Proton-Decoupled Spectra

Compound 1 contains one phosphorus atom, so that the broad-band proton decoupled spectrum is extremely simple it consists of only one line at 8.5 ppm. This spectrum is shown in Fig. 22, together with the proton-coupled spectrum. 

Further evidence for the occurrence of the degenerate rearrangement in these compounds was obtained by NMR spectroscopy. The Z-form of 3-p-chlorophenyl-5-( -j -chlorophenyl- -[ N-amino])vinylisothiazole (171) showed in the non-proton-decoupled spectrum a double triplet for the amino nitrogen and a singlet for the heterocyclic ring nitrogen. It confirms that 171 is in fact an equilibrium mixture of 171 and 172 (Scheme IV.67). 

Q Assign the signals for the proton-decoupled spectrum of paracetamol (Figure 4.36),... 

Figure 1. P-31, broad-hand, proton-decoupled spectrum of RhCl(ttp) in the presence of a twentyfold molar ratio of Et3Al in toluene. The (CH30)3P0 signal is the secondary standard, which is superimposed on...

FIG. 20. Two-dimensional resolved C spectrum of n-hexane recorded with the technique indicated in Fig. 19. Twenty-two experiments were co-added for each of the 64 values of t, between 0 and 35 ms. Resolution is severely limited by the 64 x 64 data matrix used to represent the two-dimensional Fourier transform. The absolute values of the Fourier coefficients are plotted. The undecoupled one-dimensional spectrum is indicated along the oi, axis, and the proton-decoupled spectrum is shown along the ujj axis. From ref. 157. 

FIG. 26. The high-field regions of spectra of l-dimethylamino-2-melhylpropene. (a) Proton-decoupled spectrum, (b)-(d) Multiplet sub-spectra corresponding to the three methyl resonances P, Q, and R respectively, (e) Full proton-coupled spectrum, showing overlapping and interference from acetone-df, and tetramethylsilane. From ref. 23. 

The contour plot of the C,H-HSC spectrum of 2-chlorobu-tane is shown in Figure 13.5, where the F (vertical) axis corresponds to H chemical shift and the F2 axis to C chemical shift. Note that the normal H spectrum [5 1.01 (t, 3H), 1.52(d, 3H), 1.72, m,2H), 3.96 (m, IH)] is plotted vertically along the left side of the 2D spectrum, while the proton-decoupled spectrum is plotted horizontally along the top. 

Recall how we could use the small satellites present in a H spectrum to determine the magnitude of one-bond C-H coupling constants (Section 8.6.1). Now we will need to use satellites in the proton-decoupled spectrum to map out all one-bond couplings This will not be easy,... 

Figure 13.17. a) Simulated expansion of signal 4 of the proton-decoupled spectrum of 2-chlorobutane. (b) Simulated ID INADEQUATE spectrum of the same signal. 

Figure 5-17 Lower The normal proton-decoupled spectrum of cholesteryl acetate. Upper The attached proton test (APT), phased so that CHt and quaternary carbons are positive and CH and CH3 carbons are negative. (Reproduced with permission from A. E. Derome, Modern NMR Techniques for Chemical Research Pergamon Press, Oxford, UK, 1987,...

The 100 MHz C-13 spectrum of amoxicillin trihydrate in D20 at pD 8 is shown in Figure 5. The lower trace is the full proton decoupled spectrum and the upper trace is the DEPT 135 spectrum in which signals from the quaternary carbons are suppressed. Chemical shifts relative to external dioxan at 67.4 ppm and assignments are ... 

Figure 15.21 Proton decoupled spectrum of ethylbenzene. Each carbon atom gives a single signal consisting of a singlet. These simpler broad band, decoupled spectra yield less information.

Coupling to H can be deactivated using proton broadband decoupling techniques. The respective notations are P-NMR for the proton coupled spectrum, and P- H -NMR for the proton decoupled spectrum. This notation is analogous to that used in C-NMR spectroscopy. 

Figure 5.11. C-NMR proton-decoupled spectrum of 3-methyl-1-phenelhyl-4-piperidone in CDCtj at...

Figure 5.12. C-NMR proton-decoupled spectrum of (A) c %-2,6-dimethyl- A-methyl-4-piperidone, and (B) c s/trans-2,6-dimethyl-Tti-methyl-4-piperidone in CDClj at 22.5 MHz (carbonyl resonances not...

Figure 5.13. C-NMR spectra of a cis (2-Mej3-Ar) I2,3-lrimethyl-3-arylpiperidine hydrochloride (Ar = m-methoxyphenyl) in CDClj. Upper proton-decoupled spectrum lower off-resonance spectrum.

An example of an aromatic fluorine-containing compound can be found in Figure 7.7, where we have recorded the 19F spectra (both proton coupled and decoupled) of p-fluoroacetophenone. Once again we find a singlet for the fluorine atom in the proton-decoupled spectrum and a complex multiplet for the fluorine atom in the proton-coupled spectrum. The fluorine atom couples differently to the ortho and meta protons in this para-substituted compound. Coupling constants for proton-fluorine can be found in Appendix F of Chapter 4. 

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