Cycloalkanes chemical shifts

Table 2.12. chemical shifts (relative configurations of cycloalkanes, pyranoses and alkenes (application of y-effects) The shifts which are printed in boldface reflect y-effects on C atoms in the corresponding... 

While the comparison of the OMTS and the (CH2)12 spectra helped to learn something about the kind of information solid state chemical shifts can provide, we can obtain much more detailed data about the correlation of chemical shifts and the rotational isomeric states from the spectra of larger cycloalkanes. Usually conformational shift variations are discussed by (i) the so called y-gauche effect and (ii) the vicinal gauche effect, Vg 15) ... 

Table 4 13C NMR chemical shifts of ring carbon atoms of some spiro(cycloalkane-1,2 -[1,2,4]triazolo[1,5-c]pyrimidine carbonitriles measured in DMSO-d6 solutions...

Empirical additive substituent increments obtained by analysis of substituted alkanes, alkenes, cycloalkanes, aromatic and heteroaromatic compounds have proved to be useful for the prediction of 13C chemical shifts. These substituent increments will be tabulated for the various classes of organic compounds in Section 4.13. 

Table 4.4. 13C Chemical Shifts and One-Bond Coupling Constants JC H of Cycloalkanes (c5c in ppm) [206].

Fig. 4.1. Plot of UC chemical shifts of cycloalkanes versus ring size [206].

Table 4.10. 13C Chemical Shifts of Alkenes [90, 232-235], Dienes [233] and Methylene-cycloalkanes [236] (Sc in ppm).

Although proton spectra are not very useful for identification purposes, 13C nmr spectra are very useful. Chain-branching and ring-substitution normally cause quite large chemical-shift changes, and it is not uncommon to observe 13C shifts in cycloalkanes spanning 35 ppm. Some special features of application of 13C nmr spectra to conformational analysis of cycloalkanes are described in Section 12-3D. 

Sn chemical shifts (ppm) for some diorganostanna-cycloalkanes and -thiocycloalkanes... 

Cycloalkanes and Saturated Hetero-cyclics The chemical shifts of the CH2 groups in monocyclic alkanes are given in Table 4.7. The striking feature here is the strong shift to the right of cyclopropane, analogous to the shift of its proton absorptions. 

Table 2.12.13C chemical shifts (5C) and relative configurations of cycloalkanes, pyranoses and alkenes (application of y-effects)4 8. The shifts which are printed in boldface reflect y-effects on C atoms in the corresponding --------------------------------------------------isomer pairs---------------------------------------------------... 

EXAMPLE 6.10 Predict the chemical shift of the hydrogens in the cycloalkanes below. For the purposes of this problem you may assume that the rings are planar, though actually they are not ... 

TABLE 7.1 13C Chemical Shifts for Common Alkanes and Cycloalkanes"... 

Table 14.1 illustrates that absorptions for a given type of C-H bond occur in a narrow range of chemical shift values, usually 1-2 ppm. For example, all sp hybridized C-H bonds in alkanes and cycloalkanes absorb between 0.9 and 2.0 ppm. By contrast, absorptions due to N-H and O-H protons can occur over a broader range. For example, the OH proton of an alcohol is found anywhere in the 1-5 ppm range. The position of these absorptions is affected by the extent of hydrogen bonding, making it more variable. 

The chemical shift tables presented below illustrate the carbon resonances of both the ring carbons of substituted forms and the shifts of the side chain carbons of alkyl cycloalkanes. 

The bond lengths in thiolane (tetrahydrothiophene) are the same as those in dialkyl sulfides. As in tetrahydrofuran (see p 67), the ring is nonplanar and conformationally flexible. The twist conformation is, however, preferred because of the larger heteroatom. The activation energy for pseudorotation is greater than that for tetrahydrofuran. The chemical shifts in the NMR spectrum correspond to those observed for cycloalkanes and dialkyl sulfides. 

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