===== On Searches for 1,3-Dihydroxypropanone and 1,2-Dihydroxypropanal in the ISM =====

The first report on the detection of [[molecules:ism:glycolaldehyd|hydroxyethanal]], CH<sub>2</sub>OHCHO, aka glycolaldehyde, in the interstellar medium was met with great enthusiasm as this molecule represents a more complex precursor to sugars than the ubiquitous methanal, H<sub>2</sub>CO, aka formaldehyde. Very recently, there has been a report on the detection of 1,3-dihydroxypropanone in Sgr B2(N-LMH):\\
S. L. Widicus Weaver and G. A. Blake,\\
**[[https://doi.org/10.1086/430407|1,3-Dihydroxyacetone in Sagittarius B2(N-LMH): The First Interstellar Ketose]]**\\
//Astrophys. J.// **624**, L33–L36 (2005);\\
**[[https://doi.org/10.1086/497963|Erratum]]**\\
//Astrophys. J.// **632**, L163 (2005).\\
A column density was derived that was very high: about a factor of three higher than that of H<sub>2</sub>CO – that seems rather peculiar.

One more recent paper seriously questions the findings mentioned above:\\
A. J. Apponi, D. T. Halfen, L. M. Ziurys, J. M. Hollis, A. Remijan, and F. J. Lovas,\\
**[[https://doi.org/10.1086/504979|Investigating the Limits of Chemical Complexity in Sagittarius B2(N): A Rigorous Attempt to Confirm 1,3-Dihydroxyacetone]]**\\
//Astrophys. J.// **643**, L29–L32 (2006).\\
No line was identified unambiguously. The upper limit derived for 1,3-dihydroxypropanone was lower than the column density derived above by a factor of about 300 and about a factor of four below that of hydroxyethanal. Moreover, it was pointed out that the column density of 1,3-dihydroxypropanone may be lower still by about a factor of six or so if the column density ratio 1,3-dihydroxypropanone : hydroxyethanal corresponds to that of hydroxyethanal : methanal. Even though this does not have to be correct this assumption is certainly reasonable.

Overall, we would recommend to view 1,3-dihydroxypropanone as not yet detected.

1,2-Dihydroxypropanal, aka glyceraldehyde, is an isomer of 1,3-dihydroxypropanone. It has been searched for unsuccessfully by:\\
J. M. Hollis, P. R. Jewell, F. J. Lovas, A. Remijan, and H. Møllendal,\\
**[[https://doi.org/10.1086/423200|Green Bank Telescope Detection of New Interstellar Aldehydes: Propenal and Propanal]]**\\
//Astrophys. J.// **610**, L21–L24 (2004).\\
The upper limit for 1,2-dihydroxypropanal is similar to that of 1,3-dihydroxypropanone in the paper above.


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Contributor(s): H. S. P. Müller; 05, 2006

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