Heteronuclear spectra

The NMR spectra of heterocyclic compounds with seven or more ring members are as diverse as the shape, size and degree of unsaturation of the compounds. NMR is perhaps the most important physical method to ascertain the structure, especially the conformational statics and dynamics, of large heterocycles. Proton-proton coupling constants provide a wealth of data on the shape of the molecules, while chemical shift data, heteroatom-proton coupling constants and heteronuclear spectra give information of the electronic structure. Details are found in Chapters 5.16-5.22. Some data on seven-membered rings are included in Table 10. 

Treatment of 41b with bromocyanide (BrCN) at 70 °C for 3 h afforded the amino compound 53 (76%). The structures of all the newly synthesized compounds were confirmed by the H, NMR, and mass spectra. Compounds 55 and 52 were identified by the homo- and heteronuclear spectra, as well as from comparison to the 1,2,4-triazolo-azipene derivatives prepared previously [22] (Scheme 10). 

In principle, spin label effects can be observed in both homonuclear and heteronuclear spectra. When no isotope-enriched peptide is available, integration of TOCSY spectra in the presence and in the absence of spin label gives information of spatial proximity of... 

Fortunately, in proton spectroscopy it is generally possible to detect the presence of an aliased peak because of its esoteric phase which remains distorted when all others are correct. In heteronuclear spectra that display only a single resonance such phase characteristics caimot provide this information as there is no other signal with which to make the comparison. In such cases it is necessary to widen the spectral window and record any movement of the... 

The calibration of a NMR spectrum is based on the assignment of a reference signal to a known chemical shift. For heteronuclear spectra the standard frequency is based on the IH standard frequency SF and calculated according to equation [3-6]. The teaching version of NMR-SIM only support two rf channels and it is only necessary to set the parameters SF and 01 and 02. The radio frequency applied during the experiment is called SFOi where i refers to either the rf channel 1 or 2 and is defined in equation [3-... 

A pulse sequence suitable for acquiring ID heteronuclear spectra from DNP-NMR. 

Time reduction in homonuclear spectra using Hadamard spectroscopy Time reduction in heteronuclear spectra using Hadamard spectroscopy GFT NMR experiments for resonance assignments... 

---