Gas-Phase Structure Determination of Dihydroxycarbene, One of the Smallest Stable Singlet Carbenes

Abstract

Carbenes are reactive molecules of the form R[superscript 1]-C̈-R[superscript 2] that play a role in topics ranging from organic synthesis to gas‐phase oxidation chemistry. We report the first experimental structure determination of dihydroxycarbene (HO-C̈-OH), one of the smallest stable singlet carbenes, using a combination of microwave rotational spectroscopy and high‐level coupled‐cluster calculations. The semi‐experimental equilibrium structure derived from five isotopic variants of HO-C̈-OH contains two very short CO single bonds (ca. 1.32 Å). Detection of HO-C̈-OH in the gas phase firmly establishes that it is stable to isomerization, yet it has been underrepresented in discussions of the CH[subscript 2]O[subscript 2] chemical system and its atmospherically relevant isomers: formic acid and the Criegee intermediate CH[superscript 2]OO. Keywords: atmospheric chemistry, carbenes, microwave spectroscopy, reactive intermediates, structure elucidation