Open AccessCorrelation between Optical Activity and the Helical Molecular Orbitals of Allene and Cumulenes
Author(s) -
Marc H. Garner,
Clémence Corminbœuf
Publication year - 2020
Publication title -
organic letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.94
H-Index - 239
eISSN - 1523-7060
pISSN - 1523-7052
DOI - 10.1021/acs.orglett.0c02980
Subject(s) - chemistry , chirality (physics) , molecular orbital , allene , axial chirality , optical rotation , circular dichroism , atomic orbital , cumulene , helicity , cotton effect , computational chemistry , molecular physics , stereochemistry , molecule , physics , enantioselective synthesis , organic chemistry , electron , symmetry breaking , chiral symmetry breaking , quantum mechanics , particle physics , nambu–jona lasinio model , catalysis
Helical frontier molecular orbitals (MOs) appear in disubstituted allenes and even- n cumulenes. Chiral molecules are optically active, but while these molecules are single-handed chiral, π-orbitals of both helicities are present. Here we computationally examine whether the optical activity of chiral cumulenes is controlled by the axial chirality or the helicity of the electronic structure. We exploit hyperconjugation with alkyl, silaalkyl, and germaalkyl substituents to adjust the MO helicity without altering the axial chirality. For the same axial chirality, we observe an inversion of the helical MOs contribution to the electronic transitions and a change of sign in the electronic circular dichroism and optical rotation dispersion spectra. While the magnitude of the chiroptical response also increases, it is similar to that of chiral cumulenes without helical π-orbitals. Overall, helical π-orbitals correlate with the big chiroptical response in cumulenes, but are not a prerequisite for it.