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The N-Bromo-Hammick Intermediate
Virinder Bhagat1, J Philipp Wagner1,2
1Institut für Organische Chemie, Eberhard Karls Universität Tübingen, Auf der Morgenstelle 18, Tübingen, 72076, Germany.
Abstract:
We report the characterization of bromopyridin-2-ylidene, the N-bromo-Hammick intermediate, isolated in solid neon at 4.4 K. Computations (B2PLYP, NEVPT2), IR, and UV/vis spectroscopy characterize this intermediate as a singlet carbene with a vacant σ*-type frontier orbital. This unusual electronic structure (σ2σ*0) allows the carbene to isomerize to its more stable pyridine tautomer via a planar transition state, avoiding the deviation from planarity seen in other singlet carbenes. The compound's reaction with molecular hydrogen faces a minor but prohibitive barrier (8.4 kcal mol-1) at the low temperatures of the experiment.
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