Enhanced Acidity of Fluorinated Ethanol on Water Microdroplets Accelerates CO 2 Capture

Comprehensive Summary Water microdroplets provide a unique environment that facilitates chemical reactions at the air‐water interface. Here, we provide mass spectrometric evidence that several types of fluorinated ethanol increase their acidity and undergo efficient deprotonation at the air–water interface of microdroplets, generating anions that capture CO 2 to form stable fluoroethoxyformate products. While increased fluorine substitution enhances the acidity by stabilizing conjugate bases through electron‐withdrawing effect, it simultaneously reduces the nucleophilicity of the bases by delocalizing their negative charges from oxygen atoms. This correlation between acidity of fluorinated ethanols and nucleophilicity of their conjugate bases results in monofluorinated ethanol exhibiting the highest reactivity toward CO 2 . Our results elucidate how fluorine substitution modulates anion reactivity and provide a strategy for CO 2 capture in microdroplets where the acidity of various substances could be greatly increased.