13C-NMR data

Structure of Oxy-F Compound F is extremely unstable and is difficult to obtain at a level of purity suitable for NMR studies. However, an oxidation product, Oxy-F, formed when F is left standing at — 20° C, is considerably more stable than F and can be purified to a sufficiently high level of purity. Oxy-F is nonfluorescent and shows absorption maxima at 237 nm and 275 nm (shoulder). The high-resolution FAB mass spectrum indicated the molecular formula of Oxy-F to be C33H3809N4Na2 [m/z 703.2363 (M + Na)+ and 681.2483 (M + H)"1"]. The H and 13C NMR data allowed the assignment of structure 7 to oxy-F (Fig. 3.2.6 Nakamura et al., 1988). 

The 13C NMR data for representative three-membered sulfones and sulfoxides are given in Table 5. The chemical shifts of the sp3-hybridized a-carbon in the parent thiirane70 and the five-membered ring86 sulfide, sulfoxide and sulfone are 18.1, 31.7, 54.3 and 51.1, respectively, whereas those of cyclopropenone, diphenylcyclopropenone and dimethylcyclopropenone are 169.087, 148.788 and 157.9, respectively. 

Degrees of polymerization can be calculated from quantitative 13C NMR data by considering the number of substituted (reacted) relative to unsubstituted (not yet reacted) ortho and para phenolic carbons where [5] is the sum of substituted ortho and para carbons and [5] + [f/ is the total ortho and para carbons. The fraction of reacted ortho and para sites is denoted by fs [Eq. (7.2)]. Thus, the number-average number of phenol units per chain Or) can be calculated using Eq. (7.3). This leads to a simple calculation of Mn = x x 106 — 14 ... 

Subsequent tables cover important titration methods (Table 17), useful 13C-NMR data for the analysis of LAB/LAS (Table 18), molecular fragments of alkylbenzenes (Table 19), and characteristic infrared absorption bands of an LAB/LAS molecule (Table 20). 

The H and 13C NMR data for the three metal derivatives were similar. An X-ray crystallographic structure for the gallium derivative (Fig. 6) indicated a shortened Ga—C (carbene) distance of 1.935(6) A, whereas the Ga—C(Me) distances had normal single bond values, 1.994(8) and 1.988(8) A. Thus, the structure may be visualized as being composed of the two canonical forms... 

Gelsevirine (2) was first isolated in 1953 from G. sempervirens as a minor component (3). Its structure was later elucidated on the basis of mass spectrometry as well as H-NMR and 13C-NMR studies (4). Gelsevirine has been found to be the predominant alkaloid in G. rankinii (24), and it was claimed that some of the previously reported 1 H-NMR and 13C-NMR data should be revised. Thus the previous assignments of H-16, H-15, H-14a, H-14e, and H-6 for gelsevirine should be changed to H-15, H-14a, H-16, H-6, and H-14e, respectively, from the evidence of the more accurate homonu-clear 2D COSY experiments. Similarly, from the heteronuclear 2D correlation spectrum, the assignments for C-16, C-15, C-6, and 1V-CH3 should be revised to C-15, C-16,1V-CH3, and C-6, respectively. 

The 13C-NMR data of koumine (18) and its derivatives 38 and 45 are all in agreement with the proposed structures. The rationalization of the mass spectra of koumine and its derivatives 38, 44, 39, 40, and 47, regarding the probable fragmentation pathway, is shown in Scheme 11. 

Figure 4 13C NMR data from concentrating the solutions from Experiments I and II.

H and 13C NMR Data. The examples in Scheme 3.3 provide insight into expected proton and carbon chemical shift and coupling constant data for primary alkyl fluorides. It can be seen that the influence on both proton and carbon chemical shifts diminishes rapidly as one moves away from the site of fluorine substitution. 

Characteristic 1H and 13C NMR Data. The examples in Scheme 3.7 provide relevant proton and carbon chemical shift data. 

H and 13C NMR Data. Pertinent proton and carbon NMR data, in addition to those given above, are provided in Scheme 3.9. Again, the increase in one-bond F—C coupling constant observed in the... 

H and 13C NMR Data. The carbons at the (3-position of a,(3-unsaturated carbonyl compounds are also deshielded relative to ordinary terminal fluoroalkenes (Scheme 3.52). 

C NMR Data. Some typical carbon NMR data are given in Scheme 3.73 for acid fluorides and for carbonyl fluoride. 

H and 13C NMR Data. The H chemical shifts of CF2H protons of difluoromethyl ethers lie between 6.00 and 6.3 ppm, with a significantly enhanced F—H two-bond coupling constant of around... 

C NMR Data. Some carbon NMR data for OCF2Cl groups and others bearing two heteroatoms are provided in Scheme 4.23. 

H and 13C NMR Data. A ketone or aldehyde carbonyl group bound to a CF2H group shields its proton slightly (0.1 ppm), and even more surprisingly, it also has a shielding effect upon its carbon chemical... 

H and 13C NMR Data. The ester function of ethyl difluoroac-etate deshields the CF2H proton slightly (about 0.1 ppm), whereas as was the case for ketones and aldehydes, it shields the carbon of either a CF2H or a CF2-alkyl group significantly (by about lOppm) (Scheme 4.37). 

Pertinent H and 13C NMR data are included, where available, in Schemes 4.43 and 4.44. As expected, trans F—H coupling is character-... 

H and 13C NMR Data. Typical proton and carbon NMR data for a,(3-unsaturated carbonyl compounds with a terminal vinylic CF2 group are given in Scheme 4.50. The pertinent F—H coupling constants have been given in the previous Scheme 4.49. Conjugation with a carbonyl group deshields the (3-CF2 carbon by 4-5 ppm. 

H and 13C NMR Data. The protons of allylic CF2H groups are deshielded by the vinylic group to the extent of 0.2 ppm, and its carbon is shielded by about 2 ppm. The carbons of allylic secondary CF2 groups are shielded to the extent of about 4 ppm (Scheme 4.53). 

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