  The extremely young Class 0 object B1b-S and the first hydrostatic core
(FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical
changes produced in the elusive transition from the prestellar core to the
protostellar phase. We present 40"x70" images of Barnard 1b in the 13CO 1->0,
C18O 1->0, NH2D 1_{1,1}a->1_{0,1}s, and SO 3_2->2_1 lines obtained with the
NOEMA interferometer. The observed chemical segregation allows us to unveil the
physical structure of this young protostellar system down to scales of ~500au.
The two protostellar objects are embedded in an elongated condensation, with a
velocity gradient of ~0.2-0.4 m s^{-1} au^{-1} in the east-west direction,
reminiscent of an axial collapse. The NH2D data reveal cold and dense
pseudo-disks (R~500-1000 au) around each protostar. Moreover, we observe
evidence of pseudo-disk rotation around B1b-S. We do not see any signature of
the bipolar outflows associated with B1b-N and B1b-S, which were previously
detected in H2CO and CH3OH, in any of the imaged species. The non-detection of
SO constrains the SO/CH3OH abundance ratio in the high-velocity gas.
