Evolution of key elements of the inner 6 M_⊙ core structure as a function of time from carbon ignition to core collapse for models with the same core mass and a different central carbon abundances X_C. (a) Kippenhahn diagram with selected elements. Full and dashed lines indicate the carbon and neon-burning fronts, respectively. Shaded (hatched) regions show convective carbon (neon) burning regions in the core. The iron-core masses are indicated with dash-dotted lines. The gray horizontal dashed line indicates the classical Chandrasekhar limit. The inset figure shows the final compactness of these models as a function of decreasing X_C. (b) Total mass of ¹²C in the convective carbon-burning shells for each of the models as a function of time.