Carbon coupling constants solvent 118

One of the propylene derivatives displays the same effects to a lesser degree. The propylene carbonate coupling constants are solvent invariant. 

Table 12.2.2. Calculated average values of dipole moment, four-bonds proton-carbon coupling constant and linkage rotation of p-D-maltose and p-D-mannobiose in different solvents at 25°C...

Instrumentation. H and NMR spectra were recorded on a Bruker AV 400 spectrometer (400.2 MHz for proton and 100.6 MHz for carbon) at 310 K. Chemical shifts (< are expressed in ppm coupling constants (J) in Hz. Deuterated DMSO and/or water were used as solvent chemical shift values are reported relative to residual signals (DMSO 5 = 2.50 for H and 5 = 39.5 for C). ESl-MS data were obtained on a VG Trio-2000 Fisons Instruments Mass Spectrometer with VG MassLynx software. Vers. 2.00 in CH3CN/H2O at 60°C. Isothermal titration calorimetry (ITC) experiments were conducted on a VP isothermal titration calorimeter from Microcal at 30°C. 

Compounds in which the carbons are sp3 hybridized display the same confused situation. Erickson 78> reports that the trans vicinal H—H coupling constant of c//-dibromosuccinic anhydride (which is reasonably rigid) varies from 2.5 Hz in CHC13 to 6.0 Hz in acetone and dioxane. The same paper reports that the meso dibromosuccinic anhydride and the two corresponding dichloro compounds do not display any solvent dependence of their coupling constants. (Erickson also reports that lJc.H of the dl- dibromide decreases from 172 Hz in chloroform to 166 Hz in acetone and 165 Hz in dioxane exactly the opposite behavior from that observed for any other 1JC H coupling ever studied). It is at least possible that these data result from chemical degradation of the solute rather than from true solvent effects as discussed here. 

The teirperature dependencies of the chemical shift values for both Cl and C4 were determined in four different solvents (water, dimethyl sulfoxide, methanol and dioxane) and are shown in Figures 8 and 9. The resonance for Cl at 298 C varied from 101.6 ppm in D2O to 104.0 ppm in methanol. The resonance for C4 at the same temperature varied from 75.3 ppm in dimethyl sulfoxide to 78.3 ppm in methanol. The most pronounced tenperature dependence is observed in water and dioxane, where Cl and C4 signals varied from 101.4 ppm to 101.9 ppm (Cl, water, 278-358 K) and from 75.7 ppm to 76.5 ppm (C4, dioxane, 288-360 K), respectively. Thus, both tenperature and solvent dependence of C shifts indicate different conformational behavior of the molecule at various physico-chemico conditions. This feature is manifested even more clearly by the dependencies of the three-bond proton-carbon J and J coupling constants (< ) - Hl -Cl -04-C4 and f = H4-C4-04-C1 ) which are plotted against tenperature in Figures 10 and 11. 

The spin-spin coupling constants for the spectrum of dibenzothiophene in carbon tetrachloride and acetone have been accurately determined by computer analysis and listed. In routine structural studies of derivatives of dibenzothiophene it is usually found that ortho-couplings are close to 8 Hz, meta couplings about 2 Hz and between 0.5 and 1 Hz. In chloroform-dj, H-2 and 3 in dibenzothiophene have the same chemical shift and the spectrum of 1,4-dimethyldibenzothiophene in this solvent also shows H-2,3 as a singlet at 87.03. Apart from the minimal coupling which has been detected between H-1,9 of 0.08 Hz, no interring coupling is observed in dibenzothiophenes. 

It has been shown that triphenyl(p-cyanobenzyl)phosphonium tetrafluoroborate (16), which exhibits a a LUMO level localized predominantly on the heteroatom and benzylic carbon, gives products derived from out-of-solvent cage chemical reactions on direct irradiation (reaction 6). This behaviour is connected with the nuclear hyperfine coupling constant of the heteroatom in triphenylphosphine radical-cation171. 

Using the data shown in Table 3.4, a linear plot of 13C versus 1H solvent shifts is obtained [92], Moreover, 13C solvent shifts correlate linearly with the one-bond carbon-13-proton coupling constants [92]. This is attributed to changes in the average distance of bonding electrons in the C — H bond of chloroform due to intermolecular association [92], Since much smaller solvent shifts of the carbon tetrachloride 13C resonance are found [92], interactions between chlorine and the solvent can be disregarded. Thus,... 

One-bond coupling constants JCH may suffer from slight solvent effects. Table 3.4 shows this behavior for chloroform, whose carbon-proton coupling increases with the polarity of the medium when measured in different solvents, being 208 Hz in cyclohexane and 215 Hz in pyridine [92]. This is attributed to association between chloroform and solvents susceptible to hydrogen bonding. 

The proton and carbon chemical shifts of twenty-one and twenty different anthocyanins are presented in Table FI. 4.4 and Table FI. 4.5, respectively. These anthocyanins are chosen to illustrate the chemical shifts of the majority of anthocyanin building blocks reported. The linkage positions of the various anthocyanin building blocks may be conspicuous through shift comparison. However, be aware of shift effects caused by variation in solvent, pigment concentration and temperature. Table FI.4.6 contains typical H- H coupling constants of the most common anthocyanidins. 

Early ESR studies demonstrated that the hyperfine coupling constant (ac 13) for 13C(car-bonyl)-substituted fluorenone radical anion is counterion-dependent. For the free ion, ac 13 = 2.75 Gauss. In contrast, when the counterion is Li+, ac 13 = 6.2 Gauss23. Consider Scheme 4 For the free ion, canonical structure 1 and 2 are contributors to the resonance hybrid. For the >C=0 / Li+ ion pair, association of Li+ with oxygen increases the relative contribution of canonical structure 1 to the resonance hybrid, resulting in greater spin density at carbon. The fact that spin (and charge density) varies as a function of counterion (and presumably solvent) will certainly affect the reactivity of the radical ion. However, very few quantitative studies exist which directly address this point. 

Figure 2.12 shows the carbon NMR spectrum for 1,2-dibromofluoroethane. As usual, the protons are decoupled, so that the only couplings that one can see are those between fluorine and carbon. Two signals are observed at 33.8 and 89.1 ppm, with one-bond and two-bond coupling constants of 257 and 23.5 Hz, respectively. (The multiplet at 77 ppm derives from the solvent, CDC13.)... 

Scheme 3.18 provides some pertinent proton and carbon chemical shift and coupling constant data for trihalomethanes, including what data are available for fluorodihalomethanes. There are potentially significant solvent effects on proton chemical shifts of all trihalomethanes,... 

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