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to rotation in the parent amide are 18^20 kcal/mol (Table III). In imidate anions the greater double-bond character, as evidenced by the Vtrans of 1.5 Hz, ought to increase the barrier substantially. Therefore the mechanism for E/Z interconversion is not rotation, but nitrogen inversion. (Similar reasoning has been used previously to draw the same conclusion regarding imidate esters.33)Substituent and medium effects are as expected. The substituent effect at carbon has generally been considered to be small, on the basis of Hammett p values34 and MO calculations.35 Our results show that even the strong donor, -O', does not change the inversion barrier substantially, relative to imines (e.g., Me2C-NPh, AG* = 20.336) or imidate esters (e.g., MeC(0-p-tol)=NMe, AG* = 20.233). As for nitrogen substituents,37 phenyl lowers the barrier to inversion because it can delocalize the 2p lone pair of the transition state. The bulky terf-butyl also lowers the barrier because interference with either formyl CH or -0" destabilizes the ground state.With iV-phenylformimidate anion it was also possible to demonstrate qualitatively a solvent effect on the inversion barrier. Although two stereoisomers were seen in protic solvents, only one set of NMR signals was seen in Me2SO-d6. This is not due to a predominance of a single stereoisomer (as in THE), since the kinetics of base-catalyzed exchange suggested that the two stereoisomers should be present in comparable amounts (Table II). Indeed, the chemical shifts observed in the aromatic region were consistent with a 3:1 mixture of E and Z forms, in rapid equilibrium. Apparently the barrier for iV-phenylformimidate anion is so low in Me2SO-d6 that only an

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Laser desorption Fourier transform mass spectra (LD-FTMS) of a variety of nonvolatile polymer additives are compared with fast atom bombardment spectra (FAB) of the same materials. Both a pulsed carbon dioxide laser and a neodymlum-YAG laser with outputs of 10.6 and 1.064 Mm, respectively, were used to obtain LD-FTMS spectra of all samples. Three sterlcally hindered phenols and other additives containing a variety of functionalities Including thloester, phosphite, phosphonlte, and hindered amine groups were examined. In general, FAB spectra show undesirably large amounts of fragmentation, while molecular Ion species dominate LD-FTMS spectra. It Is concluded that LD-FTMS spectra are superior to FAB spectra for analysis of these common polymer additives.

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