Intramolecular structural characterization was
performed on the products of a thermally induced
enediyne cyclization of 1,2-bis((2-ethynylphenyl)
ethynyl)benzene (1). Enediynes exhibit a variety of
radical cyclization processes known to compete
with traditional Bergman cyclizations (11, 12),
thus often rendering numerous products with complex
structures that are difficult to characterize using
ensemble techniques (13). To directly image these
products with subnanometer spatial resolution, we
thermally activated the cyclization reaction on an
atomically clean metallic surface under ultrahigh
vacuum (UHV). We used STM and nc-AFM to
probe both the reactant and final products at the
single-molecule level. Our images reveal how the
thermally induced complex bond rearrangement
of 1 resulted in a variety of unexpected products,
from which we have obtained a detailed mechanistic
picture—corroborated by ab initio density
functional theory (DFT) calculations—of the cyclization
processes.