Schematic (not to scale) of summarising the possible formation pathways and chemical links between the iCOMs (Sect. 5.1) and their emission origins (Sect. 5.2) within a GMC. The temperatures reported are averaged over the region but there can be variation from one region to another. We assume the size of a GMC is comparable or larger than the size of the ALCHEMI beam of 1.6″ (or ∼27 pc). Formation and chemical links: Sputtering from the ice grain mantle and gas phase formation pathways are both possible to explain the iCOM emission at GMC scales, whilst at SSC scales, the dust temperature can be high enough to allow thermal desorption. CH₃CHO and C₂H₅OH can also be chemically linked (i) both on the grain (with CH₃CHO as the precursor of C₂H₅OH) or via the Ethanol tree in the gas phase (with C₂H₅OH as a precursor for CH₃CHO). CH₃NH₂ and CH₂NH could be chemically linked (ii) by sharing similar precursors, both on the grain or in the gas phase (if the gas temperature is higher than 100 K; e.g. Halfen et al. 2013). Origin: At the scale of GMCs, the iCOMs are likely tracing large-scale shocks, due to either cloud-cloud collision (1) or shocks related to star formation activity (scenario 2a; see also Huang et al. 2023). At pSSC scales, iCOMs could trace either star formation-related heating process (scenario 2b; CH₃NH₂, NH₂CHO) and shocks (scenario 2a; CH₃CHO, CH₂NH, C₂H₅OH), associated or not (i.e. if cloud-cloud collision, scenario 1) with star formation.