Extraction of One-Handed Helical Frontier Orbital in Even [n]Cumulenes by Breaking Mirror Images of Right- and Left-Handed Helical Orbitals: Theoretical Study

摘要

Even [n]cumulenes with an even number n of double bonds are known to have degenerate helical frontier orbitals even in linear-chain structures. Theoretical analysis was conducted to separate one-handed helical orbitals from the others in cumulenes to determine their enantioselective chemical/physical properties. Donor ((NH2)(3)C-) and acceptor ((NO2)(3)C-) substituents separate the degenerate energy levels of right- and left-handed helical frontier orbitals in even [n]cumulenes. Lone pairs (LPs) in the donor group can interact with helical orbitals on the cumulene backbone, leading to "LP-helical orbital" interactions. A difference in the manner of interaction between left- and right-handed orbitals, depending on the LP direction, breaks the mirror symmetry between them. Consequent energy splitting between left- and right-handed orbitals results in extraction of a one-handed helical frontier orbital only. This is the first example of extracting a one-handed helical frontier orbital while maintaining sufficiently large energy splitting in even [n]cumulene in the framework of C-1 molecular symmetry by donor-acceptor substitutions.