Gas-phase structure determination of dihydroxycarbene, one of the smallest stable singlet carbenes

Abstract

Carbenes are reactive molecules of the form R1-C̈-R 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 CH2O2 chemical system and its atmospherically relevant isomers: formic acid and the Criegee intermediate CH2OO. A small stable singlet carbene: The geometric structure of dihydroxycarbene (HO-${\ddot {\rm {\rm C}}}$-OH) is experimentally determined using Fourier transform microwave spectroscopy. This carbene, a structural isomer of the simplest Criegee intermediate (CH 2OO) and formic acid (HCOOH), is found to be long-lived in the dilute gas phase because of the stabilizing effect of the two electron-donating hydroxy groups. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.