Reversing Hydrogen Isotope Effect on the Rate of the Gas Phase Decomposition of Oxalic Acid

Reactive intermediates in 4He nanodroplets: Infrared laser Stark spectroscopy of dihydroxycarbene

“…Again, there is no evidence for the cis,cis-rotamer in He droplets, and there was also no evidence for it in the Ar matrix. 36 These observations are consistent with a unimolecular decomposition mechanism of oxalic acid, [68][69][70][71][72] in which a concerted hydrogen migration and C-C bond cleavage produces dihydroxycarbene and CO 2 . Assuming this mechanism, it is expected that the thermal extrusion of CO 2 from the cTc oxalic acid isomer produces trans,trans-HOCOH, whereas the cTt isomer decomposes to trans,cis-(see Fig.…”

“…The absence of the cis,cisrotamer is apparently due to the low internal energy content of gas-phase trans,cis-HOCOH, which cannot rotationally interconvert prior to being captured by a He droplet. These results strongly support the oxalic acid decomposition mechanism proposed by Lapidus et al [68][69][70][71] It is more difficult to rationalize the extent to which formic acid is produced in these experiments. In the Ar matrix study, Schriener et al reported a 1:5 ratio of dihydroxycarbene to formic acid upon pyrolysis of oxalic acid.…”

Infrared Spectroscopy of Molecular Radicals and Carbenes in Helium Droplets

“…The dipole components for trans,trans-and trans,cis-rotamers are (μ a , μ b ) = (0.00, 0.68 (6)) and (1.63(3), 1.50(5)), respectively. The IR spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid [92][93][94][95] and computations of HO COH torsional interconversion and tautomerization barriers [96].…”

Effects of Surface Coordination on the Temperature-Programmed Desorption of Oxalate from Goethite

“…The gas-phase thermal decomposition of oxalic acid has notably been described in great detail experimentally and theoretically. [38][39][40][41][42][43][44][45][46] Other work assessed the roles of different solvents on the thermal decomposition products of oxalate [47][48][49][50][51][52][53][54] including water 55 as well as the effects of metal ion complexation. 56 Metal-oxalate salts have also been studied and described extensively.…”

“…In the former complex, close interactions with desorbing OH and OH 2 moieties could promote proton transfer to desorbing carbonyl groups and lead to decomposition pathways characteristic of oxalic acid. [38][39][40][41] Inner-sphere metalcarbonyl interactions could, however, lead to decomposition pathways that are more characteristic of oxalate salts. 63,64 The dominant gas-phase thermal decomposition pathway of oxalic acid in the 400-430 K range typically produces equimolar concentrations of carbon dioxide and formic acid: [38][39][40][41] Decomposition pathways of metal-oxalate salts are substantially different from those of oxalic acid vapors.…”