Resonance warfarin

A structural application of 13C nmr, which shows its power in an area where H nmr is indecisive, is shown in Figure 9-48. Here, we see the high-field 13C resonances of a substance known variously as Coumadin, or the sodium salt of warfarin, 14, which is used widely as a blood anticoagulant in the treatment of diseases such as phlebitis. It also has substantial utility as a rat poison because of its anticoagulant action. 

There is no indication of any abnormality in the chemical shifts of carbons 11, 12, and 14 shown in Figure 9-48a. Furthermore, there is a downfield resonance 216.5 ppm from the carbons of TMS (not shown in Figure 9-48a) which is typical of a C=0 carbon corresponding to C13. When 14 is treated with acid, we expect the product (warfarin) of structure 15 to be formed, which should have a 13C spectrum much like that shown in Figure 9-48a ... 

Figure 9-48 Proton-decoupled, 3C nmr spectrum at 15 Mu7 nf th upfield region of (a) the sodium salt of warfarin (14) showinn nn L Uh side the resonances of C11, C12, and C14. This part of the spectrum ran be compared with the more complete spectrum (b) of warfarin itQJJ (16 and 17). The gaggle of evenly spaced sharp peaks toward the rlJ of the spectrum arises from the solvent, 0(CD2CD2)20. n er...

It is important not to confuse the properties of tautomerism and resonance. They are quite different effects and the differences between them are summarised in Table 3.1. Although the enol form of warfarin is present to... 

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