The densest and coldest regions of molecular clouds, though seemingly inactive, often contain prestellar cores that exhibit emission of various chemical species indicative of star formation processes. The Orion B molecular cloud is a laboratory of different environments, from UV-illuminated to cold and shielded, which directly contributes to the diversity of sources forming there. In this talk, I will present the results of an analysis based on the observations of the ORION-B observational programme performed with the IRAM 30m telescope (Pety et al., 2017; Einig et al., 2023). A sample of pre-stellar cores and protostars was selected based on the Herschel catalogue (Konyves et al., 2020), and their molecular line emission was characterised for selected species, including four CO isotopologues, organic compounds such as H2CO and CH3OH, nitrogen-bearing species like N2H+ and HNC, and deuterated species including DCO+ and DNC. The abundances measured in the local thermodynamic equilibrium (LTE) scenario will be presented, as well as those measured for a selected number of cores using a non-LTE multilayer model (Segal et al., 2024). General trends indicate a strong diversity of sources and chemical species, as evidenced by CO depletion and environmental dependence as traced by dust temperatures. These results along with their interpretations will be presented during the talk.