Correlation Between Optical Activity and the Helical Molecular Orbitals of Allene and Cumulenes
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 Authormarc.firstname.lastname@example.org
InstitutionEcole Polytechnique federale de Lausanne (EPFL)
ORCID For Submitting Author0000-0002-7270-8353
Declaration of Conflict of InterestNo conflict of interest.
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in Organic Letters