19] Mechanistic studies utilizing oxygen-18 analyzed by carbon-13 and nitrogen-15 nuclear magnetic resonance spectroscopy

Abstract

Publisher Summary This chapter discusses the mechanistic studies utilizing 18 0, as analyzed by 13 C and 15 N nuclear magnetic resonance (NMR) spectroscopy. Specifically, the mechanistic studies covered include rates of hydrolysis reaction, the point of bond cleavage, and oxygen exchange reactions. Although the design of experiments involving reactions at carbon-oxygen bonds is largely dictated by the reaction being studied, considerable flexibility in the experimental design does exist. Reactions in which the carbon-oxygen bond is broken and reformed permit complementary experimental designs wherein the oxygen-18 isotope may be incorporated into the substrate or it may be present in the aqueous solvent. When 180 is incorporated into the substrate, the 18 0 label is replaced by 16 0 from the normal aqueous solvent as the reaction proceeds, and the label is essentially lost “irreversibly” to the bulk solvent, termed in the chapter as an out-exchange. An advantage to this experimental design is the conservation of the 18 O label. Utilizing NMR to study these reactions has the advantage that the reactions are assayed in a nearly continuous mode, sample handling is minimized, conversion to volatile derivatives is not necessary, and positional information is obtained directly.