The newly synthesized C18 ring is demonstrated as the smallest all-carbon acceptor that exhibits strong electron acceptance. This study provides a quantum-chemical investigation of the electron-acceptance behavior of monocyclic carbon rings with a particular emphasis on C18 through the formation of a dative bond with piperidine. The results show that Cn rings form strong dative bonds with piperidine, whereas the respective van der Waals (vdW) complexes are higher in energy. The main driving force is the release of angle strain of cyclo[n]carbons caused by the change in hybridization from sp to sp2 associated with the formation of the dative bond. On the contrary, other sp allotropes, diynes, favorably form vdW complexes. Molecular dynamics (MD) simulations support the stability of the dative bond throughout a simulation of 20 ps. This opens up the possibility of stabilizing highly reactive C18 through dative/covalent functionalization.

Institute of Organic Chemistry and Biochemistry Academy of Sciences of the Czech Republic v v i Flemingovo nám 2 16000 Prague 6 Czech Republic

Regional Centre of Advanced Technologies and Materials Czech Advanced Technology and Research Institute Palacký University Křížkovského 511 8 77900 Olomouc Czech Republic

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Striking Impact of Solvent Polarity on the Strength of Hydrogen-Bonded Complexes: A Nexus Between Theory and Experiment

The stability of covalent dative bond significantly increases with increasing solvent polarity