Calculated fractional abundances for 11 COMs detected toward Sgr B2(N2-N5). Panels a: N-bearing species C₂H₅CN, C₂H₃CN, CH₃CN, NH₂CHO, and CH₃NCO, as well as CH₃SH. Panels b: O-bearing species CH₃OH, C₂H₅OH, CH₃OCHO, CH₃OCH₃, and CH₃CHO. The results for the standard models, N(2-5)-T15-CR1, are shown from top to bottom, as a function of the temperature in the envelope of the sources during the free-fall collapse phase. In each panel the timescale shown at the top is derived from the time-dependent evolution of the temperature in the envelopes of the sources (see Sect. 3.5.2). In each panel, the solid lines show the fractional abundances (with respect to total hydrogen) in the gas phase while the dotted lines show the abundances of the same species on the grains (ice surface+mantle).