Electroexcitation of the dominantly T≡1 particle-hole states of 12C are studied in the framework of the harmonic oscillator shell model. Configurations mixing is allowed and the Hamiltonian is diagnoalized in the presence of the modified surface-delta interaction (MSDI). All possible T≡1 single-particle-hole states of all allowed angular momenta are considered in a basis including single-particle states up to the 1f-2p shell. Resulting mixed states lying close in energy are grouped together into complexes. A comparison with the experiment shows that this model is able to predict the location of states in a good way