Theoretical studies of monoyttrium carbides, YCn, for n = 2-6, are presented. Consideration of several alternative structures leads to the kite, fan, and linear structures as the most attractive candidates for the ground states of different YCn complexes. The Y-C bond is strongly ionic due to the electron transfer from the yttrium to carbon atoms. The computed enthalpies of formation of YCn, atomization, and dissociation energies of these species are close to the corresponding experimental data. We compare the thermodynamic properties thus obtained from our theory with the experimentally estimated Gibbs energy functions and heat content functions using assumed structures.