Top panel: abundances of CH₃OCH₃ relative to CH₃OCHO versus the bolometric luminosity. Middle panel: abundances of C₂H₅CN relative to C₂H₃CN versus the bolometric luminosity. Bottom panel: abundances of C₂H₅CN relative to CH₃CN versus the luminosity. The dashed black line represents the fit to the data and the grey shaded area represents a factor 5 scatter from the fit. Our data points are represented in blue, the high-mass protostars (Belloche et al. 2016; Widicus Weaver et al. 2017; Coletta et al. 2020; Nazari et al. 2022) are represented with a star. The low-mass protostars are presented with crosses (Oya et al. 2017; Jørgensen et al. 2018; Belloche et al. 2020).