Noise-decoupled C-13 NMR

Infrared spectra were recorded with a Perkin-Elmer 685-IR spectrophotometer. Thin film of polymer in CHCl or THF was cast on NaCl pellet which was used for this purpose. IH-NMR were recorded using Varian FX-lOO (100 MHz) FT NMR or Bruker AM 500 MHz FTNMR spectrometer using TMS as internal standard. Noise decoupled C-13 NMR... 

Figure 5. Proton noise-decoupled 22.6-MHz C-13 NMR spectrum of the hydrogenated 1,4-polyisoprene sample. Perdeuteriohenzene solution at 25°C with TMS as internal reference. Approximately 5000 pulses with an acquisition time of 0.7 sec and a flip angle of 30°.

The noise-decoupled and off-resonance C-13 NMR spectra of chloroquine are presented in Figures 7 and 8 respectively. The spectra were obtained on Varian FT-80A Spectrometer Spectral assignments are listed in Table 3. 

Carbon - 13. Use of C in NMR developed slowly because of the low natural abundance of this isotope. Another complication was the occurrence of coupling involving the many protons normally present in organic compounds. The latter problem was solved by the development of wide-hand proton decoupling (noise decoupling). With a natural abundance of only 1.1%, C is rarely present in a molecule at adjacent positions. Thus, C- C coupling does not introduce complexities and in a noise-decoupled natural abundance spectrum each carbon atom gives... 

Austin (89) is clearly biosynthetically related to andibenin B and is formed from the same key intermediate (86). An interesting possibility was that the tetracyclic intermediate (91) involved in austin biosynthesis (Scheme 24) is not formed directly from cyclisation of (86) but is formed via the same bicyclo-farnesyl intermediate (87) involved in andibenin biosynthesis (Scheme 22). To test this, [6- C, 6-2H3]mevalonate was fed to 5-day old cultures and the resultant enriched austin isolated and its H, noise decoupled nmr spectrum determined. This showed clear isotopically shifted signals corresponding to the incorporation of two and mainly three deuteriums into the 12-, 13- and 14-methyl groups. The result for the 12-methyl group excludes the possibility of the involvement of (87) in austin biosynthesis. 

Carbon-13 NMR Analysis of Polyepichlorohydrin. Natural-abundance carbon-13 NMR spectra at 22.6 MHz were measured in benzene at 70°C. with proton noise decoupling, using a Bruker HFX-10 spectrometer equipped with a Nicolet 1085 Fourier transform spectroscopy accessory. 

Fig. 13. Proton-noise-decoupled 25 MHz i C-NMR spectrum of Neu5Ac dissolved in 2H2O, recorded at p H 2 and 25 °C. Only the signals stemming from the p-anomer are...

Fig. 13. Proton noise decoupled 25.2 MHz NMR spectrum of averufin (8) derived from [l,2- C]acetate. Spectral width 5000 Hz, pulse delay 1 sec 90° rf pulse (50 /isec) transients 20 K. Insert low power oflf-reasonance proton-decoupled partially relaxed spectrum. [From Gorst-Allman et al. (1977), 7. Chem. Soc. Perkin Trans. /, 2181-2188. Copyright permission from The Chemical Society, London.]...

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