  Context: Simulations suggest that gas heating due to radiative feedback is a
key factor in whether or not multiple protostellar systems will form. Chemistry
is a good tracer of the physical structure of a protostellar system, since it
depends on the temperature structure.
  Aims: We aim to study the relationship between envelope gas temperature and
protostellar multiplicity.
  Methods: Single dish observations of various molecules that trace the cold,
warm and UV-irradiated gas are used to probe the temperature structure of
multiple and single protostellar systems on 7000 AU scales.
  Results: Single, close binary, and wide multiples present similar current
envelope gas temperatures, as estimated from H$_2$CO and DCO$^+$ line ratios.
The temperature of the outflow cavity, traced by c-C$_3$H$_2$, on the other
hand, shows a relation with bolometric luminosity and an anti-correlation with
envelope mass. Although the envelope gas temperatures are similar for all
objects surveyed, wide multiples tend to exhibit a more massive reservoir of
cold gas compared to close binary and single protostars.
  Conclusions: Although the sample of protostellar systems is small, the
results suggest that gas temperature may not have a strong impact on
fragmentation. We propose that mass, and density, may instead be key factors in
fragmentation.
