Validation and extension of the gas-phase superacidity scale

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Analytical Chemistry

Background:

• Discrepancies exist between experimental and computational gas-phase acidity (GA) values for strong acids.
• Previous experimental GA values for superacids require validation and extension.
• Accurate GA scales are crucial for understanding acid-base chemistry and reaction mechanisms.

Purpose of the Study:

• To validate and extend the superacidic portion of the gas-phase acidity scale.
• To resolve discrepancies between experimental and computational GA values.
• To provide a reliable experimental GA scale for strong acids.

Main Methods:

• Remesured the gas-phase acidity of strongly acidic compounds using equilibrium Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS).
• Introduced methodological improvements, including a novel anchoring approach.
• Anchored the scale to high-level computational GA values of trifluoromethanesulfonic acid and bis(fluorosulfonyl)imide.

Main Results:

• A new section of the gas-phase acidity scale comprising 20 superacids was established with high consistency (0.2 kcal/mol standard deviation).
• Experimental GA values are now in agreement with high-level theoretical calculations.
• Structure-acidity relationships were analyzed using the new data and existing acetonitrile (MeCN) and 1,2-dichloroethane (DCE) acidity data.

Conclusions:

• The methodological innovations employed are effective for accurate GA determination.
• Strong evidence supports the revised experimental GA values for strong acids.
• The study provides a more reliable gas-phase acidity scale for superacids.