1,1,2‐Ethenetriol: The Enol of Glycolic Acid, a High‐Energy Prebiotic Molecule

Abstract

As low-temperature conditions (e.g. in space) prohibit reactions requiring large activation energies, an alternative mechanism for follow-up transformations of highly stable molecules involves the reactions of higher energy isomers that were generated in a different environment. Hence, one working model for the formation of larger organic molecules is their generation from high-lying isomers of otherwise rather stable molecules. As an example, we present here the synthesis as well as IR and UV/Vis spectroscopic identification of the previously elusive 1,1,2-ethenetriol, the higher energy enol tautomer of glycolic acid, a rather stable and hence unreactive biological building block. The title compound was generated in the gas phase by flash vacuum pyrolysis of tartronic acid at 400 8C and was subsequently trapped in argon matrices at 10 K. The spectral assignments are supported by B3LYP/6-311 ++ G(2d,2p) computations. Upon photolysis at l = 180-254 nm, 1,1,2-ethenetriol rearranges to glycolic acid and ketene.

Identification of Glycolaldehyde Enol (HOHC═CHOH) in Interstellar Analogue Ices

“…An identification of reactive intermediates such as enols is of particular importance to our understanding how sugars might form via molecular mass growth processes from the bottom up . However, considering the lack of suitable precursors and difficulty in preparation, simple enols represent one of the least explored classes of biorelevant organic molecules to date. − Consequently, gas-phase aldol reactions have also not been studied experimentally. 1,2-Ethenediol has, up to now, only been tentatively inferred as a possible byproduct in the fragmentation of the transition metal complex [HOCD 2 CD 2 OH···Zn 2+ ···OOCCH 3 ] and in an infrared and NMR study of the flash pyrolysis products of dihydroxy-11,12-ethano-9,10-dihydro-9,10-anthracene …”

Bottom-Up Synthesis of 1,1-Ethenediol (H2CC(OH)2)─The Simplest Unsaturated Geminal Diol─In Interstellar Analogue Ices

“…Since their postulation as tautomers of ketones in 1896 by Claisen, enolsalkenes carrying a hydroxyl group at a carbon–carbon double bondhave emerged as key reactive intermediates in molecular mass growth processes, such as carbohydrates in the formose cycle . Especially in low-temperature environments, such as cold molecular clouds like the Taurus Molecular Cloud 1 (TMC-1) and star forming regions such as Sagittarius B2 (Sgr-B2), the higher enthalpy of formation of enols compared to aldehyde and ketone counterparts decreases reaction barriers thus enabling (nearly) barrierless reactions that do not depend on the supply of external energy via galactic cosmic rays (GCRs) or ultraviolet (UV) photons . Enediolsalkenes carrying two hydroxyl groups at the same or both neighboring carbon atoms of the alkene moietyplay a critical role as reactive organic intermediates such as in the transformation of aldoses into ketoses as demonstrated by Lobry de Bruyn and Alberda van Ekenstein .…”

“…2 Especially in lowtemperature environments, such as cold molecular clouds like the Taurus Molecular Cloud 1 (TMC-1) and star forming regions such as Sagittarius B2 (Sgr-B2), the higher enthalpy of formation of enols compared to aldehyde and ketone counterparts decreases reaction barriers thus enabling (nearly) barrierless reactions that do not depend on the supply of external energy via galactic cosmic rays (GCRs) or ultraviolet (UV) photons. 3 Enediolsalkenes carrying two hydroxyl groups at the same or both neighboring carbon atoms of the alkene moietyplay a critical role as reactive organic intermediates such as in the transformation of aldoses into ketoses as demonstrated by Lobry de Bruyn and Alberda van Ekenstein. 4 Furthermore, 1,2-ethenediol (H(OH)CC(OH)H) has been contemplated as a key intermediate in the formation of complex sugars in the formose reaction thus showcasing the importance of enols in molecular mass-growth processes to biologically important molecules.…”

C2H5NO Isomers: From Acetamide to 1,2-Oxazetidine and Beyond

“…Some studies have explored the opposite approach, that is the formation of higher energy isomers from which lower energy species would emerge; 42 , 98 so, for example, Foo et al considered bimolecular (not of interest here) and unimolecular routes to acetamide—the latter from N -methyl formamide, acetimidic (ethanimidic) acid, 1-amino ethenol, and 2-amino acetaldehyde. 15 They show that the energy barrier for ( E,Z )-acetimidic acid → acetamide is 119 kJ mol –1 (this work, 130 kJ mol –1 ), while the barrier for anti -1-amino ethenol → acetamide is 170 kJ mol –1 ; the latter agrees well with values of 164 and 168 kJ mol –1 from Mardyukov 42 and this work, respectively.…”