Calculating Optical Rotatory Dispersion Spectra in Solution Using a Smooth Dielectric Model.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Accurate calculation of molecular specific rotation is crucial for understanding chiral molecules in solution.
• Coupled cluster (CC) methods offer high accuracy for electronic structure calculations.
• Continuum dielectric models are commonly used to approximate solvent effects.

Purpose of the Study:

• To investigate the accuracy of coupled cluster (CC) methods combined with a continuum dielectric model for calculating specific rotation.
• To assess the performance of these methods for molecules with varying solvent responses.
• To identify limitations in current theoretical approaches for predicting solvation effects on optical properties.

Main Methods:

• Utilizing coupled cluster (CC) level calculations.
• Employing a continuum dielectric model with permittivity as a function of electron density.
• Polarizing Hartree-Fock (HF) molecular orbitals before coupled cluster singles and doubles (CCSD) calculations.
• Testing on (S)-methyloxirane, (1S,4S)-norbornenone, and (S)-2-chloropropionitrile.

Main Results:

• CCSD calculations yielded an incorrect sign for the specific rotation of (S)-methyloxirane in water.
• The continuum model failed to predict variations in optical rotatory dispersion (ORD) curves for nonpolar solvents.
• Computed solvent shifts for norbornenone and 2-chloropropionitrile were not of the correct magnitude.

Conclusions:

• Current CC methods with implicit solvent models struggle to accurately predict specific rotation and ORD.
• The solvent response significantly impacts solvation effects, which are not fully captured by simple continuum models.
• Further development of solvation models is needed for accurate theoretical predictions of chiroptical properties.