Chemical shift correlations with molecular structure

Data on chemical shifts and discussions of empirical and semiempirical correlations with molecular structure are given in many books, including NMR Spectroscopy by Harald Giinther,64 NMR Spectroscopy by E A. Bovey,65 Interpretation of Carbon-13 NMR Spectra by EW.Wehrli andT.Wirthlin,66 15N NMR Spectroscopy by G. C. Levy and R. L. Lichter,67 and NMR of Newly Accessible Nuclei by Pierre Laszlo.68... 

In the case of an unknown chemical, or where resonance overlap occurs, it may be necessary to call upon the full arsenal of NMR methods. To confirm a heteronuclear coupling, the normal H NMR spectrum is compared with 1H 19F and/or XH 31 P NMR spectra. After this, and, in particular, where a strong background is present, the various 2-D NMR spectra are recorded. Homonuclear chemical shift correlation experiments such as COSY and TOCSY (or some of their variants) provide information on coupled protons, even networks of protons (1), while the inverse detected heteronuclear correlation experiments such as HMQC and HMQC/TOCSY provide similar information but only for protons coupling to heteronuclei, for example, the pairs 1H-31P and - C. Although interpretation of these data provides abundant information on the molecular structure, the results obtained with other analytical or spectrometric techniques must be taken into account as well. The various methods of MS and gas chromatography/Fourier transform infrared (GC/FTIR) spectroscopy supply complementary information to fully resolve or confirm the structure. Unambiguous identification of an unknown chemical requires consistent results from all spectrometric techniques employed. 

CORRELATING PROTON CHEMICAL SHIFTS WITH MOLECULAR STRUCTURE... 

With the aid of the H chemical shift correlation chart, Fig. 4.2, deduce the molecular structures of the molecules with the spectra shown in Figs. 4.15 and 4.16. 

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