While the existence of dimethylketene in ISM has not been proven to date, the presence of related molecules including parent ketene and methylketene, and their role as potential intermediates in the generation of prebiotic molecules has been demonstrated. Both enol 2 and ketene 4 have the capacity to form isobutyric acid 3 (Scheme 1), although neither of these molecules has been generated or characterized thus far. Following the approach adopted in prior studies, we report here the generation of 2 alongside 4 via pyrolysis of dimethylmalonic acid (1) as the precursor. The resulting molecules are subsequently captured in an argon matrix at a temperature of 3.5 K and characterized by IR and UV/vis spectroscopy and quantum chemical computations. Enediol 2 was synthesized through the thermal decarboxylation of 1. This thermochemical process involved evaporating 1 at a temperature of 80 °C and subjecting it to pyrolysis in a quartz tube heated to 750 °C. We determined that the ideal pyrolysis temperature for enol generation is 750 °C; concurrently a significant amount of 4 forms as well. The pyrolysis products were subsequently condensed onto a cold matrix window at a temperature of 3.5 K, utilizing an abundant excess of argon as the condensing medium. Under these conditions, several characteristic bands were easily discernible in the spectroscopic analysis. Notably, the asymmetric CO2 stretching vibration at 2343 cm -1 , the vibrational signatures corresponding to water and compound 3, and additional infrared bands attributed to 2 were readily identifiable (Figure ). The identification of 3 was verified through a comparison with a matrix-isolated IR spectrum of an authenticated sample. When subjected to irradiation at 254 nm, matrix-isolated 2 underwent [1,3]H-shift leading to 3. This transformation resulted in the disappearance of all IR absorption signals associated with 2. Simultaneously, new IR bands emerged, corresponding to isobutyric acid (3) (Fig. ). The experimental IR spectrum of 2 exhibits a remarkable concordance with the computed IR spectrum of 2 obtained with B3LYP/def2-TZVP computations. After repeating the experiment using deuterated d2-1, the bands observed in d2-2 are also in good agreement with the computed spectrum; the isotopic shifts agree well. Specifically, the stretching vibration of the C=C bond exhibited a red-shift of 5 cm -1 (calculated: 14 cm -1 ) in d2-2. Analogously, the stretching vibrations of the OH groups in d2-2, at 2986 cm -1 and 2949 cm -1 , were red-shifted by 662 cm -1 and 681 cm -1 , respectively (calculated: 684 cm -1 and 730 cm -1 ). The good agreement between experimentally measured and computed shifts provides compelling evidence for the successful synthesis of 2. In the pyrolysis IR spectrum, we also identified bands corresponding to 4. The characteristic IR band at 2129 cm -1 (computed: 2183 cm -1 ) corresponds to the CCO stretching vibration of 4 (Figure ). The UV/Vis absorption spectrum of 2 displays a broad transition at 190 nm, in agreement with the computed TD-DFT spectrum that gives λmax = 192 nm. This absorption band originates from a HOMO-LUMO+3 excitation, which correlates with a π→π* transition. In congruence with the IR experiments, the 190 nm band diminishes upon exposure to irradiation at 254 nm (Fig. ). As previously mentioned, pyrolysis led to the formation of 4 through the elimination of water from the enol in the gas phase. Unlike the enol tautomer of propionic acid, the generation of the enol from the precursor requires high activation energy (Ea = 31.1 kcal mol -1 computed at B3LYP/def2-TZVP), contributing to the formation of 4. Subsequent irradiation (l = 254 nm) revealed the formation of propene (5). The distinct band at 1027 cm -1 can be assigned to the C=C wagging mode of 5; likewise, additional vibrations can be attributed to 5 (Figure ). One question revolves around the mechanism of formation for 5, whether it occurs through a concerted mechanism from 4 or via a facile 1,2-H-shift from elusive dimethyl carbene (6), which may form through photochemical decarbonylation of 4. To date, only one free alkyl carbene has been characterized, namely 2-adamantyl carbene. In a previous examination of the rearrangement of 6 to propene, Evanseck and Houk theoretically estimated the activation energy for the 1,2-H-shift reaction to be 4.7 kcal mol -1 . This low-energy process is probably also accompanied by some quantum mechanical tunneling (QMT) as suggested for the 1,2-hydrogen shift in methylchlorocarbene (in solution), a conclusion that would probably also hold for pure alkyl carbenes, thereby making their isolation even more challenging. As deuteration should slow QMT quite significantly, we also used d6-1 in an attempt to isolate d6-6, which, however, remained elusive, despite a somewhat higher computed barrier of 7.7 kcal mol -1 . To gain deeper insight into the thermochemistry of 2, we performed computations on the potential energy profile around 2 at DLPNO-CCSD(T)/cc-pVQZ//B3LYP/def2-TZVP + ZPVE at 0 K (∆H0). Our computations reveal that 2 can exist in three distinct conformations, characterized by the orientations of the OH groups relative to the opposing C-O bond. These conformations are referred to as: s-cis, s-trans 2ct, s-trans, strans 2tt and s-cis, s-cis 2cc. Among these conformers, 2ct is the most stable, with 2cc and 2tt being higher in energy by 0.7 and 2.0 kcal mol -1 (Fig. ), respectively. The conformational isomerization from 2ct to 2tt involves an activation energy (TS1) of 3.6 kcal mol -1 , while the activation energy for the 2ct to 2cc rotamerization is 4.5 kcal mol -1 (TS2). In our FVP experiments, 2ct is the predominant conformer in the matrix. This is likely due to rapid QMT rotamerization, which is typical for OH groups. From the 2tt conformer, propionic acid conformer 3t can be generated through a [1,3]H-shift, which is associated with an activation barrier of 50.8 kcal mol -1 (TS3). The tautomerization from 2ct to 3c (the most thermodynamically stable conformer) involves an activation barrier of 51.3 kcal mol -1 (TS4). Apart from keto-enol tautomerization to 3c, 2ct can also dehydrate into 4 (4 + H2O) through transition state TS5, with an energy barrier of 47.2 kcal mol -1 . As expected, under our pyrolysis reaction conditions, 4 readily formed. Figure reveals the emergence of 5 most likely originating from a concerted mechanism involving both a [1,2]H-shift and CO release from the ketene through TS6, featuring an activation barrier of 91.2 kcal mol -1 . Given that this formation exclusively depends on irradiation and is associated with an excessively high activation barrier, it is apparent that 5 is exclusively accessible photochemically. It is also possible for the ketene to undergo a conversion to singlet carbene 1 6, releasing CO upon photoexcitation. Carbene 1 6 reacts to form propene through a 1,2 H-shift (TS7), facilitated by its low activation barrier 7.7 kcal mol -1 (which is also prone to QMT, vide supra). We can therefore not differentiate between the two photochemical paths and 6 remains elusive.