Carbon 13 chemical shifts force constants

These extraordinary observations concerning the differences between the two sets of methylene protons, i.e. very different A s and opposite signs of the isotopic perturbations, could most easily be accommodated within a set of equilibrating bicyclobutonium ions [34]. Neither bisected cyclopropylcarbinyl cations [33] nor puckered cyclobutyl cations [35] are expected, among classical models, to have extremely different protons in their methylene groups. However, [34] has one pentaco-ordinated carbon whose attached hydrogens might have unusual chemical shifts and C—H bond force constants. 

Jones and co-workers used regression analyses to study the effects of field constants and resonance parameters (110) of some carbamate derivatives on their penetration and detoxication with some success (111). Similar studies have also been made by Fukuto and co-workers using selected oximes and their anticholinesterase activities (112). Kakeya et al. used chemical shifts and valence force constants in addition to other thermodynamic parameters in the structure-activity study of a series of sulfonamide carbonic anhydrase inhibitors (113). 

There is a relationship between the multiplicity of the metal-carbon bond and the carbonyl carbon shielding. This relationship is confirmed by the following there is a linear dependence of chemical shift on force constants / (CO) for W(CO)e L ... 

If it is assumed that there is no force constant difference and thus no equilibrium isotope effect between the P- and y-olefinic positions on [21], the different upheld shift observed for these carbons is due to different chemical shifts for the two positions in the frozen static spectrum. The isotopic exchange would then occur between a single populated downheld site, the a-position, having different vibrational force constants from the upheld side which has four times the population (the P,P and y,y -positions). The spectra indicate that the sum of the upheld shift of the two olehnic positions is half the size of the downheld shift of the deuteriated a-carbon when corrections for intrinsic shifts are taken into account. 

Using a variety of physicochemical parameters, Kakeya et al. have performed a structure-activity study on a series of sulfonamide carbonic anhydrase inhibitors. Hammett s o constants were found to vary linearly with pKa, chemical shift of the sulfamoyl protons, and the valence-force constant, fj., of the S=0 bond. It was found that compounds with a large a value, a large f- for the S=0 bond, and a large chemical shift for the sulfamoyl group showed a strong inhibitory activity for carbonic anhydrase this illustrates the importance of electronic effects in the activity of sulfonamide derivatives. ... 

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