Statistical (i.e. taking into account the statistical ratios for the functional groups with multiple H-atoms) CH₂ DOH (top left), CH₃OD (top right), HDO (bottom left), and CH₂DCN (bottom right) deuterium fractionations observed towards the hot core of a sample of low-mass, intermediate-mass, and high-mass protostars with sub-millimeter interferometers as a function of the dust temperature of the surrounding cloud measured with the Herschel or Planck telescopes (see values in Table 3). Green, red, and blue curves show the deuterations predicted by the GRAINOBLE astrochemical model in ices as a function of the dust temperature assumed in the dark cloud simulation at n_H = 10⁴, n_H = 10⁵ and 10⁶ cm⁻³, respectively, for at 0.1 × t_FF (dotted lines), t_FF (solid), and 10 × t_FF (dashed), where t_FF is the free-fall time for the corresponding density. No predictions are given for the CH₃ CN deuteration because this molecule is thought to be mostly produced in the vicinity of protostars either on ices or in the gas phase through warmer chemistry. LM, IM, and HM stand for low-mass, intermediate-mass, and high-mass protostars, respectively. See text for more details.