ECD exciton chirality method today: a modern tool for determining absolute configurations

Area of Science:

• Chiroptical spectroscopy
• Computational chemistry
• Organic chemistry

Background:

• Exciton Chirality Method (ECM) is a popular approach for assigning absolute configuration (AC).
• It interprets Electronic Circular Dichroism (ECD) spectra of chiral compounds with multiple chromophores.
• The method relies on the exciton chirality rule correlating spectral signs with stereochemistry.

Purpose of the Study:

• To review the principles and applications of the ECM for AC assignment.
• To emphasize the prerequisites for correct ECM application.
• To discuss factors influencing exciton chirality and provide a molecular orbital perspective.

Main Methods:

• Quantum-mechanical (QM) calculations to verify prerequisites: molecular conformation and transition dipole moment (TDM) directions.
• Analysis of classic and recent literature examples of ECM applications.
• Discussion of geometrical parameters (angles α,β,γ) affecting couplet sign.

Main Results:

• The ECM is a powerful tool for determining AC when applied correctly.
• Key requisites include known conformation, TDM directions, and dominant exciton coupling.
• Geometrical parameters and QM calculations are crucial for accurate interpretation.

Conclusions:

• The ECM provides reliable AC assignments for diverse chiral molecules.
• Understanding conformational and electronic properties is vital for successful ECM implementation.
• This review consolidates ECM principles and applications, aiding researchers in configurational assignments.