  The chemical and physical evolution of starless and pre-stellar cores are of
paramount importance to understanding the process of star formation. The Taurus
Molecular Cloud cores TMC 1-C and TMC 1-CP share similar initial conditions and
provide an excellent opportunity to understand the evolution of the pre-stellar
core phase. We investigated the evolutionary stage of starless cores based on
observations towards the prototypical dark cores TMC 1-C and TMC 1-CP, mapping
them in the CS $3\rightarrow 2$, C$^{34}$S $3\rightarrow 2$, $^{13}$CS
$2\rightarrow 1$, DCN $1\rightarrow 0$, DCN $2\rightarrow 1$, DNC $1\rightarrow
0$, DNC $2\rightarrow 1$, DN$^{13}$C $1\rightarrow 0$, DN$^{13}$C $2\rightarrow
1$, N$_2$H$^+$ $1\rightarrow 0$, and N$_2$D$^+$ $1\rightarrow 0$ transitions.
We performed a multi-transitional study of CS and its isotopologs, DCN, and DNC
lines to characterize the physical and chemical properties of these cores. We
studied their chemistry using the state-of-the-art gas-grain chemical code
Nautilus and pseudo time-dependent models to determine their evolutionary
stage. Observational diagnostics seem to indicate that TMC 1-C is in a later
evolutionary stage than TMC 1-CP, with a chemical age $\sim$1 Myr. TMC 1-C
shows signs of being an evolved core at the onset of star formation, while TMC
1-CP appears to be in an earlier evolutionary stage due to a more recent
formation or, alternatively, a collapse slowed down by a magnetic support.
