Understanding the Conformational Preference of Propeller-shaped Polycyclic Aromatic Hydrocarbons

25 November 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The physico-chemical properties of chiral propeller-shaped PAHs (propellerenes) are strongly dependent on their conformational behavior. A sound, physical model to understand why propellerenes exhibit a conformation preference for either a C2 or D3 conformation that moves beyond a phenomenological explanation is needed. We have therefore performed a computational study to rationalize the conformational preference of propellerenes. Using an activation strain analysis approach, we find that the conformational preference of propellerenes is ultimately determined by the flexibility of the wings. When wings are relatively flexible, as is the case for ortho-substituted propellerenes, a favorable contraction of the radial bonds connecting the core and the propellerene wings is possible, and the more distorted C2 conformation will be preferred. The more rigid wings of benzenoid propellerenes, on the other hand, cannot deform sufficiently, and will therefore always adopt a D3 conformation. Our approach represents a unique method to pinpoint the conformational preferences of propellerenes, and, in principle, any sterically congested molecule.


Polycyclic aromatic hydrocarbons
Conformational behavior
Activation strain model
Density functional theory

Supplementary materials

Understanding the Conformational Preference of Propeller-shaped Polycyclic Aromatic Hydrocarbons - Supplementary Information
Synthesis procedures, computational methods, NMR details, supplementary figures and tables, computed geometries.


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