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Solid‐State Structure of Protonated Ketones and Aldehydes
Author(s) -
Stuart Daniel,
Wetmore Stacey D.,
Gerken Michael
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201710263
Subject(s) - chemistry , oxonium ion , aldehyde , protonation , electrophile , acetaldehyde , anhydrous , ketone , photochemistry , benzaldehyde , acetone , medicinal chemistry , organic chemistry , catalysis , ion , ethanol
Protonated carbonyl compounds have been invoked as intermediates in many acid‐catalyzed organic reactions. To gain key structural and electronic data about such intermediates, oxonium salts derived from five representative examples of ketones and aldehydes are synthesized in the solid state, and characterized by X‐ray crystallography and Raman spectroscopy for the first time. DFT calculations were carried out on the cations in the gas phase. Whereas an equimolar reaction of the carbonyl compounds, acetone, cyclopentanone, adamantanone, and acetaldehyde, with SbF 5 in anhydrous HF yielded mononuclear oxonium cations, the same stoichiometry in a reaction with benzaldehyde resulted in formation of a hemiprotonated, hydrogen‐bridged dimeric cation. Hemiprotonated acetaldehyde was obtained when a 2:1 ratio of aldehyde and SbF 5 was used. Experimental and NBO analyses quantify the significant increase in electrophilicity of the oxonium cations compared to that of the parent ketones/aldehydes.