Chiral Self Recognition: Interactions in Propylene Oxide Complexes.

Area of Science:

• Computational chemistry
• Molecular interactions
• Chiral recognition

Background:

• Propylene oxide dimer exhibits homochiral and heterochiral structures.
• Understanding chiral recognition requires analyzing subtle energetic effects.

Purpose of the Study:

• Elucidate the energetic origins of chiral recognition in propylene oxide dimers.
• Investigate the accuracy of various computational methods in predicting these energy differences.

Main Methods:

• High-level electronic structure calculations, including coupled-cluster with single, double, and perturbative triple excitations (CCSD(T)) up to the complete basis set limit.
• Symmetry-adapted perturbation theory (SAPT) and functional-group SAPT (F-SAPT) analyses.
• Comparison of benchmark interaction energies with approximate methods (DFT, wave function-based).

Main Results:

• Benchmark calculations reveal subtle energy differences between diastereomeric propylene oxide structures (RRn-RSn).
• Approximate computational methods often struggle to accurately predict the sign and magnitude of these diastereomeric energy differences.
• SAPT analyses identify electrostatic and dispersion contributions as primary drivers of the observed energy differences.
• Chiral interactions induce significant shifts and splittings in vibrational frequencies, particularly in the torsional mode.

Conclusions:

• Chiral recognition in propylene oxide dimers is governed by subtle energetic effects, primarily electrostatic and dispersion interactions.
• Accurate prediction of these effects requires high-level computational methods; many approximate methods are insufficient.
• Chiral interactions measurably impact molecular vibrational frequencies, offering a potential avenue for experimental discrimination.