Editing Acetaldehyde (section)

===Tautomerization to vinyl alcohol===
[[File:Ethanal Ethenol Tautomerie.svg|thumb|left|upright=1.3|Tautomeric equilibrium between acetaldehyde and vinyl alcohol.]]{{clear left}}

Like many other [[carbonyl compound]]s, acetaldehyde [[tautomer]]izes to give an [[enol]] ([[vinyl alcohol]]; IUPAC name: ethenol):

:{{chem2|CH3CH\dO  <->  CH2\dCHOH}} {{spaces}} {{spaces}} {{spaces}} {{spaces}} {{spaces}} {{spaces}} {{spaces}} {{spaces}} ∆''H''<sub>298,g</sub> = +42.7 kJ/mol

The [[equilibrium constant]] is 6{{e|−7}} at room temperature, thus that the relative amount of the enol form in a sample of acetaldehyde is very small.<ref>{{Cite journal | doi = 10.1021/ja00168a035| title = Keto-enol equilibrium constants of simple monofunctional aldehydes and ketones in aqueous solution| journal = Journal of the American Chemical Society| volume = 112| issue = 12| pages = 4862–8| year = 1990| last1 = Keeffe | first1 = J. R.| last2 = Kresge | first2 = A. J.| last3 = Schepp | first3 = N. P.}}</ref> At room temperature, acetaldehyde ({{chem2|CH3CH\dO}}) is more stable than [[vinyl alcohol]] ({{chem2|CH2\dCHOH}}) by 42.7 kJ/mol:<ref>Johnson, R.D. III "CCCBDB NIST Standard Reference Database". nist.gov</ref> Overall the keto-enol tautomerization occurs slowly but is catalyzed by acids.

Photo-induced keto-enol tautomerization is viable under [[Atmosphere|atmospheric]] or stratospheric conditions.  This photo-tautomerization is relevant to the Earth's atmosphere, because vinyl alcohol is thought to be a precursor to [[carboxylic acid]]s in the atmosphere.<ref>{{Cite journal | doi = 10.1038/nchem.1052| pmid = 21602858| title = Near-threshold H/D exchange in CD<sub>3</sub>CHO photodissociation| journal = Nature Chemistry| volume = 3| issue = 6| pages = 443–8| year = 2011| last1 = Heazlewood | first1 = B. R. | last2 = MacCarone | first2 = A. T. | last3 = Andrews | first3 = D. U. | last4 = Osborn | first4 = D. L. | last5 = Harding | first5 = L. B. | last6 = Klippenstein | first6 = S. J. | last7 = Jordan | first7 = M. J. T. | last8 = Kable | first8 = S. H. | bibcode = 2011NatCh...3..443H}}</ref><ref>{{Cite journal | doi = 10.1126/science.1220712| pmid = 22903524| title = Photo-Tautomerization of Acetaldehyde to [[Vinyl alcohol|Vinyl Alcohol]]: A Potential Route to Tropospheric Acids| journal = Science| volume = 337| issue = 6099| pages = 1203–6| year = 2012| last1 = Andrews | first1 = D. U.| last2 = Heazlewood | first2 = B. R.| last3 = MacCarone | first3 = A. T.| last4 = Conroy | first4 = T.| last5 = Payne | first5 = R. J.| last6 = Jordan | first6 = M. J. T.| last7 = Kable | first7 = S. H.| bibcode = 2012Sci...337.1203A| s2cid = 42079807}}</ref>