Protons, carbon-attached, chemical shift values

Table 8.1 Approximate chemical shift values for non-aromatic protons attached to carbon...

Multinuclear NMR data for homologous senes of fluoromethylated malo-nates [72] and trimethylsilanes [97] are compiled in Table 11. In both senes, fluoromethyl attachment is to a quaternary site These compounds are readily synthesized using fluorohalomethanes to incorporate the final fluoromethyl moiety All the malonates, except diethyl methyltnfluoromethylmalonate (4) [93], are isopropyl-substituted diethyl esters [72]. The silane data, with the exception of trimethyltrifluoromethylsilane (5) [95], are from reference 97 Chemical shift data are very comparable, with the malonates having higher proton and fluorine chemical shifts but slightly lower carbon values. The magnitudes of cf and 2J jp coupling are similar for both sets of compounds. 

Suzuki and co-workers <68CPB750> have correlated chemical shift values of protons attached to the carbon at different sites in thiazolo[5,4-J]pyrimidine with the ease of substitution of halogen in 2,5,7-trichlorothiazolo[5,4-J]pyrimidine. The order of reactivity of chlorine was thus concluded to be C-2 > C-5 > C-7 which is the order of chemical shift protons at C-2 resonate at lower field than those at C-5, and C-7 protons resonate at highest field. It seems, however, that the reactivity at C-5 and C-2 is very similar as compound (175) reacts with hydrazine hydrate to yield a mixture of the isomers (176) and (177) (Equation (15)) <79IJC307>. 

XH chemical shifts. More detailed chemical shift data for a wide range of proton environments is given in Appendix 3, Tables A3.1, A3.3 and A3.4. In particular the chemical shift values quoted in Table A3.1 show that an electronegative substituent in aliphatic systems causes a downfield shift the greater the electronegativity the more substantial the shift. When two substituents are attached to the same carbon atom there is a greater downfield shift, but not as great as the sum of the two substituents separately. The approximate position of absorption in such cases can be predicted on the basis of the empirical parameters shown in Appendix 3, Table A 3.2. 

Thus the ecgonin methyl ester fragment J can clearly be recognised only the link to the O atom still remains to be established. The attachment of the 0 atom is identified by the large chemical shift value (S j = 5.59) of the proton on the same carbon atom. The parts A and J then give the skeleton K of cocaine. 

The chemical shifts of protons attached to the lithium-bearing carbon in alkyllithium compounds are found at high fields, as expected. A few representative chemical shift values are listed in Table IX (13, 14, 18, 23, 43, 44). Spin-spin couplings involving the protons have been utilized in assigning the isomers in vinylic systems (44). 

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