C-. People get in with Cs in the prereqs all the time, including ochem. If there are As in gen chem, Bs in physics and a good overall science GPA it isn't going to be that big of a deal. Things like a solid upward trend and As in upper division classes will help sweeten the deal. Everyone knows ochem is difficult. Half the doctors I talk to when it comes up that I'm finishing up the organic series will say, "Yup...ochem...my only Cs in college."