Protonation Isomer Specific Ion-Molecule Radical Reactions

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Computational Chemistry

Background:

• Distonic-radical ions are key intermediates in various chemical processes.
• Understanding the influence of protonation site on reactivity is crucial for reaction mechanism elucidation.
• Gas-phase studies offer a simplified environment to isolate specific chemical effects.

Purpose of the Study:

• To independently measure the gas-phase reaction kinetics of quinazoline cation protonation isomers with ethylene.
• To investigate the impact of protonation site variations on radical reactivity.
• To elucidate the underlying factors, particularly electrostatic effects, governing these reactivity differences.

Main Methods:

• Ion-mobility filtering was used to separate protonation isomers.
• Laser-equipped quadrupole ion-trap mass spectrometry enabled kinetic measurements.
• Double-hybrid density functional theory was employed for theoretical calculations.

Main Results:

• Distinct gas-phase reaction kinetics were observed for the two protonation isomers.
• Protonation site variations led to significant changes in radical reactivity towards ethylene.
• Through-space electrostatic interactions were identified as the primary driver of reactivity differences.

Conclusions:

• The location of protonation on the quinazoline cation profoundly influences its radical reactivity.
• Electrostatic effects, mediated by through-space interactions, are critical in determining reaction outcomes.
• Advanced computational methods are necessary to accurately model and explain these long-range effects in radical reactions.