Doubly protonated benzene in the gas phase

Area of Science:

• Physical Chemistry
• Computational Chemistry

Background:

• Doubly protonated benzene dications are key intermediates in chemical reactions.
• Understanding their structure and fragmentation is crucial for reaction mechanism elucidation.

Purpose of the Study:

• To investigate the structural properties and unimolecular fragmentation pathways of doubly protonated benzene.
• To determine the proton affinities of protonated benzene at different positions.

Main Methods:

• Tandem-mass spectrometry was employed to study unimolecular fragmentations.
• Electron ionization of 1,3- and 1,4-cyclohexadienes generated the dications.
• Density functional theory calculations were used for comparison.

Main Results:

• Electron ionization of 1,3-cyclohexadiene yields the singlet state, while 1,4-cyclohexadiene yields singlet and triplet states.
• Fragmentation exclusively occurs via dehydrogenation to form the benzene dication.
• Proton affinities were determined for meta, ortho, and para positions.

Conclusions:

• The study elucidates the fragmentation mechanisms and structural aspects of doubly protonated benzene.
• Experimental findings show good agreement with theoretical calculations, validating the computational approach.