) = 51 Hz in (/ -C5H5)Be-SiMe3 (65) For tri-coordinate silylboranes, the Si NMR signals are broad owing to partially relaxed Si-"B spin-spin coupling. In one case (66), the magnitude and sign of /( Si,"B) has been determined by H Si heteronuclear double-resonance experiments. Resolved 1 1 1 1 quartets (67) as the result of j( Si,"B) are observed for silylborates (Scheme 16). 

Indirect detection of nuclei by heteronuclear double resonance (INDOR) Baker, J. Chem. Phys. 37 911... 

The use of heteronuclear double resonance is exemplified by a study of alumichrome, an analogue of ferrichrome in which iron has been replaced by aluminum (Llinas et al, 1977a). The proton spectrum, including N-H... 

In the heteronuclear double-resonance dipolar decoupling process, residual line broadening will occur when the proton rf field is off resonance or when the decoupling field is low. For solids, the proton irradiation is always off resonance because the protons have anisotropic chemical-shift tensors. It has been suggested [22] that the off-resonance effect (assumed to be 4 ppm) can contribute a broadening of 1.0-2.4 Hz at a field of 1.4 T. 

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