Coupling constant data

Qualitative relaxation-studies have also been reported for an extensive series of derivatives of inositols, pentopyranoses, l,6-anhydro-/3-D-hexopyranoses, furanoses, and septanoses. In all instances, the experimentally determined Ri(ns) values reflect the anticipated geometry. For the furanose derivatives especially, they provide a better means for distinguishing between epimeric pairs than the relatively ambiguous interpretation of coupling-constant data. 

Specific coupling constant data will be provided for each class of fluo-rinated molecules as they are discussed in Chapters 3-6. 

Although the spectra of fluorine containing compounds are non-exceptional, other than for the F—H coupling, and are highly predicable, typical proton chemical shift and coupling constant data will be provided within each chapter for each class of fluoroorganic compound. 

Chemical shift and coupling constant data for carbons in the vicinity of fluorine substituents will be provided for the various classes of fluo-roorganic compounds discussed in the next four chapters. 

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. 

H and13C NMR Data for Halofluoroalkanes. Scheme 3.13 provides some pertinent proton and carbon chemical shift and coupling constant data for fluorochloro- and fluorobromomethanes, whereas Scheme 3.14 contains relevant data for some typical halo fluoroalkanes. There does not appear to be anything unusual going on here. 

H and13C NMR Data. The data given in Scheme 3.39 provide some guidelines for proton and carbon NMR chemical shift and coupling constant data for fluoroalkenes. Notice that in all cases, hydrogens that are cis to the fluorine substituent are deshielded relative to those that are trans. 

Proton and Carbon NMR Data. Some selected chemical shift and coupling constant data from proton and carbon spectra of chloro- and bromofluoroethylenes are presented in Scheme 3.46. 

Some typical proton and carbon chemical shift and coupling constant data for allylic and benzylic systems are given in Scheme 3.54. An alkenyl substituent or a phenyl substituent on either a CH2F or a —CHF- group has virtually no effect upon that carbon s chemical shift, and they also only affect the proton chemical shift by about 0.5 ppm. 

Carbon and Proton NMR Data. 13C and 11NMR chemical shift and coupling constant data for 2-fluoropyridine, 2-fluoroquino-lines, and 2-fluoroquinoxoline are provided in Scheme 3.62. 

Typical examples of such spectra, those of 1,1-difluorobutane and 2,2-difluoropentane, are given in Figs. 4.8 and 4.9, respectively. The chemical shift and F—C coupling constant data for each are given below the respective spectra. 

Examples of fluorine chemical shift and coupling constant data are given in Scheme 5.56. Note the significant four- and five-bond F—F and F—H coupling in these compounds, which no doubt is due in part to through-space coupling. 

Classical shielding arguments indicate an electron-rich phosphorus atom, or equally, an increase in coordination number. The silicon atom seems also to be electron-rich, while the carbon has a chemical shift in the range expected for a multiply bonded species. The coupling constant data are difficult to rationalize, as it is not possible to predict the influence of orbital, spin-dipolar, Fermi contact, or higher-order quantum mechanical contributions to the magnitude of the coupling constants. However, classical interpretation of the NMR data indicates that the (phosphino)(silyl)carbenes have a P-C multiple bond character. 

Coupling constant data (Hz) for silicon derivatives of triethylphosphines... 

A revised structure for the secoiridoid xylomollin (176) has been proposed on the basis of lH coupling constant data and the revised trans-fused arrangement was confirmed by crystallographic analysis (78JA7079). Both rings are in a chair conformation and the bridgehead hydrogen atoms are disposed trans to each other. 

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