The gas phase stability of carbanions centered at various positions on pyridine N-oxide were investigated by computational and experimental methods. In addition, G3MP2 computations were completed on ring-deprotonated pyridine and N-methylpyridinium. With these species, the effect of a nitrogen-centered positive charge on carbanion stability was assessed. Introduction of the nitrogenoxide group into the benzene ring decreases the ΔH acid by about 20 kcal/mol, but surprisingly, the effect is nearly independent of the position of the group (ortho, meta, or para). The results indicate that the N-oxide offers a balance of field, resonance, and local effects that cancels out any positional preferences. G3MP2 calculations indicate that a similar lack of positional selectivity is seen in nitrobenzene and benzonitrile. Overall, the data suggest that π-effects are limited in phenyl anions and as a result, ylide-like, rather than carbene-like, resonance structures are most important in the anions derived from ring deprotonation of arenes and heterocycles of these general types.

The rates and products from the gas-phase reactions of Co(III) salens with ethyl and t-butyl diazoacetate were examined. Addition with loss of N(2) is observed, and substituent effects as well as DFT calculations indicate that addition is rate determining. Calculations suggest that the carbene species involve novel structures with the carbenic carbon bridging between the cobalt and a salen oxygen. Collision-induced dissociation leads to an unusual, bridged metal/ketene species.