Schematic representation of the results from this paper: the discussed molecules are grouped according to their D/H ratios and excitation temperatures. The species underlined can be shown to have lower ¹²C/¹³C ratios by a factor 2 than typical values for the local ISM (although only tentatively for methyl formate and ethanol), while the remainder are either consistent with a standard ISM ratio or have too optically thick lines of the main isotopologuefor a reliable independent estimate.