Probing Aromaticity with Supersonic Jet Spectroscopy: A Case Study on Furan, Thiophene, and Selenophene

• Published in: The journal of physical chemistry letters 2024-11, Vol.15 (45), p.11445-11453
• Main Authors: Sahu, Akshay Kumar, Satpathi, Anant Ram, Rout, Saiprakash, Mohanty, Pranay, Dash, Laxmipriya, Biswal, Himansu S.
• Format: Article
• Language: English
• Subjects: Physical Insights into Light Interacting with Matter
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.4c02791

Aromaticity is a century-old concept that is even introduced in high school textbooks. However, the determination of the order of aromaticity of molecules as simple as furan, thiophene, and selenophene is still challenging. This work describes how different theoretical and experimental methods posit different aromaticity orders. To benchmark the theoretical results and arrive at a conclusion, mass-selective electronic and vibrational spectroscopy of these five-membered heterocycles under isolated supersonic-jet-cooled conditions was necessary. Since the aromaticity order can be unveiled from the magnitude of the electron density in the ring, we used hydrogen bonding as a probe. The experimental results revealed that selenophene forms the strongest π-hydrogen bond, suggesting that selenophene is the most aromatic, followed by thiophene and furan. It is concluded that gauge-including magnetically induced currents (GIMIC) and relative 1H and 13C NMR chemical shifts are better parameters to determine the aromaticity order in a similar class of molecules.