Gas-Phase Reactivity of Quinoline-Based Singlet Oxenium Cations

Area of Science:

• Physical Organic Chemistry
• Mass Spectrometry
• Computational Chemistry

Background:

• Quinolyloxenium cations are reactive intermediates whose gas-phase chemistry remains underexplored.
• Understanding the electronic structure and reactivity of such cations is crucial for various chemical applications.

Purpose of the Study:

• To generate and characterize isomeric quinolyloxenium cations in the gas phase.
• To investigate the reactivity of these cations with various nucleophiles and substrates.
• To elucidate the electronic ground state and structural properties of quinolyloxenium cations.

Main Methods:

• Generation of quinolyloxenium cations using an ion trap mass spectrometer.
• Structure elucidation via collision-activated dissociation (CAD) experiments on model compounds.
• Computational studies employing CASPT2/CASSCF(16,14)/cc-pVTZ//CASSCF(16,14)/cc-pVTZ calculations.

Main Results:

• Lack of radical reactions indicates closed-shell singlet electronic ground states for the cations.
• Calculations confirm singlet ground states are significantly lower in energy than excited states.
• Cations display strong electrophilicity, reacting exothermically with nucleophiles (e.g., dimethyl sulfide) and undergoing hydride abstraction with cyclohexane.

Conclusions:

• Quinolyloxenium cations possess stable singlet ground states and exhibit pronounced electrophilic character.
• Reactions with nucleophiles occur preferentially at electron-deficient carbon atoms in the benzene ring.
• Hydride abstraction by the oxygen atom is a key reaction pathway, highlighting the cation's unique reactivity.