Determining Inversion Barriers in Atrop- isomers – A Tutorial for Organic Chemists

Abstract

Dynamic behavior is a fascinating property of natural and artificial systems and its understanding has significantly impacted the transformation of molecular interchanges into controlled molecular motion. In this tutorial, the key descriptors of enantiomeric stability are examined in-depth. Enantiomerization and racemization are discussed and differentiated on a fundamental level proposing a unified and distinct nomenclature. Their mathematical meanings and relations are described and deduced cohesively in the context of atropisomerization. The calculation of inversion barriers from thermodynamic and kinetic data is demonstrated and the interdependences between the latter are explained mathematically. Using current examples from our group, the determination of rate constants and the thermodynamic parameters is shown in a step-by-step manner using the most common techniques. The tutorial is concluded with aspects and considerations concerning statistical data analysis and error determination of measurements including a practical guide to Monte-Carlo simulations.

Molecular dynamic staircases: all-carbon axial chiral “Geländer” structures

“…In a second series an enantiopure sample was exposed to different temperatures and the concentrations of both enantiomers were analyzed after different periods by chiral HPLC giving access to thermodynamic parameters like the enthalpies Δ H ≠rac and entropies Δ S ≠rac of the racemization process. 28 …”

Carbo[n]helicenes Restricted to Enantiomerize: An Insight into the Design Process of Configurationally Stable Functional Chiral PAHs

“…As the racemization is as tatistical process of irreversible transformationo ft he enantiopure (or enantioenriched)s ample into an optically inactive racemic mixture, the rate constant for the racemization can be obtained by av ariety of spectroscopic and chromatographic techniques. [26,27] While the rate constant of racemization (k r )d escribes the rate of for-mationo faracemic mixture, the rate constant of enantiomerization (k e )r efers to the rate of interconversion of enantiomers. When one molecule transforms into the other enantiomer,t he enantiomeric excessi sr educed by two molecules.…”

“…[28] There are, however, inconstancies and discrepancies in the literature whether k r or k e ,a sw ell as k = 1o rk = 0.5 should be used in the Eyring equation. [26,29,30] Therefore, in the following sections, whenever the original data are available DG°(T)w as recalculated with k e and k = 0.5 Prince Ravat obtained his PhD in 2014 from the Max Planck Institute for Polymer Research, Mainz, Germany,f ollowed by ap ostdoctoral stay at the Universityo fB asel, Switzerland. Thereafter,h em oved to the Universityo f Tokyo, Japan,t ow ork as aJ SPS postdoctoral fellow.I n2 018, he started his independent research group at the University of Würzburg within the "ExcellentI deas" program.…”

A Chiral Polycyclic Aromatic Hydrocarbon Monkey Saddle

“…[10c] To estimate the inversion barrier for the racemization, we measured its velocity by time-dependent CD spectroscopy at different temperatures (see also Supporting Information). [16] Using an Arrhenius plot (Supporting Information, Figure S72) the calculated inversion barrier is 104 AE 4 kJ mol À1 and fitting the one calculated by DFT (B3LYP/6-311G(d,p)) for the stepwise mechanism via twisted transition states (Figure 3). The half-life of 6 at room temperature is one day (t 1/2 = 23 AE 1 h).…”