We present a study of transition state optimization with the divide-and-conquer (DC) density functional theory (DFT) method, using the addition of HF to trans-2-butene as an example. We preysent relative energies and geometries for each state in the reaction. We show that the DC method gives results that agree well with those obtained by conventional Kohn-Sham DFT methods, using the same exchange-correlation functional and basis set.