Direct Spectroscopic Evidence for an n→π Interaction

• Published in: Angewandte Chemie International Edition 2016-06, Vol.55 (27), p.7801-7805
• Main Authors: Singh, Santosh K., Mishra, Kamal K., Sharma, Neha, Das, Aloke
• Format: Article
• Language: English
• Subjects: conformational analysis; electronic spectroscopy; gas-phase IR spectroscopy; supersonic jet
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201511925

The n→π* interaction is an extremely weak but very important noncovalent interaction. Although this interaction is widely present in biomolecules and materials, its existence is counterintuitive and so has been debated extensively. Herein, we have reported direct spectroscopic evidence for an n→π* interaction for the first time by probing the carbonyl stretching frequency in phenyl formate using isolated gas‐phase IR spectroscopy. This result also demonstrates that the conformational preference for the cis conformer of phenyl formate compared to the trans conformer arises due to the presence of the n→π* interaction in the former. The direct proof reported herein for this controversial but important noncovalent interaction should stimulate further experimental and theoretical investigation on this intriguing research topic. Here's the proof: Direct spectroscopic evidence for an n→π* interaction was provided for the first time by probing the carbonyl stretching frequency in cis and trans conformers of phenyl formate using gas‐phase IR spectroscopy. The cis form of the molecule, in which an n→π* interaction occurs, was found to be more stable than the trans isomer.