n → π* Interaction Enabling Transient Inversion of Chirality

Area of Science:

• Physical Chemistry
• Quantum Mechanics
• Spectroscopy

Background:

• Acrolein dimer exists in different isomeric forms.
• Hydrogen bonds and n → π* interactions influence molecular structure and stability.
• Chirality inversion is a known quantum mechanical phenomenon, typically involving proton motion.

Purpose of the Study:

• To observe and characterize isomers of the acrolein dimer.
• To investigate the role of n → π* interactions in molecular dynamics.
• To explore novel instances of chirality inversion beyond proton motion.

Main Methods:

• High-resolution rotational spectroscopy was employed.
• Experiments were conducted in pulsed jets for precise molecular isolation.
• Spectral features, including quadruplets, were analyzed to understand molecular motion.

Main Results:

• Two acrolein dimer isomers were identified and characterized.
• The energetically favored isomer features stabilizing hydrogen bonds and a planar configuration.
• A second isomer, with a dominant n → π* interaction, exhibits a concerted tunneling motion leading to transient chirality inversion of heavy moieties.

Conclusions:

• The study reveals a previously unobserved phenomenon of heavy moiety chirality inversion.
• n → π* interactions are shown to facilitate complex molecular dynamics, including tunneling.
• This finding expands the understanding of quantum mechanical principles in molecular systems.