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tokens: estimates of the relative abundances of the COMs detected in L1157-B1. With this goal in mind, we obtained their excitation conditions and column density carrying out a simple rotational diagram analysis. We computed the molecular abundances with respect to H 2 by using the whole CO column density in the B1 direction, as estimated by Lefloch etal. ( 2012 ), N (CO) = and assuming a standard relative CO abundance X (CO) = N (CO)/ N (H 2 ) = 10 4 . The obtained temperatures, column densities and abundances are summarized in Table 1 . The rotational diagrams of the newly detected COMs are shown in Fig. 2 . For all the detected species, the line emission can be reasonably well fitted by one single gas component whose rotational temperature is around 2030K (Table 1 ). Glycolaldehyde has a slightly larger rotational temperature (50K) but also a larger error bar (10K). Considering only the lines observed with E up , a lower rotational temperature () would provide a very good fitting. Figure 2. Rotational diagrams of COMs detected towards L1157-B1. From the top to bottom: C 2 H 5 OH, H 2 CCO, HCOCH 2 OH and CH 3 OCH 3 . The best fit is drawn by the red line. For HCOCH 2 OH, the fit to the transitions with is drawn by the blue dashed line. Column densities vary from 210 12 cm 2 (formamide) to 110 15 cm 2 (methanol). Incidentally, the column density of the other COMs shows a relatively small range of variation, from 2 to 510 13 cm 2 , namely less than a factor of 3. In other words, with the exception of formamide, which is significantly less abundant, the other detected COMs have abundances a factor of 2050 lower than methanol. We searched for acetic acid (CH 3 COOH), the other isomer of glycolaldehyde and methyl formate, using the frequencies given in Ilyushin, Kleiner Lovas ( 2008 ). We failed to detect it. We could place an upper limit on its abundance, adopting T rot similar to that of methyl formate () and glycolaldehyde (), and the partition function given by Calcutt etal. (in preparation). We obtain a 3 upper limit of 510 9 at (10 8 at ): Acetic acid is less abundant by a factor of 35 with respect to methyl formate. 3.3 Comparison with hot corinos When compared to other solar-like star-forming regions where these COMs were previously detected (IRAS 162932422: Jaber etal. 2014 ; Coutens etal. 2015 ; Jrgensen etal. 2016 ; IRAS 2A and IRAS 4A: Taquet etal. 2015 ), L1157-B1 appears to be a site were COMs are very efficiently produced. The molecular abundances are higher in the shock than in the hot corinos by a factor of 210, depending on the species. The dimethyl ether abundance measured in IRAS 162932422 is the only exception. We note that only relatively small COMs are detected in the shock region, whereas larger COMs, for example, propanone (CH 3 COCH 3 ) and ethylene glycol [(CH 2 OH) 2 ], are detected in the inner protostellar environments (e.g. Maury etal. 2014 ; Jrgensen etal. 2016 ) but not yet in the shock. More observational data from