13C nuclear magnetic resonance of N-heterocycles. Part 3. 13C Chemical shift assignments of the carbonyl groups in penicillins and cephalosporins

Abstract

The ¹³C resonance frequencies of all the carbonyl carbon atoms in several penicillins and cephalosporins have been uniquely assigned for aqueous solutions by use of various experimental techniques. The ¹³C shift values are compared with other spectroscopic data (i.r. and X-ray). The possibility of interpreting the ¹³C results in terms of charge density distributions is discussed in relation to the mechanism of ring opening of the β-lactams by basic hydrolysis. For those compounds for which spectra have not been reported previously, the ¹³C frequencies of all the carbon atoms are assigned.