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Correlation Between Optical Activity and the Helical Molecular Orbitals of Allene and Cumulenes

submitted on 04.09.2020, 09:59 and posted on 04.09.2020, 12:45 by Marc Hamilton Garner, Clemence Corminboeuf

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.


Independent Research Fund Denmark, case no. 9056-00009B


Email Address of Submitting Author


Ecole Polytechnique federale de Lausanne (EPFL)



ORCID For Submitting Author


Declaration of Conflict of Interest

No conflict of interest.