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 were 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 H₂CO and DCO⁺ line ratios. The temperature of the outflow cavity, traced by c-C₃H₂, on the other hand, shows a relation with bolometric luminosity and an anticorrelation 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.