C-RNTI (Cell RNTI) is an ID used to identify the RRC Connection and scheduling that is dedicated to a particular UE - used for the transmission to a specific UE after RACH.
While TC-RNTI (or Temporary C-RNTI) is a temporary ID inside MAC RAR (Random Access Response), which is generated by eNodeB as a response to the Random Access Preamble transmitted by the UE, as part of the Random Access procedure.