An alternative interpretation of the ultracold methylhydroxycarbene rearrangement mechanism: cooperative effects

Abstract

Recent studies have reported surprising results related to the rearrangement of carbenes under ultracold conditions, making use of sophisticated models of quantum tunnelling to explain the observed phenomena. Here, we demonstrate that a methylhydroxycarbene (H3C-C-OH) rearrangement is possible by making changes in molecularity (i.e., through cooperative effects), owing to intermolecular hydrogen bond/H-transfer. The model used for accomplishing these changes in molecularity suggests the occurrence of two chemical species during the rearrangement and preferential formation of acetaldehyde. We propose an alternative interpretation for the methylhydroxycarbene rearrangement, as well as for a bimolecular isomerization mechanism for acetaldehyde formation with an activation barrier, Ea, of +0.25 kcal mol(-1), relative to 1a′ (−8.06 kcal mol(-1) relative to 1a); this barrier is lower than that required by H-tunnelling as proposed by Schreiner et al. We also note that the mechanism for obtaining vinyl alcohol leads to the simultaneous formation of acetaldehyde through an Ea of +13.53 kcal mol(-1), relative to 1a (+0.93 kcal mol(-1) relative to 1b), again confirming the predominant presence of acetaldehyde.

Atmospheric Simulation Chamber Studies of the Gas-Phase Photolysis of Pyruvic Acid

“…Literature of pyruvic acid photolysis using such radiation typically can be separated into two categories. The first investigates the low-pressure (0–150 Torr of buffer gas) photochemistry of approximately 1 Torr of pyruvic acid, a concentration several orders of magnitude higher than would be expected in the lower atmosphere. − These studies, bolstered by computational work, − conclude that, following photon absorption, gas-phase pyruvic acid undergoes simultaneous concerted hydrogen atom transfer and decarboxylation with a quantum yield of unity. − The immediate products are carbon dioxide and a reactive intermediate, methylhydroxycarbene (CH 3 COH), which is observed as acetaldehyde (CH 3 CHO) following isomerization. − …”

Kinetics of low-temperature transitions and a reaction rate theory from non-equilibrium distributions

“…Temperature ranges for the validity of the approach are assessed with respect to features of the potential energy barrier to reaction [20,112], permitting comparison with experiments and tests against alternative formulations. Elementary reactions, widely investigated both experimentally and theoretically, which have been described successfully, are F + H 2 [28,96], F + HD [113], CH 4 + OH [20], CH 3 Cl + OH [20], H 2 + CN [20], and also abstraction and dissociation in the nitrogen trifluoride channels [114], and proton rearrangement in curcumin [115] and methylhydroxycarbene [116]. The deformed formulation has also been found useful to describe other reactions not involving tunnelling but showing non-negligible sub-Arrhenius behaviour, such as the C + CH + reaction [117], which is of relevance in cold interstellar clouds.…”

Beyond Boltzmann–Gibbs–Shannon in Physics and Elsewhere

“…Also worth mentioning are selected entropic applications beyond BG in other areas of knowledge: complex networks [ 16 , 17 , 18 ]; economics [ 149 , 150 , 151 , 152 , 153 , 154 , 155 , 156 ]; geophysics (earthquakes, atmosphere) [ 157 , 158 , 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 ]; general and quantum chemistry [ 139 , 167 , 168 , 169 , 170 , 171 ]; hydrology and engineering (water engineering [ 172 ] and materials engineering [ 173 , 174 ]); power grids [ 175 ]; the environment [ 176 ]; medicine [ 177 , 178 , 179 ]; biology [ 180 , 181 ]; computational processing of medical images (microcalcifications in mammograms [ 182 ] and magnetic resonance for multiple sclerosis [ 183 ]) and time series (e.g., ECG in coronary disease [ 184 ] and EEG in epilepsy [ 185 , 186 ]); train delays [ 187 ]; citations of scientific publications and scientometrics [ 188 , 189 ]; global optimization techniques [ 190 ...…”