Quantitative 13C Analysis

Quantitative 13C NMR is desirable in two situations. First in structure determinations, it is clearly useful to know whether a signal results from more than one shift-equivalent carbon. Second, quantitative analysis of a mixture of two or more components requires that the area of the peaks be proportional to the number of carbons atoms causing that signal. 

There are two reasons that broadband-decoupled l3C spectra are usually not susceptible to quantitative analysis  

FIGURE 4.7 Inverse gated proton decoupling pulse sequence. Rd is relaxation delay, 0 is a variable pulse angle, t2 is the acquisition time. 

FIGURE 4.8 (a) Standard ll decoupled 13C spectrum of diethyl phthalate with relaxation delay (/ ,/) 7), 

The definition of chemical shift equivalence given for protons also applies to carbon atoms interchangeability by a symmetry operation or by a rapid mechanism. The presence of equivalent carbon atoms (or coincidence of shift) in a molecule results in a discrepancy 

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