A general method to predict optical rotations of chiral molecules from their structures

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• The direct relationship between a molecule's absolute configuration and its chiroptical response (optical rotation) is not well-established.
• Predicting optical rotation based on molecular structure is crucial for understanding stereochemistry and molecular properties.

Purpose of the Study:

• To report a general rule for predicting the sign of optical rotation in chiral molecules with an RCHXY structure.
• To establish a predictive model based on absolute configuration and electronic properties of functional groups.

Main Methods:

• Utilized the Hammett constant (σp) to quantify the electron withdrawing/donating power of functional groups.
• Developed a priority list of functional groups based on their electron withdrawing strengths.
• Applied a model where the lowest priority group's position dictates the prediction based on the arrangement of the other three.

Main Results:

• A predictive rule was established for determining dextrorotatory or levorotatory properties.
• The rule correlates clockwise or counterclockwise arrangement of prioritized functional groups (from most to least electron withdrawing) with optical rotation sign.
• Exceptions to the general rule are noted, requiring careful application.

Conclusions:

• The proposed rule offers a method to predict optical rotation sign from absolute configuration for RCHXY chiral molecules.
• This work provides a valuable tool for chemists studying stereochemistry and chiroptical properties.
• The use of Hammett constants offers a quantitative basis for predicting optical rotation.