Spectroscopic Distinction of Different Carbon Bases: An Insight from Theory.

Spectroscopic differentiation based on the (13)C NMR chemical shift of the parent and protonated derivatives of carbon(II) and carbon(0) bases has been proposed. The (13)C chemical shift of the central carbon atom of carbenes in their parent and protonated forms will experience more downfield shift, whereas the central carbon atom of carbones will experience a lesser downfield shift; such shifts for compounds that possess "hidden" carbon(0) characteristics will lie between these two extremes. The (13)C chemical shifts of the protonated derivatives are solely dependent on the out-of-plane pπ occupancies of the central carbon atom. This difference arises due to their unique difference in bonding and may provide an easier distinction between these two classes of compounds.