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Cation-π interactions in protonated phenylalkylamines.
Barbara Chiavarino1, Maria Elisa Crestoni, Markus Schütz
1Dipartimento di Chimica e Tecnologie del Farmaco, Università degli Studi di Roma La Sapienza , P. le A. Moro 5, I-00185 Roma, Italy.
The Journal of Physical Chemistry. A
|July 26, 2014
Summary
Protonated phenylalkylamines were studied using infrared photodissociation spectroscopy. Stable, folded structures stabilized by cation-π interactions were identified for higher homologues, confirming theoretical predictions.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Phenylalkylamines are a class of organic compounds with potential applications in various chemical fields.
- Understanding the gas-phase structures and conformations of protonated amines is crucial for elucidating their chemical behavior.
Purpose of the Study:
- To investigate the gas-phase structures of protonated phenylalkylamines (C6H5(CH2)nNH2, n = 1-4).
- To determine the preferred conformations and identify stabilizing interactions in these protonated species.
- To validate the use of Infrared Multiphoton Dissociation (IRMPD) spectroscopy combined with computational methods for structural analysis.
Main Methods:
- Electrospray ionization (ESI) to generate protonated phenylalkylamine ions in the gas phase.
- Infrared Multiphoton Dissociation (IRMPD) spectroscopy using free electron laser and OPO/OPA laser sources.
- Density Functional Theory (DFT) calculations for predicting stable conformers and vibrational frequencies.
- Analysis of experimental IRMPD spectra and comparison with calculated spectra.
Main Results:
- Protonated benzylamine (n=1) exists as a single stable conformer.
- Higher homologues (n=2-4) exhibit multiple accessible conformations.
- The most stable conformers for n=2-4 are characterized by intramolecular cation-π interactions, where the ammonium group interacts with the aromatic ring.
- These folded structures are confirmed by matching experimental IRMPD spectra with DFT-calculated spectra.
Conclusions:
- The study successfully characterized the gas-phase structures of protonated phenylalkylamines.
- Cation-π interactions play a significant role in stabilizing the preferred folded conformations of longer-chain homologues.
- The combination of IRMPD spectroscopy and DFT calculations is a powerful approach for conformational analysis of protonated organic molecules.
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