(7) A related use of quantitative 13C NMR as a mechanistic probe is described by Stothers and Nickon. J. Am. Chem. SOC., 94, 8581, 8582 (1972).(8) Conventional mass spectrometry is not particularly useful for detecting small amounts of nondeuterated (for example m-1) material in the presence of large m+ ions. Thus only a few cases (Table I, entries 5 and 18) allow a comparison of 13C NMR and MS methods. In these cases the agreement was ...